International Supplementary comparison
COOMET.QM-S2 (COOMET project № 556/RU/12)
COMPARISON OF PRIMARY STANDARD GAS MIXTURES:
GRAVIMETRY PRODUCTION OF CH4 IN SYNTHETIC AIR (100 μmol/mol)
Saint-Petersburg
2013
Final report
L.A. Konopelko1, Y.A. Kustikov1, A.V. Kolobova1, V.V. Pankratov1, M. Bednova1,
O.V. Efremova1, Andreia de Lima Fioravante2, Claudia Cipriano Ribeiro2, Cristiane
Rodrigues Augusto2, Denise Cristine Gonçalves Sobrinho Teixeira2, Elizandra Cananea de
Sá Elias2, Rutger Jacob Oudwater2, Suellen Cristina Sales Pereira de Sousa2
1
D.I. Mendeleyev Institute for Metrology (VNIIM), 19 Moskovsky Prospekt, 190005, St-
Petersburg, Russia;
2
Instituto Nacional de Metrologia (Inmetro), Qualidade e Tecnologia Av. Nossa Senhora
das Graças, 50 - Xerém - cep: 25.250-020, Prédio 4 - Duque de Caxias - RJ - Brasil
Field
Amount of substance: Gas analysis
Subject
Supplementary comparison of primary standard gas mixtures - Methane in Synthetic Air
(100 μmol/mol)
Participants
VNIIM (Russia), Inmetro (Brazil)
Organizing body
TC 1.8 «Physical Chemistry» COOMET
2
1. Background
Methane is one of the main components of greenhouse gases in the atmosphere. Its
confident measurement is an important issue in monitoring changes in the global
environment, as this gas is presumed to contribute to climate change. Methane in air at
ambient level is the subject of CCQM comparison CCQM-K82 (2012-2013).
The objective of present preparative comparison is demonstration of each NMI’s capability
in GRAVIMETRIC PRODUCTION OF PRIMARY STANDARD GAS MIXTURE (PSM) OF
METHANE IN SYNTHETIC AIR in the concentration range 10 to 1000 µmol/mol. The
nominal amount-of-substance fraction level for methane is 100 µmol/mol with synthetic air
matrix.
This comparison was proposed in 2011 within the cooperation program in the field of
metrology between VNIIM and INMETRO. In 2012 it was registered as COOMET regional
comparison.
2 Conduct of the Comparison
The participants prepared gas mixtures for the comparison gravimetrically in accordance
with requirements of ISO 6142 [1] and studied regarding their composition and stability in
accordance with requirements of ISO 6143 [2].
All the PSMs were prepared in cylinders of 5 dm 3 nominal and with pressure
approximately 10,0 MPa.
Inmetro prepared 1 PSM of methane in synthetic air on the level of 100 µmol/mol, carried
out verification measurements against 3 calibration standards, produced by VSL, with
certified values in the range 30 to 150 µmol/mol. After verification and stability testing the
prepared PSM was sent to VNIIM for measurements.
VNIIM prepared 3 PSMs of methane in synthetic air on the level of 100 µmol/mol, carried
out verification measurements. Then the Inmetro PSM was measured with reference to 3
VNIIM PSMs.
3 Measurement protocol
The measurement protocol requested each laboratory to perform at least 3 measurements
obtained under repeatability conditions including at least three separate calibrations. The
protocol informed the participants about the nominal concentration of methane. The
laboratories were also requested to submit a summary of uncertainty evaluation for the
presented results.
3
4 Measurement methods. calibration and verification procedures
Summary of measurement and calibration (verification) methods is shown in table 1.
Table 1 Measurement and calibration methods
Laboratory
Measurement
Calibration and
method
verification
method
Inmetro
GC-FID
Calibration curve
3 VSL standards
VNIIM
NDIR
One point calibration
3 own standards
Total number of
measurements
1 measurement
10 submeasurements
3 measurements
5 sub-measurements
VNIIM prepared 3 primary gas mixtures (СH4/synt air). All of them had nominally similar
methane mole fraction on the level of 100 µmol/mol. Verification (NDIR) was carried out by
establishing consistency between these nominally similar mixtures and also with similar
mixture prepared previously. Measurements (NDIR) of INMETRO gas mixture were
carried out on the same instrument against the 3 mixtures. The sequence was VNIIM
cyl.1→ INMETRO cyl.→ VNIIM cyl.1→ VNIIM cyl.2→ VNIIM cyl.1.→ VNIIM cyl.3→ VNIIM
cyl.1→INMETRO cyl.→ VNIIM cyl.1→…….
5 Results
The results of measurement of the methane mole fraction in the Inmetro PSM (cylinder N
D9340057) are shown in table 2
Table 2
Inmetro
ux1,assign = 0,85
µmol/mol
x1grav
µmol/mol
99.75
Ux1,assign,
ux1,grav
ux1,ver
ux1,stab
µmol/mol,
k=2
0.024
0.77
0.35
1.70
x1pred
µmol/mol
99.60
VNIIM
u x1,pred = 0,10
µmol/mol
Ux1,pred,
ux2,grav
umeas.
µmol/mol,
k=2
0.023
0.10
0.20
where
x1,grav - amount of substance fraction of Inmetro PSM from gravimetry;
ux1,grav - standard uncertainty of gravimetrical preparation and purity;
ux1,ver - standard uncertainty from verification;
ux1,stab - standard uncertainty of stability;
ux1,assign - assigned combined standard uncertainty of Inmetro PSM ;
Ux1,assign - assigned expanded uncertainty of Inmetro PSM, k=2;
4
x1,pred - amount of substance fraction of Inmetro PSM predicted from VNIIM
measurements;
ux2,grav - standard uncertainty of gravimetrical preparation and purity (for VNIIM PSMs);
umeas. - standard uncertainty of measurements (umeas. was calculated as combination of
repeatability and reproducibility standard deviation. Repeatability standard deviation was
on the level of 0,05 %);
ux1,pred -combined standard uncertainty of predicted amount of substance fraction from
VNIIM measurements of Inmetro PSM, ux1,pred = √u2x2 , grav +u2meas ;
Ux1,pred - expanded uncertainty of predicted amount of substance fraction from VNIIM
measurements of Inmetro PSM, k=2.
6 Degree of equivalence
The pair-wise degree of equivalence D in this comparison is defined in accordance with
the equation:
D=∣x1 pred −x1 grav∣
The standard uncertainty of the pair-wise degree of equivalence can be expressed as:
u( D)=√ u2x1,pred +u2x1,grav
The expanded uncertainty U ( D) at a 95 % confidence level
U ( D)=k √ u2x1,pred +u2x1,grav
where k is a coverage factor, k=2
Note - This bilateral comparison was planned as preparative. The procedure of the
comparison corresponded to scheme for other CCQM preparative comparisons and was
as follows: INMETRO sent its gravimetrical gas mixture to VNIIM, VNIIM carried out
measurements against its primary standards and compared INMETRO gravimetrical value
with the measured by VNIIM.
The difference here is that in the preparative comparison the reference value is calculated
on the basis of regression of results (gravimetric data and analytical signals) of all the
participants and for bilateral study we have only two result points with only one straight
line, which should cross these points and experimental data and KCRV would be the
same. So we could not use the traditional approach for calculation of KCRV.
On the other hand in calculating of uncertainty of pair-wise degree of equivalence we took
into consideration only INMETRO and VNIIM gravimetric uncertainties and VNIIM
5
measurement uncertainty, and did not include components due to verification as it usually
done in analytical comparisons.
7 Summary results
Table 3
Lab
Cylinder
INMETRO
VNIIM
D9340057
D249398
xi,grav
uxi,grav
umeas
xi,pred
uxi,pred
D
µmol/mol
µmol/mol
µmol/mol
µmol/mol
µmol/m
ol
µmol/mol
99.75
100.24
0.024
0.023
0.10
99.60
-
0.103
-
0.15
k
U(D)
µmol/mol
2
0.21
8 Conclusions
Inmetro and VNIIM PSMs for methane in synthetic air (100 μmol/mol) are in a good
agreement – the pair-wise degree of equivalence is substantially smaller than its
expanded uncertainty.
References
[1] International Organization for Standardization, ISO 6142:2001 Gas analysis Preparation of calibration gas mixtures - Gravimetric methods, 2nd edition.
[2] International Organization for Standardization, ISO 6143:2001 Gas analysis –
Comparison methods for determining and checking the composition of calibration gas
mixtures.
Coordinator
Leonid Konopelko
VNIIM, Research Department for the State Standard in the Field of Physical-Chemical
Measurements (PCD),
19, Moskovsky pr., St.-Petersburg, 198005, Russia
Phone: +7 812 3151145
E-mail: [email protected]
Completion Date
October 2013
6
Annex A
Reports submitted by participating laboratories
INMETRO Report
1 INFORMATION ABOUT PARTICIPATING INSTITUTE:
Inmetro – Instituto Nacional de Metrologia, Qualidade e Tecnologia
Institute
Address
Contact Person
NMI Participants
Telephone
Av. Nossa Senhora das Graças, 50 - Xerém - cep: 25.250-020
Prédio 4 - Duque de Caxias - RJ - Brasil
Cristiane Rodrigues Augusto
Andreia de Lima Fioravante, Claudia Cipriano Ribeiro, Cristiane
Rodrigues Augusto, Denise Cristine Gonçalves Sobrinho Teixeira,
Elizandra Cananea de Sá Elias, Rutger Jacob Oudwater, Suellen
Cristina Sales Pereira de Sousa
(++55) (21) 2679-9243
(++55) (21) 2679-9069
Fax
[email protected]
email
2 CYLINDER DETAILS
Date of mixture preparation
03/02/2012
Volume (L)
5
Total Pressure (bar)
100
Connection type (e.g. DIN1, BS14 etc.)
DIN1
3.1 PURITY TABLE FOR NOMINALLY PURE CH4 (OR CH4 PARENT MIXTURE)
Complete for all components considered:
Component
Method*
Mole Fraction
(µmol/mol)
Standard uncertainty
(µmol/mol)
CH4
GC-FID
499.9255984584
0.1174747626
N2
ISO 6142 purity estimation
from supplier info
999499.471951887
9
0.2259388744
C3 H8
ISO 6142 purity estimation
from supplier info
0.0002499647
0.0001443170
CO
ISO 6142 purity estimation
from supplier info
0.0502249682
0.0272420697
CO2
ISO 6142 purity estimation
from supplier info
0.0007498940
0.0004329498
C2 H6
ISO 6142 purity estimation
from supplier info
0.0004999293
0.0002886338
H2O
ISO 6142 purity estimation
from supplier info
0.2501249823
0.1315116737
O2
ISO 6142 purity estimation
from supplier info
0.2501249824
0.1315116737
THC
ISO 6142 purity estimation
from supplier info
0.0499750036
0.0272416874
C2 H4
ISO 6142 purity estimation
from supplier info
C3 H6
ISO 6142 purity estimation
from supplier info
0.0002499647
0.0002499647
0.0001443171
0.0001443170
3.2 PURITY TABLE FOR NOMINALLY PURE N2
Complete for all components considered:
Component
Method*
Mole Fraction
(mol/mol)
Standard uncertainty
(mol/mol)
N2
ISO 6142 purity estimation
from supplier info
0.999999400
0.000000200
CO
ISO 6142 purity estimation
from supplier info
0.000000050
0.000000290
H2O
ISO 6142 purity estimation
from supplier info
0.000000250
0.000000140
O2
ISO 6142 purity estimation
from supplier info
0.000000250
0.000000140
CxHy
ISO 6142 purity estimation
from supplier info
0.000000050
0.000000029
3.3 PURITY TABLE FOR NOMINALLY PURE O2
Complete for all components considered:
Component
Method*
Mole Fraction
(mol/mol)
Standard uncertainty
(mol/mol)
O2
ISO 6142 purity estimation
from supplier info
0.999999125
0.000000238
N2
ISO 6142 purity estimation
from supplier info
0.000000275
0.000000158
Ar
ISO 6142 purity estimation
from supplier info
0.000000150
0.000000086
CO
ISO 6142 purity estimation
from supplier info
0.000000050
0.000000028
CO2
ISO 6142 purity estimation
from supplier info
0.000000050
0.000000028
H2
ISO 6142 purity estimation
from supplier info
0.000000050
0.000000028
H2O
ISO 6142 purity estimation
from supplier info
0.000000250
0.00000014
CxHy
ISO 6142 purity estimation
from supplier info
0.000000050
0.000000028
9
4. PURITY TABLE FOR FINAL CH4/synth. air MIXTURE
Complete for all components considered:
Component
Mole Fraction
(µmol/mol)
Standard uncertainty
(µmol/mol)
CH4
99.7546444933
0.0238817000
N2
790680.1095610410
8.9455560500
C3 H8
0.0000498777
0.0000288000
Ar
0.0313829578
0.0181189600
CO
0.0500448899
0.0189739600
CO2
0.0106106190
0.0060402700
C2 H6
0.0000997554
0.0000575900
H2
0.0104609859
0.0060396500
H2O
0.2500249388
0.0919350900
O2
209219.7330256730
8.9450998500
THC
0.0499950123
0.0189739400
C2 H4
0.0000498777
0.0000288000
C3 H6
0.0000498777
0.0000288000
5. VERIFICATION
The prepared reference gas mixture was measured against VSL’s PRMs. The reference values for
the amount-of-substance fractions are obtained by interpolation using a calibration curve. The
following results are presenting the uncertainty as standard deviation of the measurements, with 10
(ten) repetitions in one single day. The results from the GC-FID measurements have been fitted using
a linear function, in accordance with ISO 6143, using the software b-least.
Table A1 – Calibration mixtures for Methane in air
Mixture
x
µ mol mol-1
u(x)
µ mol mol-1
y
(area)
PRM D247556*
PRM 8541*
PRM M60296*
29.99
100.0
150.10
0.15
0.35
0.35
546.55
1851.93
2790.27
u(y)
(standard
deviation)
1.39
4.61
33.58
*Prepared by Dutch Metrology Institute (VSL).
What CH4 mole fraction was predicted from
your verification analysis?
xCH4,anal: 99.7830
What is your estimate of the uncertainty
(standard) in xCH4,anal ?
u(xCH4,anal) : 0.7736
10
6. STABILITY TESTING
The stability of the PSM is ensured by a previous study carried out for a period of one year.
To calculate the PSM final uncertainty was used the uncertainty of the stability study from a
PSM with the same concentration of the PSM prepared for this comparison (100 µmol/mol).
7. FINAL RESULTS
The results are presented in following table with data:
xprep
uprep
uver
ust
ucert
U(k=2)
amount of substance fraction , from preparation (mmol.mol-1)
uncertainty of xprep from gravimetrical preparation and purity (mmol.mol-1)
uncertainty from verification (mmol.mol-1)
uncertainty of stability (mmol.mol-1)
final uncertainty of x (mmol.mol-1)
stated uncertainty of x, at 95% level of confidence (mmol.mol-1)
Standard uncertainty of the mixture was calculated with following formula:
ucert =√ u2prep +u2ver +u 2st
Componen
t
xprep
mmol
mol-1
uprep
mmol
mol-1
uver
mmol
mol-1
ust
mmol
mol-1
ucert
mmol
mol-1
Methane
99.7546
0.0238
0.7736
0.3545
0.8513
X
mmol mol-1
U(k=2)
mmol mol-1
99.75
1.70
11
VNIIM Report
1 INFORMATION ABOUT PARTICIPATING INSTITUTE:
Institute
Address
Contact Person
Telephone
Fax
email
VNIIM
D.I. Mendeleyev Institute for Metrology
19, Moskovsky pr., St. Petersburg, 198005, Russia
Leonid Konopelko
+7 (812) 315-11-45
+7 (812) 327-97-76
[email protected]
2 CYLINDER DETAILS
Date of mixture preparation
22.06.2012
Volume (L)
5
Total Pressure (bar)
100
Connection type (e.g. DIN1, BS14 etc.)
Rotarex
3.1 PURITY TABLE FOR NOMINALLY PURE CH4
CYLINDER N 62449
Component
Method
Mole Fraction
(µmol/mol)
Standard uncertainty
(µmol/mol)
Н2O
Hygrometry,
condensation method
5
0.5
CO2
GC-TCD (micro),
FID+methanator
1.0
0.6
C2H4
1.0
0.6
C2H6
C3H6
C3H8
1-C4H8
изо-C4H8
1,3-C4H8
N2
GC-FID
GC-FID
GC-FID
GC-FID
GC-FID
GC-FID
GC-FID
GC-TCD
0.50
0.50
0.50
0.50
0.50
0.50
4.5
0.29
0.29
0.29
0.29
0.29
0.29
0.6
O2+Ar
GC-TCD
0.84
0.16
-
999984.7
1.5
CH4
12
3.2 PURITY TABLE FOR NOMINALLY PURE N2
CYLINDER N 22558
Component
Method*
Mole Fraction
(µmol/mol)
Standard uncertainty
(µmol/mol)
H2O
Hygrometry,
condensation method
1.50
0.07
CO2
GC-PDHID,
GC-FID+methanator
1.484
0.010
CO
GC-FID+methanator
0.2130
0.0023
O2
Coulometric analyser
0.0201
0.0012
CH4
GC-FID
0.015
0.009
N2
-
999996.77
0.07
3.3 PURITY TABLE FOR NOMINALLY PURE O2
CYLINDER N 910287
Component
Method*
Mole Fraction
(µmol/mol)
Standard uncertainty
(µmol/mol)
CO2
GC-PDHID
0.0768
0.0037
CO
GC-PDHID
0.0075
0.0044
CH4
GC-PDHID
0.0338
0.0009
O2
-
999999.882
0.006
3.4 PURITY TABLE FOR NOMINALLY PURE Ar
CYLINDER N 205863
Component
Method*
Mole Fraction
(µmol/mol)
Standard uncertainty
(µmol/mol)
O2
Coulometric analyser
0.174
0.004
N2
GC-AID
0.170
0.023
CH4
GC-FID
0.095
0.0014
CO2
GC-FID+methanator
0.030
0.017
H2
GC-AID
0.025
0.014
CO
GC-FID+methanator
0.010
0.006
Ar
-
999999,50
0,03
13
3.5 PURITY TABLE FOR NOMINALLY PURE CO2
CYLINDER N 226934
Component
Method*
Mole Fraction
(µmol/mol)
Standard uncertainty
(µmol/mol)
H2O
Hygrometry,
condensation method
15
0.7
N2
GC-TCD
1.06
0.07
CH4
GC-TCD
0.5
0.3
CO
GC-TCD
0.5
0.3
H2
GC-TCD
0.5
0.3
O2
GC-TCD
0.25
0.13
CO2
-
999982.2
0.9
4. PURITY TABLE FOR FINAL CH4/synth. air MIXTURE
Complete for all components considered:
Component
Mole Fraction
(µmol/mol)
Standard uncertainty
(µmol/mol)
Expanded
uncertainty, k=2
(µmol/mol)
CH4
100,24
0,023
0,046
CO2
378,76
Ar
9286
0,09
3,3
0,18
7
O2
209189
7,3
15
N2
balance
-
-
Notes:
1 There were prepared 3 similar PSMs with slightly different methane concentrations – 100,24; 100,04
and 100,09 µmol/mol by 3 step dilution (5,5 %, 0,2 %, 100 µmol/mol) from the same pure gases.
2 Standard uncertainty for PSMs is calculated only on the base of gravimetrical preparation – verification
and stability components are not included.
14
5. VERIFICATION
Briefly describe your verification procedure. For example was it by comparison with other
traceable CH4/synth. air standards; how many such standards; which analytical methods
were used?
Verification was carried out by checking consistency between three nominally similar
prepared mixtures and also by comparison with older VNIIM measurement standard.
Analytical method - NDIR
What CH4 mole fraction was predicted from
xCH4,anal: 100,15 µmol/mol
your verification analysis?
What is your estimate of the uncertainty
(standard) in xCH4,anal ?
u(xCH4,anal) :0,1 µmol/mol
6. STABILITY TESTING
Briefly describe any measures undertaken to confirm the stability of the mixtures in the period
between their preparation and their shipping to the coordinator
The stability of the PSM is ensured by previous investigations.
15