9/5/2010
Online measurement of gaseous I2 and
activated iodine compounds after
selective uptake in lab-generated aerosols
using time-of-flight aerosol mass spectrometry
Kundel, Michael; Ries, Marco; Bosle, Janine; Müller, Ute; Huang, Ru-Jin; Schott,
Mathias
and Hoffmann, Thorsten
International Aerosol Conference 2010, Helsinki, 03.09.2010
Environmental impact of molecular iodine in the
marine boundary layer
Clouds
• ozone depletion
• new particle formation
• affects radiative forcing
I
New aerosol
particles
Iodine oxide
polymers
-
-
IO3
1
9/5/2010
Present analytical methods
Limit of detection (I2)
time resolution
Spatiality
Denuder (GC-MS) 0.17 ppt (500 mL / min)
30 min
single-point
DOAS
30 min
several km
~ 20 ppt
Long-Path DOAS
Mace Head Atmospheric Research Station
(53o20’ N, 9o54’ W)
• What is needed – single point on-line method
Schematic diagram of the Aerodyne ToF-AMS
MCP detector
ion reflector
electronics
hardmirror
chemical analysis
ToF-MS
orthogonal
extractor
aerodynamic lens
quadrupol
aerosol
aerosol vaporizer
filament
critical orifice
chopper
TP: turbo molecular pump
ToF-AMS
particle ToF measurement
ng/m3
NO3-
3
SO42-
3
→ direct measurement of gaseous I2 by ToF-AMS is not possible
NH4+
30
Cl-
20
→ I2 has to be transferred from the gas phase to the particle
phase
Org
25
~ 1 ppt
→ high sensitivity to measure particulate NO3-, SO42-, NH4+, Cland organics
2
9/5/2010
Experimental setup:
Selective uptake of I2 into α-cyclodextrin / NH4Br
rotameter
water
0.75 L/min N2
thermostat
25
°C
diffusion capillary
N2 + I2
solid I2
vial
dryer
AMS
1.1 L/min
Aerosol generator
(pneumatic atomizer)
N2
overflow
aqueous / alcoholic
α-cyclodextrin / NH4Br
solution
α-cyclodextrin
molecular iodine
water
Data analysis
Mass spectra and peak integration
7
intensity / a.u.
6
• mass spectrum of the lab-generated
lab generated aerosol
60 mg α-CD + 6 mg NH4Br
in 990 ml MeOH / 10 ml H2O
5
4
3
2
1
0
50
100
150
m/z
7
200
250
intensity / a.u.
6
5
4
m/z 254
3
2
• mass spectrum of the lab-generated aerosol
after addition of 124 ppb I2
1
0
50
100
-3
1.6x10
1.4
150
m/z
200
I2+
msdiff
fit msdiff
1.2
intensity / a.u.
250
1.0
0.8
org. signal
0.6
• peak integration at m/z 254
→ m/z 253.8: I2
→ m/z 254.05: org. signal
0.4
0.2
0.0
253.6
253.8
254.0
m/z
254.2
254.4
3
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Influence of NH4Br on the I2 signal
ratio m/z 253.8 / m/z 69
4x10
-3
3
2
1
0
0.0
0.2
0.4
0.6
0.8
molar ratio NH4Br / α-CD
1.0
1.2
• addition of NH4Br to α-CD-solution, mixing ratio I2= 8 ppb
→ increasing signal intensity at m/z 253.8 due to the formation of I2 + Br- → I2Br→ maximum at molar ratio of ~ 1.0
Time resolved mass traces for the on-line
measurement of molecular iodine
2.5
intensity / a.u.
2.0
• m/z 69.0 and m/z 60.0 are markers for α-CD,
m/z 78.9 is a marker for Br→ output of lab-generated aerosol is stable
m/z 69.0: org
m/z 60.0: org
m/z 78.9: 79Br-
1.5
1.0
0.5
0.0
0.0
0.2
0.4
0.6
time / hours
-3
1.2x10
0.8
1.0
• opening the I2 test gas source
→ signal at m/z 253.8 (I2+) increases immediately
inttensity m/z 253.8 / a.u.
1.0
0.8
addition of
1.0 ppb I2
0.6
0.4
0.2
• closing
g the I2 test g
gas source
→ signal at m/z 253.8 (I2+) decreases
0.0
0.0
ratio m/z 253.8 / m/z 69 / a.u.
5x10
0.2
0.4
0.6
time / hours
0.8
1.0
-4
4
3
• variation of the absolute signal can be reduced
using the ratio between m/z 253.8 and m/z 69.0
addition of
1.0 ppb I2
2
1
0
0.0
0.2
0.4
0.6
time / hours
0.8
1.0
4
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Analytical performance
I2
I (253.8 / 69)
ppb
a.u.
0,00
0,00007
0,70
0,00020
2,48
0,00092
5,03
0,00226
8,09
0,00374
12,71
0,00487
23,33
0,00757
46,90
0,02172
90,53
0,04200
124,01
0,05620
-3
3
R2=0.997
50
40
30
20
10
LOD = yB + 3sB
LOQ = yB + 10sB
0
0
20
40
60
80
mixing ratio I2 / ppb
100
120
LOD
LOQ
I2
ppt
100
331
• a dilution chamber was used to obtain various I2 mixing ratios in the ppb- and ppt-range
Comparison ToF-AMS vs Denuder GC-MS
I2 / ppb (ToF-AMS)
ra
atio m/z 253.8 / m/z 69 / a.u.
60x10
RSD
%
21,2
25,7
13,8
10,2
7,3
6,9
16,5
16,8
2,9
1,9
60
40
20
0
0
20
40
I2 / ppb (Denuder GC-MS)
ToF-AMS
I2 / ppb
0,45
3,25
72,25
RSD / %
7,2
2,1
0,8
Denuder
GC-MS
I2 / ppb
0,48
3,08
67,67
RSD / %
10,5
1,2
3,5
60
5
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Proof of principle:
Time resolved emission of I2 from seaweed
O3 analyzer
overpressure
Organoiodine
compounds
TD-GC-MS
3 L flow reactor
synth. air
+ O3
4.5 L / min
→ residence time
~ 40s
I2
ToF-AMS
I2
denuder sampling
followed by GC-MS
Time resolved emission of I2 from freeze dried
Laminaria digitata
-1
em
mission of I2 ng min gFW
W
-1
60
50
40
30
addition of
Laminaria digitata
~ 20 ppb O3
20
10
increasing O3 to 100 ppb
0
0.0
0.5
O3
ppb
20
1.0
1.5
time / hours
2.0
2.5
I2 Max
I2
I2
ng min-1 gDW-1 ng h-1 gDW-1 ng min-1 DW-1
57,82
2248,56
37,48
6
9/5/2010
Time resolved I2 emissions from living
Laminaria saccharina
0.30
-1
emission of I2 ng min gFW
W
-1
100 ppb O3
50 pp
ppb O3
0.25
0.20
0.15
0.10
addition of
Laminaria saccharina
0.05
0.00
0.0
O3
ppb
100
50
~3
0.1
0.2
0.3
0.4
time / hours
0.5
0.6
I2 max
I2
I2
I2
ng min-1gFW-1 ng h-1 gFW -1 ng min-1 gFW -1 pmol min-1 gFW -1
this study
0,27
9,43
0,16
0,62
this study
0,21
8,48
0,14
0,56
0,55
Ball et al., 2009 (BBCEAS)
Conclusions and outlook
• selective uptake of gaseous I2 in lab-generated
lab generated α
α-cyclodextrin
cyclodextrin / NH4Br
Br-particles
particles inside a 0
0.5
5 L flow
tube enables the measurement of gaseous I2 by ToF-AMS with a time resolution of 3 min
→ LOD= 100 ppt, LOQ= 331 ppt
(could still be improved by instrumental modifications by a factor 5-10)
• time resolved emission of I2 from freeze dried Laminaria digitata and living Laminaria saccharina
was investigated
→ time resolved I2 emission from different seaweed plants will be studied as well as the influence of
ozone on the I2 emission
• measurement of activated iodine compounds (e.g., ICl) after selective uptake in lab-generated
1,3,5-trihydroxybenzene particles
OH
OH
→ LOD= 800 ppt, LOQ= 2,6 ppb
+
HO
OH
I
+
Cl
HO
H Cl
OH
I
7
9/5/2010
Acknowledgement
• Prof. Dr. Thorsten Hoffmann
• Work group Hoffmann
• Marine Integrated Algal Aquaculture Sylt
• supported by the German Research Foundation (DFG)
within the Research Training Group 826:
Trace Analysis of Elemental Species:
Development of Methods and Applications
Thank you for your attention !
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