A comparison of nitrogen dioxide (NO2) in nitrogen
standards at 10 μmol/mol by Fourier Transform Infrared
Spectroscopy (FT-IR)
(Final report of the pilot study CCQM-P110-B1)
Edgar Flores*1, Faraz Idrees1, Philippe Moussay1, Joële Viallon1, Robert Wielgosz1, Teresa Fernández2,
Andrés Rojo2, Sergio Ramírez2, Nobuyuki Aoki3, Kenji Kato.3, Lee Jeongsoon4, Dongmin Moon4 and
Jin-Seog Kim4, A. Harling5, M. Milton5, Damian Smeulders6, Franklin R. Guenther7, Lyn Gameson7,
Angelique Botha8, James Tshilongo8, Napo Godwill Ntsasa8, Miroslava Valková9, Leonid A.
Konopelko10, Yury A. Kustikov10, Vladimir S. Ballandovich10, Elena V. Gromova10, Dirk Tuma11, Anka
Kohl11 and Gert Schulz11.
1
Bureau International des Poids et Mesures (BIPM), Pavillon de Breteuil, F-92312 Sevres Cedex.
Centro Español de metrología (CEM), Calle Alfar, 2, 28760 Tres, Cantos (Madrid), Spain.
National Metrology Institute of Japan (NMIJ), 305-8563 1-1-1 Umesono, Tsukuba Ibaraki, Japan.
4
Korea Research Institute of Standards and Science (KRISS),1, Doryong-Dong, Yuseong-Gu, Daejeon 305-340, Korea
5
National Physical Laboratory (NPL), Hampton Road, Teddington, Middx, TW11 0LW, UK.
6
National Measurement Institute Australia (NMIA), Bradfield Road, P.O. Box 264, NSW 2070 Lindfield
7
National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, MD 20899-8393, USA
8
National Metrology Institute of South Africa (NMISA), CSIR, Building 4 West, Meiring Naude Road Brummeria, 0184,
Pretoria, South Africa.
9
Slovak Institute of Metrology (SMU), Karloveská 63, SK-842 55 Bratislava, Slovak Republic.
10
D.I.Mendeleyev Institute for Metrology (VNIIM), 19 Moskovsky pr., St. Petersburg, 190005 Russia.
11
Federal Institute for Materials Research and Testing (BAM), Unter den Eichen 87, 12205 Berlin, Germany.
2
3
Coordinating laboratories:
Bureau International des Poids et Mesures (BIPM)
VSL Dutch Metrology Institute
Study coordinator: Edgar Flores (BIPM)
Correspondence to be addressed to: Edgar Flores [email protected]
(Tel: + 33 1 45 07 70 92)
Field: Amount of substance
Organizing Body: CCQM
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 1 of 76
Index
1.
RATIONAL FOR COMPARISON
4
2. QUANTITIES AND UNITS
4
3.
4
SCHEDULE
4. MEASUREMENT STANDARDS
4
Preparation and value assignment
4
Purity analysis
5
Stability of the mixtures
6
Deviations from the protocol
6
5.
REFERENCE VALUES FOR CYLINDERS
17
6.
MEASUREMENT PROTOCOL
17
7.
MEASUREMENT METHODS
18
8
RESULTS
18
9.
DISCUSSION
24
10. CONCLUSION
26
ANNEX 1- BIPM VALUE ASSIGNMENT PROCEDURE
27
1.
Description of the facility
27
2.
Measurement protocol of the BIPM
30
3.
BIPM measurement uncertainties and analyser response
31
4.
Covariance between two dynamically generated gas mixtures
34
5.
FT-IR analysis of gas standards
35
6.
FT-IR Spectra acquisition procedure
35
7.
Quantitative analysis of nitric acid
36
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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8.
Uncertainty budget
36
9.
Regression analysis
37
10.
Determination and validation of analysis functions
37
ANNEX 2 - MEASUREMENT REPORTS OF PARTICIPANTS
38
Centro Español de metrología (CEM)
38
Korea Research Institute of Standards and Science (KRISS)
41
National Measurement Institute Australia (NMIA)
44
National Metrology institute of Japan (NIMJ)
46
National Institute of Standards and Technology (NIST)
49
National Physical Laboratory (NPL)
52
National Metrology Institute of South Africa (NMISA)
57
Slovak Institute of Metrology (SMU)
60
Mendeleyev Institute for Metrology (VNIIM)
68
Federal Institute for Materials Research and Testing (BAM)
71
Bureau International des Poids et Mesures (BIPM)
74
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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1. Rational for comparison
This pilot study compares the performance of participants in analysing an unknown
mixture of nitrogen dioxide in nitrogen (at a nominal mole fraction of 10 µmol/mol.) by
comparison with their own standards using FT-IR spectroscopy. It uses the same
standard gas mixtures as were used in the key comparison CCQM-K74 (1).
The level of comparability between laboratories in this Pilot Study was evaluated and
compared to that in CCQM-K74. In CCQM-K74, most participants used
chemiluminescence, with a small number using UV absorption or FT-IR spectroscopy.
These last two techniques are of particular interest because they do not exhibit any cross
sensitivity to nitric acid (HNO3), which was known to be present in the mixtures used
for the comparison.
2. Quantities and Units
In this protocol the measurand was the mole fraction of nitrogen dioxide in nitrogen*,
with measurement results being expressed in mol/mol and its multiples μmol/mol or
nmol/mol.
(*the nitrogen balance gas contains nominally 1000 µmol/mol of oxygen)
3. Schedule
The revised schedule of the project was as follows:
June 2009
June 2009- August 2009
September 2009
October 2009- January 2010
February 2010
March 2010 – May 2010
February 2010 – May 2010
July 2010
September 2011
Shipment of cylinders to the BIPM
Analysis of mixtures at the BIPM
Shipment of cylinders from the BIPM to participants
Analysis of mixtures by the participants
Shipment of cylinders back from participants to the BIPM
2nd set of analysis of mixtures at the BIPM
Reports of the participants
Distribution of Draft A of this report
Distribution of Draft B V0.1 of this report
4. Measurement standards
Preparation and value assignment
The gas mixtures were prepared by the Dutch Metrology Institute (VSL). The nitrogen
dioxide gas mixtures were contained in passivated aluminium cylinders of 5 L. The
cylinders were pressurized to about 12 MPa.
The nitrogen dioxide gas standards were produced by gravimetric preparation in
accordance with the International Standard ISO 6142:20011.
1
ISO 6142:2001: Gas analysis-Preparation of calibration gas mixtures-Gravimetric method.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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Each cylinder was value assigned by the BIPM, with its dynamic gas facility described
in ANNEX 1, before and after the participant’s measurements. The VSL and BIPM
values and measurements are given in Table 1 and Table 2 where:
xVSL
is the value assigned by VSL based on gravimetric preparation;
uprep(xVSL)
the standard uncertainty of the VSL values with contributions due to
gravimetry and purity analysis;
uver(xVSL)
the standard uncertainty including contributions from verification
associated with the assigned value xVSL;
xBIPM1
the first BIPM measurement result (prior to sending out cylinders to
participants);
u(xBIPM1)
the standard uncertainty of the first BIPM measurement result,
including losses and drift terms as explained in section 5;
xBIPM2
the second BIPM measurement result (on return of cylinders from
participants);
u(xBIPM2)
the standard uncertainty of the second BIPM measurement result;
Purity analysis
From previous studies carried out by the BIPM and VSL it was expected that the
mixtures would contain quantifiable amounts of HNO3. The analysis of the gas mixtures
at the BIPM with FT-IR spectroscopy confirmed the presence of and permitted the
quantification of nitric acid in the gas mixtures. Table 3 list the nitric acid mole
fractions found in the gas standards. To verify the stability of the gas mixtures the purity
analysis was repeated when the gas mixtures were returned to the BIPM provided that
the participants returned the cylinders with the minimum gas pressure required as
described in the comparison protocol (see Table 4).
Table 3 lists:
Cylinder
the identification code of the cylinder received by the participating
laboratory;
xHNO3(1)
the mole fraction of nitric acid measured in the standard by the BIPM
(prior to sending standards to participants);
u(xHNO3(1))
the standard uncertainty associated with the nitric acid mole fraction
measurement;
xHNO3(2)
the mole fraction of nitric acid measured in the standard by the BIPM
(following return of standards to the BIPM);
u(xHNO3(2))
the standard uncertainty associated with the nitric acid determination by
FT-IR spectroscopy after the participants measurements.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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Stability of the mixtures
The nitrogen dioxide mole fractions measured by the BIPM before and after
measurements by participants are shown in Figure 1. The error bars in the first series of
measurements represent the standard uncertainty associated with the BIPM
measurement results including contributions from the dynamic preparation of nitrogen
dioxide gas mixtures, NO2 losses in the permeation system of the BIPM and an
observed drift in the nitrogen dioxide mole fractions measured by the BIPM before and
after the participant’s measurements. For further information see the ANNEX 2 of the
report International comparison CCQM-K74: Nitrogen dioxide, 10 μmol/mol. The error
bars in the second series of measurements represent the standard uncertainty associated
with the BIPM measurement results including the contributions from the dynamic
preparation of nitrogen dioxide gas mixtures. The difference between the BIPM series
of measurements for each standard is plotted in Figure 2.The NO2 mole fraction in all
cylinders was found to be in the range from 10.143 μmol/mol to 10.435 μmol/mol as
measured by the BIPM.
The amount of nitric acid found in each cylinder was consistent with the difference
between the gravimetric preparation value and BIPM’s analytical value for the nitrogen
dioxide amount fraction, and accounts for the conversion of nitrogen dioxide to nitric
acid (reacting with residual water and oxygen in the gas standards) and limited by the
amount of water present. Figure 3 plots the nitric acid mole fractions measured in each
gas standard before and after measurements by the participants. Changes in the mole
fractions of nitrogen dioxide and nitric acid in each cylinder during the period of the
comparison were well within the measurement uncertainties of these values. The
uncertainty budget for the BIPM measurement result contains a component which
covers any change in value due to instability of the gas transfer standard. The difference
between the series on nitric acid mole fractions measured by the BIPM was plotted in
Figure 4. The mixtures stability can be confirmed in the summation of nitrogen dioxide
and nitric acid mole fractions of the first and second series of measurements shown in
Figure 5.
Deviations from the protocol
The BIPM was unable to perform a second measurement of nitric acid content in gas
mixtures 930659 and 930649, as the participating laboratories that had made
measurements on these cylinders had not followed the comparison protocol and
returned the cylinders with insufficient gas to make these measurements.
Cylinder 930722 was not returned on time to the BIPM and no additional measurements
could be made on this cylinder.
Cylinder 930697 was analyzed by the BIPM to provide a BIPM result in this
comparison. This cylinder was sent after to NIST2. Unlike other participants, the NIST
performed its analysis on two different cylinders: cylinder 930654 during CCQM-K74
and cylinder 930697 during CCQM-P110. This should not impact the results as all
reference values are given by the BIPM.
2
The cylinder 930697, originally assigned to the BIPM, was sent to NIST before the second series of
measurements due that the internal pressure of NIST cylinder, 930654, was extremely low to take part in
the present comparison after its participation in the Key comparison CCQM-K74.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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VSL preparation values
Certificate
Preparation
Number
number
date
of Cylinder
3221115-02
3221115-22
3221115-23
3221115-21
3221115-08
3221115-15
3221115-11
3221115-25
3221115-18
3221115-20
3221115-11
24/02/2009
09/04/2009
09/04/2009
08/04/2009
03/04/2009
02/04/2009
01/04/2009
10/04/2009
03/04/2009
08/04/2009
01/04/2009
#930659-PRM
#930655-PRM
#930662-PRM
#930649-PRM
#930670-PRM
#930661-PRM
#930697-PRM
#930676-PRM
#930713-PRM
#930722-PRM
#930697-PRM
Gravimetric
standard
Certified standard
uncertainty
uncertainty
xVSL
(μmol/mol)
uprep(xVSL)
(μmol/mol)
uver(xVSL)
(μmol/mol)
10.604
10.608
10.606
10.609
10.610
10.603
10.604
10.600
10.597
10.620
10.600
0.003
0.003
0.003
0.003
0.003
0.003
0.002
0.003
0.003
0.003
0.003
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
Assigned
NO2 mole
fraction
Table 1. Characteristics of gravimetric mixtures as provided by VSL.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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BIPM measurement results
1st BIPM
Number
Standard
Measurement
of Cylinder
date
1st
measurement
Measurement
NO2 mole fraction
measurement
xBIPM1
uncertainty
μmol/mol
μmol/mol
date
u(xBIPM1)
2nd measurement
2nd BIPM
assigned
NO2 mole
fraction
uncertainty
xBIPM2
μmol/mol
u(xBIPM2)
μmol/mol
Standard
Δx=
(xBIPM2xBIPM1)
μmol/mol
u(Δx)
μmol/mol
2u(Δx)
μmol/mol
#930659-PRM
19/08/2009
10.226
0.042
*
#930655-PRM
18/08/2009
10.347
0.042
01/04/2010
10.352
0.035
0.005
0.054
0.110
#930662-PRM
18/08/2009
10.378
0.042
30/03/2010
10.353
0.035
-0.025
0.054
0.110
#930649-PRM
18/08/2009
10.347
0.042
*
#930670-PRM
31/08/2009
10.146
0.042
07/04/2010
10.093
0.035
-0.053
0.054
0.110
#930661-PRM
19/08/2009
10.270
0.042
31/03/2010
10.265
0.035
-0.005
0.054
0.110
#930697-PRM
25/08/2009
10.343
0.042
31/03/2010
10.343
0.035
0.000
0.054
0.110
#930676-PRM
28/08/2009
10.435
0.042
31/03/2010
10.421
0.035
-0.014
0.054
0.110
#930713-PRM
29/08/2009
10.320
0.042
01/04/2010
10.284
0.035
-0.037
0.054
0.110
#930722-PRM
28/08/2009
10.350
0.042
**
#930697-PRM
25/08/2009
10.343
0.042
31/03/2010
10.343
0.024
0.000
0.048
0.096
Table 2. Results of BIPM NO2 mole fraction measurements. * Insufficient gas for second measurement. *** Standard not yet returned to the BIPM.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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BIPM HNO3 Measurements
Measurement
Cylinder
xHNO3(1)
u(xHNO3(1))
(μmol/mol)
(μmol/mol)
date
Measurement
12/08/2009
0.348
0.027
*
#930655-PRM
30/07/2009
0.114
0.021
20/04/2010
0.155
0.022
*
28/07/2009
u(xHNO3(2))
Δx=
(xHNO3(2)xHNO3(1))
μmol/mol
(μmol/mol)
(μmol/mol)
u(Δx)
μmol/mol
2u(Δx)
μmol/mol
0.133
0.021
0.019
0.030
0.059
0.140
0.021
-0.015
0.030
0.061
date
#930659-PRM
#930662-PRM
xHNO3(2)
01/05/2010
#930649-PRM
11/08/2009
0.237
0.024
#930670-PRM
12/08/2009
0.473
0.032
03/05/2010
0.531
0.034
0.058
0.047
0.093
#930661-PRM
30/07/2009
0.199
0.023
21/04/2010
0.240
0.024
0.041
0.033
0.065
#930697-PRM
28/07/2009
0.141
0.021
30/04/2010
0.172
0.022
0.031
0.031
0.061
0.081
0.020
0.099
0.021
0.018
0.029
0.058
0.197
0.022
0.184
0.022
-0.013
0.032
0.063
***
30/04/2010
0.172
0.022
0.031
0.031
0.061
#930676-PRM
#930713-PRM
11/08/2009
12/08/2009
#930722-PRM
31/07/2009
0.145
0.021
#930697-PRM
28/07/2009
0.141
0.021
01/05/2010
21/04/2010
Table 3. Nitric acid mole fraction measured in cylinder gas standards by the BIPM using FT-IR spectroscopy. * Insufficient gas for second measurement. *** Standard not
yet returned to the BIPM.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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Lab
Certification
date
Number
of Cylinder
Date of
return
NPL
SMU
NMIA
NMISA
NMIJ
KRISS
NIST
CEM
VNIIM
BAM
BIPM
24/02/2009
09/04/2009
09/04/2009
08/04/2009
19/03/2009
02/04/2009
20/03/2009
10/04/2009
03/04/2009
08/04/2009
20/03/2009
#930659-PRM
#930655-PRM
#930662-PRM
#930649-PRM
#930670-PRM
#930661-PRM
#930697-PRM
#930676-PRM
#930713-PRM
#930722-PRM
#930697-PRM
26-Jan-2010
02-Feb-2010
26-Feb-2010
24-Feb-2010
19-Feb-2010
26-Feb-2010
15-Mar-2010
02-Mar-2010
16-Feb-2010
***
In place
pressure on
departure
Mpa
9.0
10.0
9.5
10.5
10.0
9.5
8.5
10.0
10.0
9.8
-
pressure on
return
Mpa
4.0*
7.5
7.0
2.5*
7.0
5.5
6.0
6.2
7.2
-
Table 4. Departure and return pressure of the gas standards after being measured by the participating laboratories.
* Insufficient gas for 2nd series of BIPM measurements (≤5MPa). *** Standard not yet returned to the BIPM.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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1st BIPM
NO2 mole
fraction
measurement
xBIPM1
Standard
uncertainty
u(xBIPM1)
2nd BIPM
NO2 mole
fraction
measurement
xBIPM2
Standard
uncertainty
u(xBIPM2)
xBIPM1
+
μmol/mol
μmol/mol
μmol/mol
μmol/mol
xHNO3(1)
u(xBIPM1+
xHNO3(1))
10.226
10.347
10.378
10.347
10.146
10.270
10.343
10.435
10.320
10.350
10.343
0.042
0.042
0.042
0.042
0.042
0.042
0.041
0.042
0.042
0.042
0.041
*
10.351
10.353
*
10.093
10.265
10.343
10.421
10.284
**
10.343
10.574
10.461
10.533
10.584
10.619
10.469
10.484
10.516
10.517
10.495
10.484
0.050
0.046
0.047
0.048
0.052
0.047
0.046
0.047
0.048
0.047
0.046
0.035
0.035
0.035
0.035
0.035
0.035
0.035
0.024
2u
2u
(xBIPM1+
xBIPM2
+
u(xBIPM2+
(xBIPM2+
xHNO3(1))
xHNO3(2)
xHNO3(2))
xHNO3(2))
10.484
10.493
0.041
0.041
0.082
0.082
10.624
10.505
10.515
10.520
10.468
0.049
0.042
0.041
0.041
0.041
0.098
0.084
0.083
0.081
0.083
10.515
0.033
0.066
0.099
0.093
0.094
0.095
0.105
0.095
0.092
0.093
0.096
0.093
0.092
Table 5. Summation of Nitrogen Dioxide and Nitric Acid Mole fractions for each standard based on BIPM measurements.
* Insufficient gas for second measurement. *** Standard not yet returned to the BIPM.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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11.00
10.90
10.80
BIPM Nitrogen dioxide
mole fraction / μmol/mol
10.70
10.60
1st
2nd
10.50
10.40
10.30
10.20
10.10
10.00
930659
930655
930662
930649
930670
930661
930697
930676
930713
930722
Figure 1. First and second series of nitrogen dioxide mole fraction measurements by the BIPM prior to sending standards to participating laboratories. The second series of
measurements was done after the return of standards from participating laboratories The error bars of the first series of measurements represent the standard uncertainty (k =
1) associated with the BIPM measurement results including contributions from the dynamic preparation of nitrogen dioxide gas mixtures, NO2 losses in the permeation system
of the BIPM and an observed drift in the nitrogen dioxide mole fractions measured by the BIPM before and after the participant’s measurements. For further information see
the ANNEX 2 of the report International comparison CCQM-K74: Nitrogen dioxide, 10 μmol/mol. The error bars in the second series of measurements represent the standard
uncertainty (k = 1) associated with the BIPM measurement results including the contributions from the dynamic preparation of nitrogen dioxide gas mixtures.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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0.50
0.40
0.30
Δx (xBIPM1-xBIPM2) / μmol/mol
0.20
0.10
0.00
-0.10
-0.20
-0.30
-0.40
-0.50
930659
930655
930662
930649
930670
930661
930697
930676
930713
930722
930697
Figure 2. Difference between the BIPM series of measurements of nitrogen dioxide for each standard. The error bar represents the expanded uncertainty at a 95% level of
confidence.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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1.00
0.90
0.80
BIPM Nitric acid
mole fraction / μmol/mol
0.70
0.60
1st
2nd
NMI's
0.50
0.40
0.30
0.20
0.10
0.00
930659
930655
930662
930649
930670
930661
930697
930676
930713
930722
930697
Figure 3. First (red) and second (blue) series of nitric acid mole fraction measurements by the BIPM and nitric acid mole fractions found by the participating laboratories
(green). The error bar represents the standard uncertainty (k=1).
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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0.500
0.400
0.300
Δx (x HNO3(1)-x HNO3(2))
mole fraction / μmol/mol
0.200
0.100
0.000
-0.100
-0.200
-0.300
-0.400
-0.500
930659
930655
930662
930649
930670
930661
930697
930676
930713
930722
930697
Figure 4. Difference between the second and first series of nitric acid mole fraction measurements by the BIPM. The error bar represents the expanded uncertainty at a 95%
level of confidence.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 15 of 76
11.00
10.90
10.80
BIPM Nitrogen dioxide + Nitric acid
mole fraction / μmol/mol
10.70
10.60
10.50
10.40
10.30
10.20
10.10
10.00
930659
930655
930662
930649
930670
930661
930654
930676
930713
930722
930697
Figure 5. Summation of Nitrogen Dioxide and Nitric Acid Mole fractions in each standard based on BIPM measurements. Red: First measurements. Black: Second
measurements. The error bar represents the expanded uncertainty at a 95% level of confidence.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 16 of 76
5. Reference Values for Cylinders
During the 24th and 25th meetings of the CCQM GAWG it was agreed that the reference
value for this comparison was to be based on BIPM measurement results prior to
distribution of gas standards to participants. The BIPM’s measurements clearly indicate
the presence of nitric acid in the gas mixtures ranging from 100 nmol/mol to 350
nmol/mol. The nitrogen dioxide gravimetric preparation values provided by VSL were
not used as the reference values for the comparison as they do not account for the
presence of nitric acid in the standards, arising from the conversion of NO2 to nitric acid
through the reaction with oxygen and residual water in the cylinders. The current
hypothesis is that the water must have been present on the cylinder coatings. In the
current version of the report, laboratory results are compared to BIPM values, since they
correctly account for the presence of nitric acid in the gas mixtures. Furthermore, the
agreement between the summation of nitric acid and nitrogen dioxide mole fractions
with the initial amount of nitrogen dioxide (prior to any reaction) expected from static
gravimetric preparation values further confirms the hypothesis of the loss mechanism of
NO2 in the cylinders.
For each cylinder, the reference value is the NO2 mole fraction assigned by the BIPM
(first measurement). Following the CCQM GAWG guidance, it was decided that the
standard uncertainty of the reference value (xref) was to be calculated from the following
equation


u ref x NO2  (u ( x BIPM )) 2  (u ( x NO 2 Losses )) 2  (u ( x Drift )) 2
(1)
where u ( xBIPM ) is the uncertainty associated with the value assigned by the BIPM,
u ( xNO 2 Losses ) the uncertainty contribution due to NO2 losses equivalent to 5.7 nmol/mol
and u ( xDrift ) the uncertainty contribution due to observed drift in NO2 estimated to be
21 nmol/mol. This leads to an overall standard uncertainty of the reference value of
0.041 μmol/mol. A full discussion of the uncertainty of the reference value is included
in the report International comparison CCQM-K74: Nitrogen dioxide, 10μmol/mol.
The permeation of nitric acid from NO2 permeation tubes was detected and quantified
by the BIPM, and the BIPM’s values are corrected to avoid systematic errors caused by
this issue. This is fully described in ANNEX 1- BIPM Value assignment procedure.
6. Measurement protocol
The measurement protocol requested participants to use FT-IR spectroscopy methods
calibrated and traceable to gas standards. Likewise, it was requested that participants
provide the value and uncertainty of the nitrogen dioxide mole fraction measured by the
laboratory, a complete uncertainty budget and a description of their gas analysis
procedure.
The participant’s reports are included in ANNEX 2 - Measurement reports of
participants.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 17 of 76
7. Measurement methods
As mentioned above, the protocol for this pilot study required participants to use FT-IR
spectroscopy. Table 6 summarizes the main characteristics of the instrumentation and
calibration methods need by each laboratory. From Table 6 we can conclude that:
-
five of the ten participating laboratories used Nicolet spectrometers and
Omnic acquisition software;
of the participating laboratories nine used gas mixtures contained in high
pressure cylinders as calibration references and just the BIPM used mixtures
from its permeation facility;
of the ten laboratories using gas mixtures as standards nine were traceable to
their own gravimetric standards
nearly all participants measured their gas mixtures near ambient conditions
(297 K and ~100 kPa);
more than half of the participants performed water corrections;
half of the participants used a spectral region within the range (1500-1800)
cm-1 and half used the spectral region within the range (2800-300) cm-1 or
both;
the resolution range used by the participants was (0.25 to 4) cm-1; and
eight of the ten participating laboratories used an optical path length between
the range of (4.8-10) m, one 0.1m and one 20 m; and
two of the ten participating laboratories confirmed the presence of nitric acid
in their gas mixture.
8 Results
The results submitted by the participants are plotted in Figure 6. The evaluation of the
level of consistency between the participating laboratories was done by comparison
between the reported nitrogen dioxide mole fractions by participating laboratories and
the BIPM FT-IR measurements (1st series) for each cylinder.
The consistency between the participating laboratory’s results and the BIPM reference
values is presented in terms of a difference (D) defined as:
D  x NMI  x ref
(2 )
where x NMI denotes the amount of substance fraction as measured by the participating
national metrology institute (NMI) and xref the reference value given by the BIPM.
The standard uncertainty in D is:
2
2
u ( D)  u NMI
 u ref
(3 )
and the expanded uncertainty at 95% confidence level
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 18 of 76
U ( D)  k  u ( D)
(4 )
where k denotes the coverage factor, taken as k = 2 (normal distribution, approximately
95% level of confidence).
The differences between BIPM and NMI’s assigned values for each of the circulated
gas standards are listed in Table 7 where:
Laboratory
is the acronym of the participating national metrology institute;
Cylinder
the identification code of the cylinder received by the participating
laboratory;
xref
the reference value (1st series of BIPM measurement results);
u(xref)
the uncertainty of the reference value;;
xLab
the result as reported by the participating laboratory;
u(xLab)
the standard uncertainty of the reported value xLab as reported by the
participating laboratory ;
D
the difference in amount of substance fraction as measured by the
laboratory and x BIPM the BIPM value; and
u(D)
the standard uncertainty of the difference of amount of substance;
The difference (D) in nitrogen dioxide reported values by participating laboratories and
the BIPM are plotted in Figure 7. In this figure, the result attributed to the BIPM is
based on the second analysis of a particular cylinder (#930697-PRM), using the first
measurement made on this gas mixture as reference value.The method used by the
BIPM to calculated its uncertainty value, u(xLab), is carefully described elsewhere(1).
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 19 of 76
Laboratory
NPL
SMU
NMIA
NMISA
NMIJ
KRISS
NIST
CEM
VNIIM
BAM
BIPM
Varian
Excalibur
Nicolet
6100
Nicolet
Magna IR 560
JASCO
Bruker
Nicolet
6700
PerkinElmer
FT-IR Spectrometer
Nicolet
6700
Monitoring
Ldt, Russia
Nicolet
Nexus
Nicolet
Nexus
8.00
10.00
10.00
10.00
0.10
9.61
10.00
20.00
4.80
10
6.40
Bracketing
(8-12) μmol/mol
4 mixtures
at 10 μmol/mol
1 mixture
2 mixtures
at 10 μmol/mol,
CLS
2 mixtures
(9.43, 12.2)
μmol/mol
GLS, linear,
Bracketing,
Permeation-dynamic
mixtures
Traceability
own
gravimetric
standards
own
gravimetric
standards
own
gravimetric
standards
own
gravimetric
standards
1 mixture
Normalized
response of nine
NO2 peaks
(See pag. 49)
own
gravimetric
standards
3 mixtures,
GLS, linear,
(5, 10, 15)
μmol/mol
own
gravimetric
standards
5 mixtures
(0.99, 2.52,
7.23, 10.48 and
49.72)
μmol/mol
own
gravimetric
standards
4 mixtures
Calibration method
2 mixtures
peak area
integration
NPL
gravimetric
standards
own
gravimetric
standards
own
gravimetric
standards
own
permeation tube
system
298
294.7
333.15
295.45
-
-
296.45
293
299.2
302.6
302.6
105.59
99.6
86.65
109.5
-
-
101.16
102.2
102.7
106
106
Omnic
Omnic
OPUS
Omnic
Fspec
Omnic
Omnic-IMACC
Omnic
Omnic
FCM
Omnic
Fspec
Omnic
IMACC
Excel
MALT
FCM
Excel
ASpec
Omnic
B_Least (ISO 6143)
Yes
Peak selection
Yes
Using the spectral
region
2840-2940 cm-1
Yes
Omnic software
procedure
None
None
Yes,
peaks selection
None
Yes
Vapor absorption
elimination
None
Yes
MALT interference
correction by GLS
and N2 purge in
FT-IR enclosure box
Gas cell (m)
Average gas cell
temperature (K)
Average gas cell presure
(kPa)
Spectrometer software
to:
control
Omnic
acquire
Omnic
analyze
Omnic
Did the participant
performed any water
correction?
if yes, how?
None
Varian
Resolutions
Varian
Resolutions
Varian
Resolutions
Spectra
Manager
Spectra
Manager
Spectra
Manager
Spectrum
software
Spectrum
software
IFSS (Imacc
Software)
Spectral range used for
the mole fraction
determination(cm-1)
Measurement resolution
(cm-1)
1600
(28602940)
1351-1887
2847-2941
1530-1670
2840-2940
1561-1656
-
-
2840-2940
-
1560-1650
2800-2950
1550-1650
0.5
0.25
0.25/0.5
0.5
4
1
0.125
2
1
1
1
u(xLab) /%
0.7
0.9
2.9
1.0
0.5
1.5
1.0
4.2
0.8
3.6
0.2
Table 6. Main FT-IR characteristics of the instrumentation and calibration methods submitted by the laboratories.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 20 of 76
CCQM-P110 B1
11.4
11.2
Laboratory measurement results
mole fractions / μmol/mol
11.0
10.8
10.6
10.4
10.2
10.0
9.8
9.6
NPL
SMU
NMIA
NMISA
NIMJ
KRISS
NIST
Laboratory
CEM
VNIIM
BAM
BIPM
Figure 6. Nitrogen dioxide amount of fraction as reported by the participating laboratories for CCQM-P110 B1. The error bar represents the standard uncertainty (k=1).
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 21 of 76
BIPM
Laboratory
NPL
SMU
NMIA
NMISA
NMIJ
KRISS
NIST
CEM
VNIIM
BAM
BIPM
Participants
Cylinder
xref
u(xref)
xLab
#930659-PRM
#930655-PRM
#930662-PRM
#930649-PRM
#930670-PRM
#930661-PRM
#930697-PRM
#930676-PRM
#930713-PRM
#930722-PRM
#930697-PRM
10.226
10.347
10.378
10.347
10.146
10.270
10.343
10.435
10.320
10.350
10.343
0.042
0.042
0.042
0.042
0.042
0.042
0.042
0.042
0.042
0.042
0.042
10.320
10.207
10.740
10.620
10.440
10.470
10.300
10.620
10.530
10.530
10.343
u(xLab)
0.070
0.095
0.315
0.110
0.055
0.160
0.100
0.445
0.085
0.375
0.024
D( xLab- xref)
0.094
-0.140
0.362
0.273
0.294
0.200
-0.043
0.185
0.210
0.180
0.000
u(D)
0.081
0.103
0.318
0.118
0.069
0.165
0.108
0.447
0.095
0.377
0.048
Table 7. Laboratory results for nitrogen dioxide measurements (μmol/mol).
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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u(D)
(k=2)
0.163
0.206
0.635
0.235
0.138
0.331
0.217
0.894
0.190
0.755
0.096
1.500
1.350
1.200
1.050
0.900
0.750
0.600
0.450
D (μmol/mol)
0.300
0.150
0.000
-0.150
-0.300
-0.450
-0.600
-0.750
-0.900
-1.050
-1.200
-1.350
-1.500
NPL
SMU
NMIA
NMISA
NIMJ
KRISS
Laboratory
NIST
CEM
VNIIM
BAM
BIPM
Figure 7. Difference between participants’ results and the reference value determined in CCQM-K74. The error bar represents the expanded uncertainty at a
95% level of confidence.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 23 of 76
9. Discussion
According to Figure 7 the majority of participants agree with the reference value. In
order to draw more conclusions on the specificity of the FT-IR technique, the same
results are plotted in Figure 8 together with CCQM-K74 results for those participants
that took part in both comparisons, excluding the CCQM-K74 results obtained by FTIR. In this figure, the similarity of the results confirms the good agreement between FTIR and the two other techniques which are UV photometry and chemiluminescence. A
different conclusion could have been expected, given that FT-IR analysers do not suffer
from a cross sensitivity to nitric acid (unlike chemiluminescence analysers), which was
observed in the circulated cylinders. As already concluded in CCQM-K74, the possible
presence of nitric acid at the same level in the primary standards used to calibrate the
FT-IR can explain this result, if the impurity was not detected in the FT-IR spectra and
accounted for in the results.
There is no evidence of any clear differences in the results due to the specific choices of
FT-IR set-up parameters made by the participants.
From Figure 8 it also appears that almost all participants attributed a larger uncertainty
to the FT-IR measurement results than to the two other techniques. Based on all
participant results in table 7, relative standard uncertainties ranging from 0.23% to 4.2%
were attributed to FT-IR based measurements of NO2 mole fractions. The majority
(seven participants) however attributed a relative standard measurement uncertainty of
less than 1.5 % to their measurement results, notably for participants that agreed with
the reference values in both this and CCQM-K74. This is finally similar to the relative
standard measurement uncertainties attributed to chemiluminescence and UV
absorption techniques, which ranged from 0.4% to 1.7% for the quantification of NO2
mole fractions at nominal 10 µmol/mol.
Since the FT-IR measurement technique is potentially capable of detecting and
quantifying impurities such as nitric acid in nitrogen dioxide gas mixtures. In principal
this would mean that measurements made on the transfer cylinders by FT-IR and
chemiluminescence should have shown a small bias in their results due to the nitric acid
impurities present in the transfer standards, assuming that all nitric acid in the
participants’ primary standards had been accounted for and that the nitric acid had not
been scrubbed from the transfer standard gas prior to measurement by
chemiluminescence. The magnitude of the bias that could be expected in these cases
would be in the order of 100 nmol/mol to 350 nmol/mol or 1% to 3.5 % respectively of
the nominal mass fraction of 10 µmol/mol. This level of bias was not observed, and
would have been similar in magnitude to the measurement uncertainties of both
techniques. Further interpretation of potential biases would require the nitric acid
impurity content of all primary standards used by participants to be evaluated. In the
case of measurements at the BIPM, a long pathlength FT-IR gas cell was used to
quantify nitric acid and correct for its presence. The NIST chemiluminescence
measurements were performed on a gas stream from the transfer standard that had been
scrubbed of its nitric acid content using nylon filters. The BIPM and NIST measurement
results agreed well within their measurement uncertainties and the reference value of
the comparsion, confirming the agreement of two independent methods for correcting
for the presence of nitric acid.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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1.50
1.20
0.90
0.60
CLD
D (μmol/mol)
0.30
CLD
CLD
CLD
UV
0.00
CLD
CLD
-0.30
-0.60
-0.90
-1.20
-1.50
NPL
SMU
NMISA
KRISS
NIST
CEM
VNIIM
Laboratory
CCQM-P110 B1 (FT-IR)
CCQM-K74
Figure 8. Difference between participant results and the reference values in this pilot study and in the key
comparison CCQM-K74. The error bars represents the expanded uncertainty at a 95% level of
confidence. The measurement techniques used by participants for CCQM-K74 were: NPL; UV
photometry. SMU, NMISA, KRISS, NIST, CEM and VNIIM; Chemiluminescence
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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10.
Conclusion
The results of this pilot study indicate good consistency for the measurements against
in-house standards by FT-IR spectroscopy. The level of agreement between participants
is very similar to that reported in CCQM -K74 for which CLD and UV methods were
used. In addition, the relative standard uncertainties attributed to the FT-IR
measurement results in this study reached similar values as those reported for the
chemiluminescence and UV absorption techniques in CCQM-K74. This confirms that
FT-IR can be operated as a comparison method when calibrated with appropriate
gas standards for nitrogen dioxide measurements at the μmol/mol level, and can
achieve similar measurement uncertainties to chemiluminescence and UV
absorption techniques.
The pilot study reported here addressed nitrogen dioxide at a relatively low amount
fraction, the measurement of which can be subject to spectral interference. This choice
was made in order to show the performance of FT-IR as a comparison method for a
compound at a low amount fraction, and under conditions where some spectral interface
is present. Very many measurements of standard gas mixtures are made at significantly
higher amount fractions, and in mixtures for which there is no significant spectral
interference. We expect the performance of FT-IR spectroscopy as a comparison
method under such conditions to be as good as is reported here, and in some cases
better.
An additional pilot study (CCQM-P110-B2) was conducted on the same gas mixtures in
parallel with this pilot study. The second study addressed FT-IR spectroscopy when
used to measure the gas mixtures with respect to reference spectra. The results of this
second study will be reported elsewhere.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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ANNEX 1- BIPM Value assignment procedure
1. Description of the facility
The BIPM-NO2 primary gas facility combines gravimetry with dynamic generation of
gas mixtures. The facility includes a magnetic suspension balance, a flow control
system for the dynamic generation of gas mixtures and a flow control system for
nitrogen dioxide gas standards in cylinders. Both, gas cylinder and dynamic sources of
NO2 mixtures are ultimately connected to a continuous gas analyzer ABB Limas 11
(AO2020), and to the spectrometer FT-IR Thermo-Nicolet Nexus (See Figure 9).
The operation and automation of the ensemble of instruments (NO2 FT-IR facility-ABB
Limas 11-FT-IR) is achieved through a LabView® programme developed by members
of the BIPM Chemistry Department. Through a graphical user interface the programme
facilitates the setting and monitoring of all relevant instrumental parameters, automated
control of complex procedures, the recording of mass measurements and NO2 analyser
readings and related data and the graphical real-time display of many of the instrument
readings.
Rubotherm System
Flow Control System for
Flow Control System for Rubotherm
1.
2.
3.
4.
5.
6.
7.
Zero air generator
Nitrogen Generator
Nitrogen Cylinders
molbloc (0-1000) mL/min
SAES Nitrogen purifier
Mass flow controller (0-100) mL/min
Mass flow controller (0-1000) mL/min
8
6
P
5
4
9
7
P
2
V
waste
1
3
Rubotherm System
P
8. Magnetic suspension balance
9. NO2 permeation tube
P
11
10
Flow Control System for NO2 Gas Standards
10. Mass flow controller (0-1000) mL/min
11. Multi position valve 16-position valve)
V
V
waste
P
Flow Control System for NO2 Gas
Figure 9: Schematic of the BIPM NO2 facility
The magnetic suspension balance.
The magnetic suspension balance (MSB; Rubotherm, Germany) as depicted in Figure
10 is central to the system. An electromagnet is suspended from the base of the
weighing pan. Below this electromagnet there is a long vertical glass vessel, the
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 27 of 76
measurement cell of the MSB. At the top of the glass vessel there is a permanent
magnet which is held suspended by the electromagnet attached to the balance.
Air buoyancy free basic
load compensation
Microbalance
Electromagnet
Glass Suspension Coupling
Permanent Magnet
Thermostating Chamber (for
Circulating Liquid)
Measuring Load Decoupling
Nitrogen Flow
Thermocouple
Permeation tube
Flange Connection
Mixing chamber
Nitrogen dioxide/ Nitrogen mixture
Figure 10: Schematic of the BIPM NO2 facility permeation tube chamber and magnetic suspension
balance.
The position of the permanent magnet is detected electronically and maintained by a
servo-control of the current of the electromagnet. An NO2 permeation tube is suspended
from the permanent magnet. Thus, the balance measures the mass of the permeation
tube without being mechanically in contact with it, since the balance and the weighing
load are separated by a layer of glass. The coupling between the permeation tube and
the balance is purely magnetic and the sensitive balance is protected from the highly
corrosive NO2 gas and the sometimes elevated temperatures and gas flows surrounding
the permeation tube. This facilitates continuous monitoring of mass loss of the
permeation tube, which is located in a temperature controlled environment by means of
a double glass wall jacket containing water circulating at a constant temperature
controlled by a remote thermostat. At constant temperature, the tube emits NO2 through
its permeable fluoropolymer membrane at a constant rate. The balance is a high
resolution comparator (model AT20, Mettler, USA) with range of (0 to 22 g) and 2 μg
resolution. The balance is configured with two mass pieces (see Figure 10) used to
perform an external calibration of the balance. The term external calibration is used to
distinguish it from the internal calibration of the balance performed with stainless steel
mass standards. The two external calibration mass pieces have nominally the same
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 28 of 76
volume but different mass, as one is made of titanium (Ti) and the other of stainless
steel (SS). Briefly, they are used to correct for an effect on the mass measurements
arising from changes in the density of the ambient atmosphere surrounding the balance
itself. Since it was important to know the mass difference of the Ti and SS pieces with a
small uncertainty, they were calibrated in mass and volume in collaboration with the
BIPM Mass Department.
The flow control system for the magnetic suspension balance
To generate primary mixtures using the MSB, a well characterized flow of NO2-free gas
(nitrogen) is required. Once the flow controls system receives a pre-selected gas it
delivers two well characterized flows to the balance.
The total gas flow is characterized by means of a molbloc®/molbox® facility3, which
was calibrated at the LNE. An electronic digital pressure controller is used to maintain
the pressure of the incoming gas entering the molbloc at about 2700 hPa that is the
optimal pressure to minimize the uncertainty of the molbloc flow measurement (~0.1
%).
The gas flow is then introduced to a gas purifier that removes the remaining water and
oxygen that may leak into the gas. The gas flow is then divided in two streams, a carrier
and a diluent, both regulated by two mass flow controllers (MFC’s).
The flow of the carrier stream is set at a constant value, 100 mL/min, mixing with the
NO2 emerging at constant rate from the permeation tube. The pressure conditions of the
permeation chamber are controlled by an electronic digital pressure to avoid any
buoyancy variation.
The gas mixture of the carrier line is afterwards diluted by a larger flow, the diluent
stream, varied within the range (0.3 to 5) L/min in order to, dynamically, generate
primary NO2 mixtures in nitrogen (or air) at various concentrations in the range (1-15)
μmol/mol.
Permeation tubes with permeation rates in the range (5000-10000) ng/min are used for
this purpose.
The flow control system for NO2 gas standards
The third module, namely the flow control system for NO2 gas standards, enables
comparison between the dynamically generated gas mixtures and cylinder standards of
NO2 in nitrogen contained in high pressure cylinders (and, alternatively, comparison
between various cylinder mixtures). This comparison is achieved via the response of
the NO2 analyser, whether ABB Limas 11 or FT-IR. The continuous gas analyzers
ABB Limas 11 (part of the AO2020 series) operates according to the NDUV (Non
Dispersive Ultraviolet Absorption) measurement principle. The measuring effect is
specific radiation absorption of the measured gas component in the UV spectra region to
detect NO2. The FT-IR analyser is a Thermo Nicolet Nexus model enclosed in an
isolation box fully described in Section 6.1.
3
A molbox® facility is a support unit for making gas flow measurements using molbloc mass flow
elements. The molbox® hardware reads calibration data off the molbloc® facility and measures molbloc®
upstream and downstream pressure using built-in high precision Reference Pressure Transducers (RPTs).
The key molbloc®L measurement is the differential pressure across the element, which is roughly
proportional to the mass flow rate through it. The molbloc® elements are calibrated to be used at an
absolute pressure which remains nearly constant, while the differential pressure varies with flow rate.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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The flow control system enables the sequential sampling of up to 15 standards
contained in cylinders by means of a 16 position valve (MPV-16). V2 is a 4-port 2position valve. It is used to select which sample stream, from either the MSB or from a
cylinder, is directed to the analysers, the other stream being directed to waste, without
perturbing the flow of either stream.
2. Measurement protocol of the BIPM
On receipt by the BIPM, all cylinders were allowed to equilibrate at laboratory
temperature for one week. All cylinders were rolled for 60 minutes to ensure
homogeneity of the mixture.
Each cylinder was connected to one inlet of a 16-inlet automatic gas sampler connected
to the FT-IR spectrometer and to the BIPM NO2 dynamic generation facility.
The pressure reducers of each cylinder were flushed nine times with the mixture. The
cylinder valves were then closed leaving the high pressure side of the pressure reducer
at the cylinder pressure and the low pressure side of the pressure reducer at ~300 kPa.
The cylinders were left to stand for at least 24 hours, to allow conditioning of the
pressure reducers.
Immediately prior to an analysis, each cylinder valve was opened again and the pressure
reducer flushed three times. The suite of cylinders was analysed sequentially.
For the FT-IR spectra acquisition 120 scans were co-added over a period of 2 minutes to
provide one single beam spectrum of a sample. This single beam spectrum was then
ratioed with a similar spectrum of ultra pure nitrogen collected under similar conditions
to provide an absorbance spectrum of the gas sample (relative to ultra pure nitrogen).
For each analyser, a calibration line was evaluated using the Generalised Least Squares
approach described by ISO 6143:20014.
The assigned BIPM nitrogen dioxide value was then equal to the predicted value from a
calibration line calculated from a set of dynamic nitrogen dioxide primary gas mixtures
obtained from the BIPM Nitrogen Dioxide (NO2) Primary Facility.
4
ISO 6143:2001: Gas analysis- Comparison methods for determining and checking the composition of calibration gas mixtures.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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3. BIPM measurement uncertainties and analyser response
The mole fractions of the dynamically produced gas mixtures obtained with the BIPM
facility was calculated by the expression below:
 P  Vm
x NO2  
 qv  M NO
2

  M HNO3  xHNO3

 
M NO2
 

M x 
    imp imp 

 M NO

2



(5)
where:
x NO 2 is the NO2 mole fraction in μmol/mol;
is the NO2 permeation rate in ng/min-1;
P
Vm = 22.4038 L/mol, is the molar volume of air/N2 at standard conditions
(273.15 K, 101.3 kPa);
M NO 2 = 46.0055 g/mol, is the molar mass of NO2;
qv is the total flow of N2 given by the sum of carrier nitrogen (qv molbloc2) and the
diluent nitrogen (Fmolbloc1 and) flows in Ml/min-1 at standard conditions (273.15
K, 101.325 kPa);
xHNO3 is the HNO3 mole fraction in μmol/mol measured by FT-IR spectroscopy;
M HNO3 = 60.005 g/mol is the molar mass of HNO3;
ximp are the mole fractions of the impurities in μmol/mol measured by FT-IR
Spectroscopy; and
M imp are the molar mass of the impurities;
Applying the uncertainty propagation law and assuming no correlation between the
input quantities the following uncertainty budget was developed:
 x NO2
u ( x NO2 )  
 P
2
2
2

 x
  u 2 ( P )   NO2

 Vm
2
2
 x

  u 2 (Vm )   NO2
 M NO


2
 x
 x NO 2 
 x NO 2 

  u 2 ( x HNO )  
  u 2 ( M HNO )   NO 2
3
3
 x

 M

 x
HNO 3 
 HNO 3 

 imp
2
2

 x
  u 2 ( M NO )   NO2
2
 q

v



 x
  u 2 ( ximp )   NO 2

 M
imp


2
2

  u 2 ( F ) 


  u 2 ( M imp )


(6)
The permeation standard uncertainty, considering a permeation device with a
permeation equivalent to P ≈ 8357 ng/min, was estimated u P   4.18 ng/min where
u P  is the probability that the value of P lies within the interval ±6.17 ng/min with
rectangular distribution.
The uncertainty in NO2 molar mass of 0.00047 g/mol, 0.001 % relative, can be derived
from the IUPAC Table of Atomic Weights.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 31 of 76
The molar volume Vm of a real gas at standard conditions (T = 273.15 K, p = 101.325
kPa) is given by the formula
Vm 
ZRT
p
(7)
where Z is the compressibility factor and R is the gas constant, 8.314 472 J/mol/K, with
relative u(R) of 1.8  10-6. Since they are defined by convention there is no uncertainty
in T and p.
The compressibility factor of nitrogen obtained from the NIST Refprop database is ZN2
= 0.9995434 with relative u(Z) of 15  10-6.
Thus the molar volume of nitrogen and its standard uncertainty are
VmN2
= 22.4037 L/mol
u(VmN2)
= 0.0003 L/mol, or 1.5  10-5 relative.
The BIPM measured the flow in its system by using molblocs. These were calibrated by
the LNE on 27 April 2009. The uncertainty of the BIPM’s flow measurements is
dominated by and based on calibration. The uncertainty in the flow measurements u(qv)
was taken from the LNE calibration certificate N° K20869/1. No additional component
for the stability of the flow instrument was added, since the time between calibration
and the first measurements were short, and no significant deviation between the first
and second series of BIPM measurement results was observed for stable cylinder gas
standards. The expanded relative uncertainty (k=2) quoted in the calibration certificate
is 0.2 % at the flows used in the comparison. In correspondence between the BIPM and
the LNE, the LNE confirmed the relative expanded uncertainties quoted in their CMCs,
comparison results and the calibration certificates to be as follows:
-
0.22 % to 0.40 % in LNE’s CMCs
0.19 % to 0.26 % in the Euramet comparison reference (2)
0.18 % to 0.27 % in the Calibration Certificate K20869/1.
The uncertainty in the calculated nitric acid mole fraction, xHNO3, obtained by FT-IR
spectroscopy, is given by:
u  x HNO 3  
0.022  0.015 x 2  0.05 x 2
(8 )
where x is the mole fraction of nitric acid predicted by FT-IR into the gas mixtures. A
future publication will give a detailed description of the measuring methodology and
quantification process by FT-IR for the determination of nitric acid.
As for NO2, the uncertainty in nitric acid molar mass, 0.000561 g/mol (0.0009 %
relative), was derived from the IUPAC Table of Atomic Weights.
It follows that the uncertainty budget for a NO2 mixture having a nominal concentration
of ~10.0 μmol/mol is as tabulated below in Table 8:
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 32 of 76
Quantity
Estimate
Assumed
distribution
Standard
uncertainty
Sensitivity
coefficient
u(xi)
ci=xNO2/x
Vm
qv molbloc1
MNO2
xHNO3
xN2O4
xN2O3
xN2O5
xHONO
x HO2NO2
MHNO3
8.3573
10−6·g/min
22.4038
L/mol
452
10−3·L/min
46.0055
g/mol
0.104
10−6 mol/mol
0
mol/mol
0
mol/mol
0
mol/mol
0
mol/mol
0
mol/mol
63.013
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Normal
4.18
10−9·g/min
340.00
10−6 L/mol
455.21
10−6 L/min
1.40
10−3 g/mol
0.021
10−6· mol/mol
866
10−12· mol/mol
307
10−12· mol/mol
361
−12
10 · mol/mol
520
10−12· mol/mol
572
10−12· mol/mol
1.17
10−3 g/mol
g/mol
Quantity
xNO2
Index
contribution
%
ui(y)
mol/mol
xi
P
Uncertainty
Value
Standard
Uncertainty
8.86
μmol/mol
30
μmol/mol
−2.3
4.5
10−9
140
10−12
−9.1
10−9
−270
10−12
−29
10−9
−1.7
10−9
−510
10−12
−850
10−12
−530
10−12
−980
10−12
−2.6
10−9
10−12
1.1
400
10−9
−20
10−6
−190
10−9
−1.4
−2.0
−1.7
−2.3
−1.0
1.7
2.2
0.0
8.8
0.0
88.5
0.3
0.0
0.0
0.0
0.1
0.0
Table 8. Uncertainty budget for a NO2 /N2 primary mixture generated with the BIPM facility.
The degrees of freedom were numerous, so a coverage factor k = 2 was assumed
appropriate for the expanded uncertainty. The main uncertainty contributors remain the
mole fraction determination of nitric acid and the gas flow measurements. Figure 11
illustrates the new uncertainties in xNO 2 for the dynamic generation of NO2 in nitrogen
mixtures over the mole fraction range (8-12) μmol/mol, using a permeation tube with
permeation rate of 8357 ng/min-1 and flows in the range (350-450) mL/min. The
uncertainty is almost a constant and can be fitted by a linear function of the mole
fraction. A least squares fit was made using the Excel LINEST function. The standard
uncertainties in xNO 2 can be modelled by the following linear function (numerical
values in µmol/mol):
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 33 of 76
u ( xNO2 )  0.001036x  0.020818
0.04
y = 0.0010367903x + 0.0208182092
R2 = 0.9999841982
0.038
u (x NO2) / (μmol/mol)
(9)
0.036
0.034
0.032
0.03
0.028
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
x NO2 / (μmol/mol)
Figure 11. Standard uncertainty of dynamically generated NO2 mixtures on the BIPM NO2 facility
over a range of xNO = (8-12) μmol/mol.
2
4. Covariance between two dynamically generated gas mixtures
Non-zero covariances, u ( xNO2 ,i , xNO2 , j ) were included in the uncertainty calculations
because all dynamic mixtures were derived from the same BIPM facility and an error in
the analyte content of the one gas is considered to propagate to all gas mixtures in a
positive correlated fashion. The covariance between two calibration gas mixtures i and j
is described as follows:
2
u ( xNO2 ,i , xNO2 , j )   u ( xNO2 ,i )  ,
(10)
Where u ( x NO 2 ,i ) is the standard uncertainty of the more concentrated mixture as given
by equation 10,

qj
(11)
qi
is the dilution factor of the total gas flows qj and qi (with qj < qi). Note that as the NO2
calibration gas mixtures generated with the facility are distributed in a small range of
mole fractions (typically 8 nmol/mol to 12 nmol/mol), the dilution factor is often close
to 1, and the covariances often close to the variances u(xNO2,i)2.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 34 of 76
5. FT-IR analysis of gas standards
Analysis of all gas standards was undertaken to quantify nitric acid within the gas
standards, and to compare these with the impurities and their uncertainties reported by
the participating laboratories.
6. FT-IR Spectra acquisition procedure
A ThemoNicolet Nexus FT-IR spectrometer was configured with a MCT-high D* liquid
N2-cooled mid-infrared detector and a 6.4 m pathlength multipass White cell (Gemini
Scientific Instruments, USA) for the purposes of quantitative analysis for gas reference
standards. The White cell has wetted surfaces of only electropolished stainless steel and
gold (mirror coatings) to minimise surface interactions with reactive gas phase species.
To keep the internal optical path of the spectrometer free of any interference species this
ensemble has been placed in stainless steel enclosure which is constantly purged with
ultra high purity nitrogen (dewpoint ~-95°C, i.e. ~200 nmol/mol-1 H2O) flowing at ~15
L/min-1.
The gas sample, from either the Rubotherm MSB or from a high pressure cylinder,
flows from the NO2 facility sampling manifold through the White cell, and then to
waste. The sample flow rate is controlled immediately downstream of the White cell at
~400 mL/min-1. The sample pressure and temperature are measured on real time by
means of a calibrated barometer (Series 6000 Digital Pressure Transducer, Mensor,
USA) and a calibrated 100 Ω RTD temperature probe attached to the White cell.
The spectrometer user interface is by means of the IMACC software. IMACC allows
the automatic setting of all instrument parameters into Thermo's proprietary Omnic
software for the control, spectra acquisition and on-line analysis.
For the acquisition of high quality spectra suitable for quantitative analysis, 120 scans
are co-added over a period of 2 minutes to provide one single beam spectrum of a
sample. This single beam spectrum was then ratioed with a similar spectrum of ultra
pure nitrogen collected under similar conditions to provide an absorbance spectrum of
the gas sample (relative to ultra pure nitrogen).
The White cell has a volume of ~750 mL and the sample flows at ~400 mL/min.
Assuming perfect mixing in the cell we estimate that an initial sample at time t = 0 s has
been 99.9 % replaced after 10 min of flow, and 99.9999 % replaced after 20 min.
Accordingly, to ensure complete exchange of sample, spectrum acquisition started at t =
0 but only the measured spectra obtained after flowing the sample through the White
cell for 35 min were used for the mole fraction determination. We also empirically
verified that after 30 min of flow, the sample was completely exchanged, within the
bounds of measurement uncertainty.
The absorbance spectra of gas reference standards obtained following this procedure
had a very high signal: noise ratio, with the level of noise in the baseline being typically
~2 × 10-4 abs10 peak-peak. By comparison the main NO2 peak had absorbance in the
range (0.04-0.16) abs10.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 35 of 76
As the FT-IR was calibrated with our permeation device, its sole contributing
uncertainty component is the type A uncertainty. From times series analysis the
uncertainty in the response of the FT-IR spectrometer was estimated in 20 nmol/mol for
2 min averaging time.
7. Quantitative analysis of nitric acid
The determination of nitric acid was assessed configuring the FT-IR facility with a
multi pass white cells with an optical path of (48±1.2) m. Spectra were analysed by a
non-linear least-square fitting of the measured absorption spectra with synthetic spectra
using the program MALT4.4. This program included the calculation of synthetic spectra
from the HITRAN database of infrared absorption line parameters using the core of the
program MALT (an acronym for Multiple Atmospheric Layer Transmission) software
developed at the University of Wollongong described in detail by Griffith in 1996(3).
The program convolved a stick spectrum calculated from the line parameters with the
temperature, pressure, path length, resolution and instrument line shape function
specified by the user. Spectra were calculated iteratively from an initial estimate of all
input parameters following a modified Levenberg-Marquart algorithm until a least
squares best fit to the measured spectrum was obtained. Gas concentrations in the
sample were iteratively adjusted during the fit. The quality of the fit could be improved
by choosing a proper spectra window of the measured spectrum. Spectra which had
been acquired across a total wavelength range of (1660-1850) cm-1 were fitted on
spectral windows according to the impurities of interest, in this case nitric acid.
8. Uncertainty budget
Table 9 below summarises the uncertainty sources and presents the final combined
uncertainty associated with the FT-IR/MATL/CLS measurements of nitric acid at a
mole fraction (x) ranging from 100 nmol/mol to 250 nmol/mol with a FT-IR white cell
with a 48 m optical path.
Type A
Stability
Type B
MALT
HITRAN
Combined uncertainty
μmol/mol
0.020
0.015x
0.05x
0.022  0.015 x 2  0.05 x 2
(12)
Table 9: uncertainty budget associated with the FT-IR spectrometer
used as an absolute method of quantification to determine the
concentration of HNO3 in nitrogen.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 36 of 76
9. Regression analysis
The procedure outlined in ISO 6143:2001 (Gas analysis-Comparison methods for
determining and checking the composition of calibration gas mixtures) was used
for the analysis of the data from the comparison. This required:
-
the determination of the analysis function x=G(y) which expressed
analyte contents in relation to corresponding measured responses;
-
the validation of the analysis function; and
-
the prediction of the mole fraction values from the measured responses
and comparison to VSL and NMI’s values.
10. Determination and validation of analysis functions
All calculations were performed with B_LEAST, a computer programme which
implemented the methodology of ISO 6143:2001, and takes into consideration
uncertainties in both axes for regression analysis.
Validation studies performed by the BIPM to be published shortly will confirm the
linearity of the FT-IR response in the xNO2 range (4.5-15.5) μmol/mol.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 37 of 76
ANNEX 2 - Measurement reports of participants
Centro Español de metrología (CEM)
B1-1. General information
Institute
CENTRO ESPAÑOL DE METROLOGÍA (CEM)
Address
CALLE ALFAR, 2
28760 TRES CANTOS (MADRID)
SPAIN
Contact person
TERESA E. FERNÁNDEZ VICENTE
Telephone
+ 34 918 074 751
Email*
[email protected]
Serial number of cylinder
received
930676 (D650059)
Cylinder pressure as received
≈ 95 bar
Fax
+ 34 918 074 807
B1-2. Results
Nitrogen dioxide mole fraction
Expanded uncertainty
x NO2 / μmol/mol
U ( x NO 2 ) / μmol/mol
10,62
0,89
Coverage factor
2
B1-3. Uncertainty Budget
The mathematical mode used to calculate the uncertainty in the composition of mixture analyzed is a linear
combination of the sources of uncertainty due to the instrument used and the repeatability of the measurements. This
leads to:
2
u  u r2  u zero
 u L2
where u r is the standard deviation of the mean of the results obtained along the period of measurements, from the
linear fit regression by means of the IFSS software; u zero is the largest uncertainty among the obtained uncertainties
due to the linear fit regression by means of the IFSS software, that doesn’t force zero point; and uL is the uncertainty
of the path length due to the influence of the temperature and the pressure in the cell and the path length itself.
Table 1 summarizes the uncertainties budget.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 38 of 76
Uncertainty
source
Assumed
distribution
ur
normal
Standard
uncertainty /
mol/mol
0,41
Sensitivity
coefficient
1
Contribution to
standard uncertainty /
mol/mol
0,41
u zero
rectangular
0,14
1
0,14
uL
normal
0,29
- 0,32
0,094
Combined standard uncertainty / mol/mol
Expanded uncertainty, k5 = 2 / mol/mol
Table 1. Detailed uncertainty budget.
0,45
0,89
B1-4. FTIR instrumentation and acquisition parameters
Spectrometer
FTIR
Manufacturer
PerkinElmer
Type
GXI
Serial number
55161
Gas cell
Manufacturer
Specac
Type
SC-24220 Tornado T-20
Optical path (m)
20 m
Operation software details
Name of the software used to control the spectrometer
Spectrum Software
Name of the software used to acquire spectra
Spectrum Software
Name of the software used to analyse spectra
IFSS (Imacc
Software)
B1-5. Description of the procedure used during the gas analysis
Upon arrival the sample cylinder was rolled and stored in the laboratory under laboratory reference conditions. A
pressure reducer was connected to the sample cylinder. The reducer was carefully flushed as prescribed in
International Standard ISO 16664:2004 (Gas analysis – Handling of calibration gases and calibration gas mixtures –
Guidelines).
The sample cylinder was connected to a vacuum tree system connected to the FTIR. When the vacuum in the cell
was 4·10-4 kPa and the vacuum in the tree was 5·10-6 kPa, 16 background scans were collected. With the pressure
in the cell set next to 102,3 kPa, 100 scans were collected.
Due to the fact that the system lacks a sensor for the measurement of the temperature inside the gas cell, the
experimental temperature corresponds to the environmental conditions in the laboratory, next to 293 K.
5
The coverage factor shall be based on approximately 95 % confidence.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 39 of 76
The sample results reported come from the data obtained along three consecutive working days, from February the
16th to the 18th.
Three standards were used with the compositions specified in Table 2:
Species
Nitrogen Dioxide
Oxygen (not certified)
Nitrogen
Amount Fraction
Amount Fraction
NPL1272 / mol/mol
NPL1273 / mol/mol
(5,01 ± 0,10)
(10,00 ± 0,15)
13
22
Balance
Balance
Table 2. Primary reference gas mixtures used.
Amount Fraction
NPL1274 / mol/mol
(15,01 ± 0,22)
33
Balance
All mixtures were prepared gravimetrically and analysed by Non-Dispersive Ultraviolet (NDUV) technique.
Protocol B1 and B2 were carried out simultaneously.
B1-6 Complementary information on the cylinder
The value of the pressure left in the cylinder before shipment to the BIPM was 65 bar approximately.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 40 of 76
Korea Research Institute of Standards and Science (KRISS)
General information
Institute
KRISS
1 Korea Research Institute of Standards and Science
(KRISS), P.O.Box 102, Yusong, Daejeon, Republic of Korea
Address
Contact person
Lee, Jeongsoon for P110 B1 and b2
Oh, Sanghyup for K74
Telephone
+82-42-868-5766
Email*
[email protected]
Serial number of cylinder
received
D650044
Cylinder pressure as received
About 65 bar
Fax
+82-42-868-5042
Results
Cylinder No.: D650044
Nitrogen dioxide mole fraction
Expanded uncertainty
x NO2 / μmol/mol
U ( x NO 2 ) / μmol/mol
10.47
0.32
Coverage factor
k=2
Uncertainty Budget
Please provide a complete uncertainty budget.
Uncertainty
Standard uncertainty
factor
Gravimetry uncertainty (PRM)
μmol/mol
0.15
Analysis uncertainty
0.05
Total uncertainty
0.16
FTIR instrumentation and acquisition parameters
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 41 of 76
Spectrometer
Manufacturer
Bruker
Type
TENSOR 27
Serial number
T27. 1501
Gas cell
Manufacturer
OTSUKA
Type
MULTI PASS CELL
Optical path (m)
9.617
Software
Name of the software used to control the
FTIR COLLECTION MANAGER (FCM)
OPUS
spectrometer
Name of the software used to acquire spectra
FCM
Name of the software used to analyse spectra
FCM
Description of the procedure used during the gas analysis
Please describe in detail the analytical method(s) used for gas analysis and gas standards used for
calibration6.
We carried out ABA measurement in sequence to acquire the BIPM sensitivity
comparable to that of the PRM (A) which was prepared with gravimetry by KRISS.
Calibration of our FTIR analyzer was conducted at one point with PRM (A) cylinder with
0.30 ppm uncertainty (k = 2).
Gas from cylinder was introduced as:
Cylinder >> regulator >> MFC >> gas Cell >> vent to atmosphere or Vacuum during
pumping
Followings are the procedures to acquire the spectrum;
VACUUM less than 1.0 mb >> GAS CELL FILL with N2 TILL 1013 mb >> measurement
BG >> VACUUM less than 1.0 mb >> GAS CELL FILL with NO2 TILL 1013 mb >>
measurement PRM (A) >> VACUUM less than 1.0 mb >> GAS CELL FILL with NO2 TILL
1013 mb >> measurement BIPM sample (B) >> VACUUM less than 1.0 mb >> GAS CELL
FILL with NO2 TILL 1013 mb >> measurement PRM (A)
B1-6 Complementary information on the cylinder
Please report the value of the pressure left in the cylinder before shipment to the
BIPM:
6
The choice of the procedure used for gas analysis is the responsibility of the participating laboratory.
Nevertheless, for a proper evaluation of the data, it is necessary that the calibration method, as well as
the way in which the calibration mixtures have been prepared is reported to the co-ordinators..
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 42 of 76
PRESSURE LEFT: 52 BAR
If any other component other than NO2, nitrogen and oxygen was detected and/or
quantified please report its mole fraction in the table below: N.A.
Component
Mole fraction /
nmol/mol
Expanded uncertainty
Coverage factor
Measurement
technique
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 43 of 76
National Measurement Institute Australia (NMIA)
General information
Institute
NMIA – National Measurement Institute Australia
Address
Bradfield Road
Lindfield NSW 2070 AUSTRALIA
Contact person
Damian Smeulders
Telephone
+61 2 84673534
Email*
[email protected]
Serial number of cylinder
received
930662
Cylinder pressure as received
100 bar
Fax
+61 2 8467 3752
Results
Nitrogen dioxide mole fraction
Expanded uncertainty
x NO2 / μmol/mol
U ( x NO 2 ) / μmol/mol
10.74
0.63
Coverage factor
2
Uncertainty Budget
Combined standard uncertainty: u = 0.32 μmol/mol
Expanded uncertainty: U = 0.63 μmol/mol
Contributions to uncertainty:
Gravimetric uncertainty: 0.018
Mixture stability and conversion to NO2: 0.075
Instrument contributions:
Repeatability: 0.30
Resolution: 0.020
Difference due to spectral regions: 0.050
FTIR instrumentation and acquisition parameters
Spectrometer
Manufacturer
Thermo Nicolet
Type
6100
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 44 of 76
Serial number
AHR0701025
Gas cell
Manufacturer
Thermo Nicolet
Type
Nickel plated aluminium. KBr windows
Optical path (m)
10
Operation software details
Name of the software used to control the spectrometer
Omnic
Name of the software used to acquire spectra
Omnic
Name of the software used to analyse spectra
Excel
Description of the procedure used during the gas analysis
A Nicolet FTIR was used to acquire the spectra of the standards and unknown sample. The spectra were run at
resolutions of 0.5cm-1 and 0.25cm-1 with an aperture setting of 2. 100 scans were obtained for each analysis. The
background spectra was collected on the evacuated cell. Spectra were collected on a static gas sample with a
temperature of 60ºC at a pressure of 650 Torr.
The strong bands in the region 1530-1670 cm-1 and the weaker bands in the region 2840-2940 cm-1 were both used
for quantitation. The analyses of the standards and sample were repeated three times at each resolution with
evacuation and flushing of the cell between tests. The analysis procedure was repeated on several occasions over a
two week period.
Four closely bracketed calibration standards containing NO2 over the concentration range 8-12 µmol/mol were used
to determine the concentration of NO2 in the cylinder from the BIPM. Standards were made in uncoated, but
passivated 5L Luxfer aluminium cylinders with SS valves. Standards were manufactured from nitrogen oxide that
was converted to nitrogen dioxide in the presence of oxygen. Oxygen in the final mixtures was present at
approximately 1000 µmol/mol.
B1-6 Complementary information on the cylinder
Please report the value of the pressure left in the cylinder before shipment to the
BIPM:
78 bar
If any other component other than NO2, nitrogen and oxygen was detected and/or
quantified please report its mole fraction in the table below:
Component
Mole fraction /
nmol/mol
Expanded uncertainty
Coverage factor
Measurement
technique
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 45 of 76
National Metrology institute of Japan (NIMJ)
General information
Institute
National Metrology institute of Japan
Address
305-8563
1-1-1 Umesono, Tsukuba Ibaraki
Contact person
Nobuyuki Aoki
Telephone
+81-29-861-6824
Email*
[email protected]
Serial number of cylinder
received
APEX930760
Cylinder pressure as received
10MPa
Fax
+81-29-861-6854
Results
Nitrogen dioxide mole fraction
Expanded uncertainty
x NO2 / μmol/mol
U ( x NO 2 ) / μmol/mol
10.44
0.11
Coverage factor
2
Uncertainty Budget
Nitrogen dioxide mol fraction was estimated from calibration curve obtained by
measuring four primary standards. Calibration curve was regression line (x =G=b0 +b1y)
and calculated according to the Deming's generalized least-squares method. The
standard uncertainty of the analyte content, u(x) using the propagation of uncertainty on
the measured response and on the parameters of the analysis function, as follows.
2
2
2
 G  2
 G  2
 G  2
G G
 u b0   
 u b1   2
 u  y   
u  x   
u b0 , b1 
b0 b1
 y 
 b1 
 b0 
2
u(y): the standard uncertainty of the response y
u(b0), u(b1): the variance of the parameter b0 and b1 of the analysis function
u(b0, b1): the covariance of the parameters b0 and b1 of the analysis function
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 46 of 76
Table 1. Parameter of the Deming's generalized least-squares method
Parameter
Value
b0
-0.2802
b1
7234
u(y)
0.000006360
0.08312
u(b0)
39.55
u(b1)
u(b0, b1)
-3.217
FTIR instrumentation and acquisition parameters
Spectrometer
Manufacturer
JASCO Corporation
Type
FTIR-6100
Serial number
Gas cell
Manufacturer
JASCO Corporation
Type
10cm gas cell
Optical path (m)
10cm
Software
Name of the software used to control the spectrometer
Spectra Manager™
Name of the software used to acquire spectra
Spectra Manager™
Name of the software used to analyse spectra
Spectra Manager™
Description of the procedure used during the gas analysis
Calibration standards:
Four calibration standards were used for the determination of nitrogen dioxide
concentration in nitrogen. The standards were prepared from pure nitrogen dioxide, pure
nitrogen, and pure oxygen in accordance with ISO6142:2001 (Gas analysis-Preparation
of calibration gases-Gravimetric method. Pure nitrogen dioxide was from Sumitomo
Seika Chemicals Company Limited and pure nitrogen and oxygen from Japan Fine
Products. Two-step dilution was used to make the mixtures, with nitrogen dioxide
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 47 of 76
concentration of (2000~4000) mol/mol, and (9~18) mol/mol. Oxygen was added in
the first-step dilution. Table 2 shows characteristics of the calibration standards.
Table 2. Gravimetric value and expanded uncertainty in calibration standards
Gravimetric value of Gravimetric Value of Expanded uncertainty
O2
NO2
Cylinder number
[k=2]
(mol/mol)
(mol/mol)
(nmol/mol)
YAO02853
YA1387
YA1389
YA1393
1026.861
1233.577
1364.345
1738.478
9.711
11.944
16.659
17.435
0.023
0.020
0.043
0.027
Instrument calibration:
The following measurement cycle was repeated 7 times for the determination of
nitrogen dioxide concentration in air:
STD1 - STD2 – sample – STD3 – STD4
The response (yi) to analyte content in each cycle was the mean value of five individual
responses.
1 5
yil   yil, j
5 j 1
Calibration data ( y STD1 , y STD2 , y STD3 , ySTD 4 , y sample ) were obtained from the mean value of
seven cycles response ( yi1 , yi2 , yi3 •••, yi7 ).
 y 
7
yi 
l 1
1
i
7
The calibration data was used in order to determine the concentration of nitrogen
dioxide in synthetic air. The determination process was according to ISO 6143 using the
Deming’s generalized least-square method. The four calibration standards listed in table
2 were used for instrument calibration.
Sample handling:
The sample cylinder was stood at room temperature after arrival. Samples were
transferred to a gas cell with a stainless steel pressure regulator. the regulator was
evacuated before samples were introduced to gas cell. in addition, the measurement was
performed about ten minutes after sample introduction to the gas cell.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 48 of 76
National Institute of Standards and Technology (NIST)
General information
Institute
National Institute of Standards and Technology
Address
100 Bureau Drive,
Gaithersburg, MD 20899-8393, USA
Contact person
Franklin R. Guenther, Lyn Gameson
Telephone
301-975-3939
Email*
[email protected]
Serial number of cylinder
received
APEX930697
Cylinder pressure as received
8.0 Mpa
Fax
301-977-8392
Results
Nitrogen dioxide mole fraction
Expanded uncertainty
x NO2 / μmol/mol
U ( x NO 2 ) / μmol/mol
10.30
0.20
Coverage factor
2
Uncertainty Budget
Please provide a complete uncertainty budget.
Uncertainty Source,
XI
Certified working
standard
Instrument
Reproducibility
Change in gas matrix Non‐linear Cell pressure Cell temperature Assumed
Distribution
Standard
Uncertainty
(% Relative),
u(xi)
Sensitivity
Coefficient,
cI
Gravimetric
Standard or
Analytical
Component
Gaussian
0.50
1
Analytical
Gaussian
0.27
1
Analytical
Gaussian
Gaussian
Gaussian
Gaussian
0.50
0.50
0.04
0.17
1
1
1
1
Analytical
Analytical
Analytical
Analytical
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 49 of 76
FTIR instrumentation and acquisition parameters
Spectrometer
Manufacturer
Nicolet
Type
Nexus 670 (MCT Detector)
Serial number AEQ9900262
Gas cell
Manufacturer
Specac
Type
Cyclone 10C (Quartz)
Optical path (m) 10
Software
Name of the software used to control the spectrometer
OMNIC V7.1
Name of the software used to acquire spectra
OMNIC V7.1
Name of the software used to analyse spectra
In-House
Description of the procedure used during the gas analysis
Please describe in detail the analytical method(s) used for gas analysis and gas standards used for
calibration7.
FTIR Collection Parameters:
Parameter
Value
Number of Scans 512
Apodization
Boxcar
Resolution
0.125 cm-1
Standard used (in balance air):
Cylinder#
NOx (µmol/mol)
HNO3 (µmol/mol)
AAL069155 9.263 ± 0.050 0.403 ± 0.071
NO2 (µmol/mol
8.860 ± 0.087
FTIR Response – summation of the following NO2 peak areas:
Start (cm-1)
7
End (cm-1)
The choice of the procedure used for gas analysis is the responsibility of the participating laboratory.
Nevertheless, for a proper evaluation of the data, it is necessary that the calibration method, as well as
the way in which the calibration mixtures have been prepared is reported to the co-ordinators..
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 50 of 76
1601.256
1603.125
1606.741
1615.359
1623.916
1625.483
1626.990
1631.570
1632.956
1602.100
1603.908
1607.584
1616.202
1624.398
1625.905
1627.472
1632.354
1633.800
Analytical methodology:
Sample flow (200 mL/min) through the gas cell was controlled by a needle
valve. Each sample was purged through the cell for 60 minutes followed by coadding 512 scans (total collection time was 50 minutes). At least two spectrums
were collected per sample. The cell pressure (measured by Mensor Series
6000 Pressure Transducer, Serial# 0017125001) was auto collected every
minute throughout the FTIR acquisition; cell temperature was monitored
manually.
The nine NO2 FTIR peaks above were identified as being well formed and free from
water interference. They were summed to give a raw instrument response. The cell
temperature and pressure were averaged for each spectrum acquired. Using the standard
gas equation, a ratio was calculated for converting these cell conditions to standard
temperature (25oC) and pressure (760 mm Hg). The normalized FTIR response was
achieved by multiplying the raw response by this ratio.
B1-6 Complementary information on the cylinder
Please report the value of the pressure left in the cylinder before shipment to the
BIPM: 6.1 MPa
If any other component other than NO2, nitrogen and oxygen was detected and/or
quantified please report its mole fraction in the table below:
Component
Mole fraction /
nmol/mol
Expanded uncertainty
Coverage factor
Measurement
technique
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 51 of 76
National Physical Laboratory (NPL)
General information
Institute
National Physical Laboratory (NPL)
Address
Hampton Road, Teddington, Middlesex, TW11 0LW, UK
Contact person
Alice Harling / Martin Milton
Email*
[email protected] / [email protected]
Serial number of cylinder
received
D65 0042
Cylinder pressure as received
80 bar
Results
Nitrogen dioxide mole fraction
Expanded uncertainty
x NO2 / μmol/mol
U ( x NO 2 ) / μmol/mol
10.32
0.14
Coverage factor
K=2
Uncertainty Budget
Source of uncertainty
Gravimetric preparation
of standard
Drift in gravimetric value
of standard
Repeatability of
measured area
Interference of HNO3 in
analyser
Cell pressure
Cell temperature
Estimation
Method
Standard
uncertainty
Nominal value
Relative standard
uncertainty
A
13 nmol/mol
10000 nmol/mol
0.13%
B
10 nmol/mol
10000 nmol/mol
0.10%
A
0.35%
0.35%
B
0.5%
0.50%
B
B
1 mbar
0.5K
1050 mbar
298 K
Combined
uncertainty
0.1%
0.2%
0.67%
The expanded uncertainty (k=2) is 1.4 %.
Note: since the optical path –length of the cell remained unchanged during the
experiment, it is not incorporated as a source of uncertainty.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 52 of 76
FTIR instrumentation and acquisition parameters
Spectrometer
Nicolet 6700
Manufacturer
Thermo Scientific
Type
6700
Serial number
AHRO901995
Gas cell
Manufacturer
Specac
Type
Cyclone C5
Optical path (m)
8m
Software
Name of the software used to control the spectrometer
OMNIC
Name of the software used to acquire spectra
OMNIC
Name of the software used to analyse spectra
OMNIC
Description of the procedure used during the gas analysis
Please describe in detail the analytical method(s) used for gas analysis and gas standards used for
calibration8.
Calibration Standards
Gravimetric standards were prepared to compare against the unknown (D6500042).
Standard A (NPL1275R) contains 10.001 ppm NO2 in N2. Standard B (NPL1126R2)
contains 9.9994 ppm NO2 in N2.
Parents
Daughter
pure NO + N2
50 mmol/mol NO/N2
74R2
4000 mol/mol NO2/N2
464R
4000 mol/mol NO2/N2 + N2
800 mol/mol NO2/N2
1206R2
800 mol/mol + 9% O2/N2 + N2
100 mol/mol NO2/N2
1117R4
50 mmol/mol NO/N2 + 9% O2/N2 + N2
8
The choice of the procedure used for gas analysis is the responsibility of the participating laboratory.
Nevertheless, for a proper evaluation of the data, it is necessary that the calibration method, as well as
the way in which the calibration mixtures have been prepared is reported to the co-ordinators..
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 53 of 76
100 mol/mol NO2/N2 + N2
10 mol/mol NO2/N2
1275R
FTIR Acquisition Conditions
The system was setup to identify the optimum resolution, path length and pressure
necessary for this analysis. The optimised conditions chosen for the measurement were
Detector
No of scans / Scan time
Apodisation
MCT (liquid N2 cooled)
64
Happ-Genzel
-1
Nominal Resolution
True Resolution (“Data point Spacing”)
Path length
Temperature of gas cell
0.5 cm
-1
0.241 cm
8m
298K
Measurement Procedure
1. The gas cell was evacuated to 5 x 10-4 mbar, and the FTIR system purged with
Metrology Grade nitrogen for several hours.
2. The gas cell was filled with BIP N2.
3. When the pressure in the cell (indicated on the Baratron pressure gauge) reached
1050 mbar, the exhaust to the cell was opened and the BIP N2 left to flow
through and flush the cell. During this time the reduction in carbon dioxide in
the background spectrum was monitored.
4. After 10 minutes the background was collected (over 64 scans)
5. The BIP N2 was stopped and the gas line and regulator from the FTIR system to
the cylinder to be measured were purged and evacuated.
6. The gas cell was then re-evacuated to 5 x 10-4 mbar.
7. The sample was allowed to flow into the gas cell until the pressure read ~1050
mbar, then the exhaust was opened and the sample flowed through the cell
during the measurements.
8. Five consecutive measurements were made for each sample (over 64 scans),
using the same background.
Results and spectroscopy
The nitrogen dioxide peak at 1600 cm-1 was used for the measurements. The results
from a second peak at 2860 to 2940 cm-1 are also given for information.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 54 of 76
The samples were run in the following sequence on 9th Dec 2009:
Background
Standard NPL 1275R
Background
Unknown D6500042
Background
Standard NPL 1126R2.
The integration of the peak areas was carried out using the Thermo Scientific software
OMNIC. The results were validated using a MATLAB code developed at NPL.
The value of the unknown was calculated by means of a ratio of the FTIR response
against one of the standards. In each case, the area counts given in the table are after
background subtraction.
The result given is the mean of the analysis carried out against the two standards.
Results of analysis 9/12/2009
Run #
Matrix
1
2 Air
3
4 Air
5 Air
6 Air
7 Air
8
9 N2
10 N2
11 N2
12 N2
13 N2
14
15 N2
16 N2
17 N2
18 N2
19 N2
Cylinder
NPL1275R
NPL1275R
NPL1275R
NPL1275R
NPL1275R
AV
%STDEV
D650042
D650042
D650042
D650042
D650042
AV
%STDEV
NPL1126R2
NPL1126R2
NPL1126R2
NPL1126R2
NPL1126R2
AV
%STDEV
AREA COUNTS using
Modified area counts
OMNIC software
(taking into account pressure )
NO2 (1)
NO2 (2)
NO2 (1)
NO2 (2)
Grav conc (ppm) File name
Pressure (mbar) Temperature (K) 2940- 2860 cm-1 1600cm-1
2940- 2860 cm-1
1600cm-1
BKG_1
1060.94
298
10.001
NPL1275R_091209_1
1056.44
298
0.26499
5.17367
0.264879633 5.171515202
BKG_2
1056.18
298
10.001
NPL1275R_091209_2
1056.48
298
0.30192
5.14157
0.301782826 5.139233985
10.001
NPL1275R_091209_3
1056.5
298
0.27151
5.16044
0.271381505 5.157997766
10.001
NPL1275R_091209_4
1056.47
298
0.2958
5.12761
0.295668405
5.12532884
10.001
NPL1275R_091209_5
1056.45
298
0.30739
5.15958
0.307259066 5.157382252
0.2883
5.1526
0.2882
5.1503
6.56%
0.35%
6.56%
0.35%
BKG_3
1055.88
298
D650042_091209_1
1055.93
298
0.28779
5.34295
0.287809078 5.343304196
D650042_091209_2
1055.99
298
0.33703
5.32353
0.337033192 5.323580413
D650042_091209_3
1055.99
298
0.34953
5.30406
0.34953331 5.304110228
D650042_091209_4
1056.01
298
0.38034
5.32393
0.380336398 5.323879584
D650042_091209_5
1056.01
298
0.3795
5.31062
0.379496406 5.310569711
0.3468
5.3210
0.3468
5.3211
10.96%
0.28%
10.96%
0.28%
BKG_4
1055.82
298
9.9994
NPL1126R2_091209_1
1055.96
298
0.28632
5.14463
0.286330846
5.14482488
9.9994
NPL1126R2_091209_2
1055.95
298
0.31271
5.1932
0.312724807 5.193445902
9.9994
NPL1126R2_091209_3
1055.95
298
0.28366
5.16915
0.283673432 5.169394763
9.9994
NPL1126R2_091209_4
1055.98
298
0.26799
5.15368
0.267995076 5.153777609
9.9994
NPL1126R2_091209_5
1055.98
298
0.29884
5.17311
0.29884566 5.173207977
0.2899
5.1668
0.2899
5.1669
5.80%
0.36%
5.80%
0.36%
Standard
NPL1275R
NPL1126R2
Calculated conc of D650042 (ppm)
NO2 (1)
NO2 (2)
12.04
10.33
11.96
10.30
Note: the “modified area counts” are corrected from the measured pressure to a standard
pressure of 1056 mbar.
B1-6 Complementary information on the cylinder
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 55 of 76
Please report the value of the pressure left in the cylinder before shipment to the BIPM:
40 bar
If any other component other than NO2, nitrogen and oxygen was detected and/or
quantified please report its mole fraction in the table below:
Component
Mole fraction /
nmol/mol
Expanded uncertainty
Coverage factor
Measurement
technique
HNO3
190
38 nmol/mol
K=2
FTIR (library spectra)
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 56 of 76
National Metrology Institute of South Africa (NMISA)
General information
Institute
National Metrology Institute of South Africa (NMISA)
Address
CSIR, Building 5
Meiring Naudé Road
Brummeria, 0184
Pretoria
South Africa
Contact person
A Botha
Telephone
+27(0)12 841 3800
Email*
[email protected]
Serial number of cylinder
received
D650032
Cylinder pressure as
received
96 bar
Fax
+27(0)86 509 2485
Results
Nitrogen dioxide mole
fraction
Expanded uncertainty
x NO2 / μmol/mol
U ( x NO 2 ) / μmol/mol
10,62
0,22
Uncertainty Budget
Parameter
Temperature
Pressure
Verification
Stability
Gravimetry
Bias
Coverage
factor
2
Standard uncertainty(u)
0,11% rel
0,09% rel
0,18% rel
0,10% rel
0,13% rel
1% rel
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 57 of 76
FTIR instrumentation and acquisition parameters
Spectrometer
Manufacturer
Nicolet Instrument Corporation
Type
Magna IR 560 E.S.P
Serial number: ADU9900836
Gas cell
Manufacturer
Gemini Scientific Instruments
Type
Gemini-Mars
Optical path (m):10
Software
Name of the software used to control the spectrometer
Omnic version 8
Name of the software used to acquire spectra
Omnic version 8
Name of the software used to analyse spectra
Malt5 version 5.2
Description of the procedure used during the gas analysis
After the arrival of D65 0032 cylinder in the laboratory, the cylinder was stabilised at
room temperature (22 ºC ± 2 ºC) and humidity of (50 % ± 10%) before checking the
pressure and doing measurements. The standards and sample were transferred directly
to the FTIR using a system composed of pressure regulator, mass flow controller and
control valves.
The measurements of D65 0032 received from the coordinator (BIPM) were made
during January 2010 by direct comparison with four gravimetric preparation standards
by NMISA containing 10 μmol/mol concentrations. The results reported all follow from
a “bracketing” comparison strategy.
For FTIR measurements a NICOLET-Magna-IR-560 was used. A fixed optical path
length gas cell of 10 m from Gemini-Mars was used. Measurement conditions: 0.5 cm-1
resolution, 64 scans, phase correction (Mertz), Happ-Genzel apodization, water
correction performed by the OMNIC-Software, zero level of zero-filling, liquid nitrogen
cooled mercury cadmium telluride (MCT/A) detector. Nominal measurement pressure
for all samples: 109.5 kPa. The optical bench set up was continuously purged with
BIPTM + N2 (6.0).
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 58 of 76
For every measurements of cylinders a fresh Background BIPTM + N2 (6.0) was used.
Cylinders were measured randomly at continuous flow (i.e 1000 ml/min) controlled by
mass flow controller. The quantification was performed by MALT version 5.2 software.
B1-6 Complementary information on the cylinder
Please report the value of the pressure left in the cylinder before shipment to the BIPM:
23 bar
If any other component other than NO2, nitrogen and oxygen was detected and/or
quantified please report its mole fraction in the table below:
Component
HNO3
Mole fraction / Expanded uncertainty /
nmol/mol
nmol/mol
150
15
Coverage
factor
Measurement
technique
2
FTIR
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 59 of 76
Slovak Institute of Metrology (SMU)
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 60 of 76
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 61 of 76
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 62 of 76
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 63 of 76
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 64 of 76
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 65 of 76
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 66 of 76
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 67 of 76
Mendeleyev Institute for Metrology (VNIIM)
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 68 of 76
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 69 of 76
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
Page 70 of 76
Federal Institute for Materials Research and Testing (BAM)
General information
Institute
Address
BAM Federal Institute for Materials Research and Testing
Unter den Eichen 87
12205 Berlin
Germany
Contact person
Dirk Tuma
Telephone
+49 30 8104 4113
Email*
[email protected]
Serial number of cylinder
received
930722 TC1
Cylinder pressure as received
98 bar
Fax
+49 30 8104 3207
Results
Nitrogen dioxide mole fraction
Expanded uncertainty
x NO2 / μmol/mol
U ( x NO 2 ) / μmol/mol
10.53
0.75
Coverage factor
2
Uncertainty Budget
Please provide a complete uncertainty budget.
Three terms go with the calculation of U: umeas = standard deviation from the measurement (three
scans) of the sample; ucal = standard deviation from the measurement of the two calibration
gases (three scans for each calibration gas, the value for ucal is the arithmetic mean); uintrinsic = an
intrinsic uncertainty of the calibration gas of 2 % (considers stability)


U x NO 2 
u meas 2  u cal 2  u intrinsic 2
FTIR instrumentation and acquisition parameters
Spectrometer
Manufacturer
Thermo Nicolet Corporation
Type
Nexus 470
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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Serial number
AES 0300879
Gas cell
Manufacturer
Thermo Electron Corporation
Type
25 by 4 mm KBr sample windows
Optical path (m)
10
Software
Name of the software used to control the spectrometer
OMNIC 6.2
Name of the software used to acquire spectra
OMNIC 6.2
Name of the software used to analyse spectra
OMNIC 6.2
Description of the procedure used during the gas analysis
Please describe in detail the analytical method(s) used for gas analysis and gas standards used for
calibration9.
Prior to the analysis, the cell was evacuated and flushed with dry nitrogen to remove any
impurities that absorb infrared energy. A 10-m gas cell was employed.
Background was collected in the evacuated cell. Subsequently, the gas pressure was adjusted to
a constant pressure of 100 kPa, and several test runs provided identical spectra.
Sample spectra of each gas were recorded three times maintaining equal conditions. For each
measurement, a new gas portion was loaded from the cylinder. A background scan was done
before each sample scan. The analysis resorted to the area below the first overtone, i.e.,
approximately between 2800 and 2950 cm–1.
Two calibration gases were employed; x(cal. sample # 1) = 12.28 µmol/mol, x(cal. sample # 2) =
9.43 µmol/mol. The NO2 mole fraction of the test sample was calculated via linear interpolation.
Date of analysis: 02-06-2010
B1-6 Complementary information on the cylinder
Please report the value of the pressure left in the cylinder before shipment to the
BIPM:
Cylinder pressure: 87 bar
9
The choice of the procedure used for gas analysis is the responsibility of the participating laboratory.
Nevertheless, for a proper evaluation of the data, it is necessary that the calibration method, as well as
the way in which the calibration mixtures have been prepared is reported to the co-ordinators..
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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If any other component other than NO2, nitrogen and oxygen was detected and/or
quantified please report its mole fraction in the table below:
Component
Mole fraction /
nmol/mol
Expanded uncertainty
Coverage factor
Measurement
technique
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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Bureau International des Poids et Mesures (BIPM)
A1.
General information
Institute
Bureau International des Poids et Mesures (BIPM)
Address
92312 Sèvres Cedex, France.
Contact person
Edgar Flores
Telephone
+ 33 1 45 07 70 92
21
Email*
[email protected]
Serial number of cylinder
received
930697
Cylinder pressure as
received
11MPa
A2.
Fax :+ 33 1 45 34 20
Results
The BIPM result is given in the following table:
Nitrogen dioxide mole fraction
Expanded uncertainty
x NO2 / μmol/mol
U ( x NO 2 ) / μmol/mol
10.343
0.048
Coverage factor
2
Note: In the version Draft A of this report erroneously the preliminary result 10.329
μmol/mol was reported as the nitrogen dioxide mole fraction of the standard 930697
being the correct value, 10.343 μmol/mol, used in all calculations of this report.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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A3.
Uncertainty Budget
Please provide a complete uncertainty budget.
The uncertainty budget of the BIPM-NO2 facility is presented in section 3 of ANNEX 1.
A4.
Description of the procedure used during the gas analysis
Please describe in detail the analytical method(s) used for gas analysis10.
The method used for the analysis of the cylinder was based on primary reference
mixtures generated by the BIPM-NO2 facility. The BIPM-NO2 facility comprises a
magnetic suspension balance, a flow control system for the dynamic generation of the
gas mixtures and a flow control system for static nitrogen dioxide gas standards. Both,
static and dynamic sources of NO2 mixtures are ultimately connected to a continuous
gas analyzer ABB Limas 11 (AO2020), and to a FT-IR spectrometer. The operation and
automation of the ensemble of instruments (NO2 FT-IR facility-ABB Limas 11-FT-IR)
is achieved through a LabView® programme. Through a graphical user interface the
programme facilitates the setting and monitoring of all relevant instrumental
parameters, automated control of complex procedures, the recording of mass
measurements and NO2 analyser readings and related data to file and the graphical realtime display of many of the instrument readings.
Nnitric acid was the main impurity in the nitrogen dioxide gas mixtures generated by
the BIPM NO2 facility and this was corrected by quantifying the mole fraction of nitric
acid directly using FT-IR spectroscopy with traceability to line parameters within the
HITRAN database. The determination of nitric acid was assessed using a (48 ±1.2) m
multipath gas cell in the FTIT system.
A5. Complementary information on the cylinder
Please report the value of the pressure left in the cylinder before shipment to the
BIPM:
If any other component other than NO2, nitrogen and oxygen was detected and/or
quantified please report its mole fraction in the table below:
10
Component
Mole fraction /
nmol/mol
Expanded uncertainty
nmol/mol
Coverage factor
Measurement
technique
HNO3
141
85
2
FT-IR Spectroscopy
The choice of the procedure used for gas analysis is the responsibility of the participating laboratory.
Nevertheless, for a proper evaluation of the data, it is necessary that the calibration method, as well as
the way in which the calibration mixtures have been prepared is reported to the co-ordinators.
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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Bibliography
(1)
(2)
(3)
Flores E., Moussay P., Viallon J., Wielgosz R., Fernández T., Ramírez S., Rojo A., Shinji U.,
Waldén J., Sega M., Sang-Hyub H., Macé T., Couret C., Qiao H., Smeulders D., Guenther F., J
Thorn W., Tshilongo J., Godwill Ntsasa N., Štovcík V., Valková M., Konopelko L., Gromova
E., Nieuwenkamp G., Wessel R., Milton M., Harling A., Vargha G., Tuma D., Kohl A. and
Schulz G.: Final report on international comparison CCQM-K74: Nitrogen dioxide, 10
µmol/mol Metrologia, 49, Tech. Suppl., 08005 (2012 ).
AIJaZM C. Probert: An intercomparison of low flow gas facilities at eleven European
laboratories using a Molbloc transfer package: EURAMET.MM.FF-S3 (EURAMET Project no
806) Metrologia 45, Tec. Sup. (2008).
DWT Griffith: Synthetic calibration and quantitative analysis of gas phase FTIR spectra.
Applied spectroscopy 50 (1996) 59-70
A comparison of nitrogen dioxide (NO2) in nitrogen standards at 10 μmol/mol by Fourier Transform Infrared Spectroscopy (FT-IR)
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