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WP1 and WP2 highlights
Stefan Persijn
KEY-VOCs Webinar 5 September 2017
www.key-vocs.eu
WP1 Adsorption and reaction effects on surface materials and zero gas standards
WP2 Reference standards to underpin atmospheric monitoring of VOCs
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Why study the surface interaction?
Make sure that your
measurements are correct
Reduce the use of your
valuable reference gas
mixtures
Speed up the
measurements
3
Obtain accurate gas
standards for calibration of
your analyser
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Approaches followed to investigate VOC adsorption
Adsorption in tubings Experimental and modeling studies of adsorption-desorption kinetics of
OVOCs in sampling lines
Surface analysis Characterize chemical speciation on surfaces via x-rays
Adsorption in cylinders Decanting studies of OVOC gas mixtures and comparison with
dynamically prepared gas mixtures
4
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Set-up for quantifying the adsorption in tubings
Step 1
Methanol mixture via bypass to CRDS
Test tube flushed with N2
Step 2
Methanol mixture via test tube to CRDS
Methanol : 182 nmol/mol
Flow : 0.55 L/min
Temperature : 20 °C
Test tube
5
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Set-up for quantifying the adsorption in tubings
Step 1
Methanol mixture via bypass to CRDS
Test tube flushed with N2
Step 2
Methanol mixture via test tube to CRDS
Methanol : 182 nmol/mol
Flow : 0.55 L/min
Temperature : 20 °C
Test tube
6
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Adsorption in SS304 with(out) coating
LID = 15.25 m5.3 mm
Inner volume = 0.34 L
Transit time ~ 37 seconds
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Polymers: lowest
Coated metals: intermediate
Uncoated metals: highest
Results adsorption measurements in tubings
Aluminum Copper
PTFE PVDF
SS304
Sulfinert
Silconert
2000
Methanol
amount
fraction:
182 nmol/mol
Material
Molecules
adsorbed
(x1011 cm-2)
Corrected for
gas exchange
PTFE 1.44±0.09
PVDF 1.8±0.1
Silconert 2000
coated SS304 3.2±0.1
Sulfinert
coated SS 50 ±2
SS304 (2.6±1.6)·102
Aluminium (3.8±1.8)·102
Copper (6.4±2.8)·103
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Methanol adsorption (3 ppm) in tubings at elevated temperatures using FID
Material Type Treatment 50 °C 100 °C
Stainless
steel
321 none =
strong adsorption
=
no methanol detectable
316 Electro-
polished =
strong adsorption
=
moderate/strong adsorption
316 Sulfinert®
coating
< <
304 < <
Polymer
PFA
none
< =
high outgassing
PEEK some adsorption some outgassing/adsorption
<
<
Test tubing inside GC oven
9
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4,7
4,8
4,9
5,0
5,1
5,2
5,3
5,4
5,5
5,6
5,7
Cy
lin
der
1
Cy
lin
der
2
Cy
lin
der
3
Mea
n v
alu
e
Cylinders
Acetone 1.0 %
Homogeneity of OVOC mixtures at 100 ppb
2,9
3,0
3,1
3,2
3,3
3,4
3,5
3,6
3,7
3,8
3,9
Cy
lin
der
1
Cy
lin
der
2
Cy
lin
der
3
Mea
n v
alu
eCylinders
Ethanol
3.5 %
0,9
1,0
1,1
1,2
1,3
1,4
1,5
1,6
1,7
1,8
1,9
Cy
lin
der
1
Cy
lin
der
2
Cy
lin
der
3
Mea
n v
alu
e
Cylinders
Methanol
4.7 %
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Formaldehyde: decanting and pressure effect
\
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Decanting losses cylinders
Cylinder type
A B C D * Other (SW)
Formaldehyde (○) + ○ +
Methanol ▬ ○ ▬ ▬ ○
Ethanol ○ + ▬ ▬ (+)
Acetone + + (○) (+) +
Methacrolein + + + + +
MVK + + + + +
MEK + + ○ ○ +
* Formaldehyde cylinders differ from OVOC cylinders
+ (D < 5 %) ○ (D 5…10 %) ▬ (D >10 %)
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1 year stability performance of short-lived species (100 nmol/mol) in different cylinders types with sampled enriched-GC-FID
14
+5%
- 5%
Analytical uncertainty 2 % Analytical uncertainty 5 %
+5%
- 5%
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Towards analysis of surface adsorption: ethanol on SS
▬ EtOH in gas phase measured in
transmission mode (for comparison)
▬ surface signal with EtOH in gas cell
▬ surface signal without EtOH in gas cell
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ReGaS2 : Mobile Gas Generator
Uncertainty budget
MVK 23 ppb ± 3.1%
MVK generation & measurement with ATD-GC-FID Dynamic generation with permeation
VOCs at ppb level
1-5 compounds simultaneously
Stability of RGM ≤ 0.4 %
Reproducibility of RGM ≤ 0.7 %
SilcoNert2000® coating
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VOC-free zero gas: removal dependent on type of purifiers
17
VOC-free zero gas important for dilution and zero point calibration. Types: inorganic media and metal catalysts VOCs: NMHCs, monoterpenes, OVOCs
More info in the 5 min presentation of Jennifer Englert (DWD)
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Conclusions
Gas standards for atmospheric monitoring
Cylinder treatment plays a crucial role in the accuracy and stability
ldentified cylinder types with best performance (in general coated SS)
Methanol, acethaldehyde and formaldehyde do not meet the DQOs for
uncertainty and stability
Zero gases Removal of impurities is purifier dependent
Extending the certification protocol zero gas to VOCs
18
Adsorption in tubings Polymer tubings best (when not heated) but subject to permeation.
Coated tubings good alternative & preferred for applications where
heating is required.
Portable generators Portable generators produce reference gas mixtures of reactive
compounds at atmospheric level to calibrate instruments in the field