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S Compounds by Hyphenated GC/PID- FPD
John N. Driscoll & Jennifer Maclachlan PID Analyzers, LLC
Sandwich. MA 02563Presented at the ACS Fall Nat. Meeting
Indianapolis, IN Sept. 2013
PID Analyzers, LLC url: http://www.hnu.com
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Introduction• The S compounds of interest in the
atmosphere include H2S, DMS, COS, SO2,and CS2.
• We were interested in determining the detection limits, reproducibility, linearity of the Flame Photometric Detector (FPD) for S compounds
• We wanted to use a photoionization detector (PID) with an FPD in series to improve the response and detection limits
PID Analyzers, LLC url: http://www.hnu.com
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Methods for S Cpds
• EPA- Gas Chromatography/Flame Photometric Detector
• For stack (with a dilution system) or ambient air analysis
• EPA DL- app. 100 ppb• BA APCD DL- 500 ppb
PID Analyzers, LLC url: http://www.hnu.com
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Using the PID In combination with a S Selective Detector (FPD)
• PID/FPD- The PID is nearly 100x more sensitive for H2S and CH3SH, than the FPD, the dynamic range is > 107 and it provides additional confirmation that no HC are present
• A ratio of the response factor PID/FPD will confirm that only a S compound is present since the PID responds to both S & HC
• Response of the PID is linear with concentration while the FPD (S) is sq rt. with concentration PID Analyzers, LLC url: http://www.hnu.com
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FPD & PID for Sulfur Compounds
2 11
PID Analyzers, LLC url: http://www.hnu.com
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FPD Schematic
PID Analyzers, LLC url: http://www.hnu.com
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Photo of PID Analyzers GC 301 C
PID Analyzers, LLC url: http://www.hnu.com
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Abundance of S Compounds in the Atmosphere + DL FPD & PID
Source S levels: Chemistry of the Natural Atmosphere, Peter Warneck, Academic Press, NY (1988)
S Compoun
d
ppb S in the
Atmosphere
FPD D L ppb
Need Conc.
PID DL ppb
IP (eV)
Dimethyl Sulfide 40-110 100 Y 1 8.43
Sulfur Dioxide 160+/-100 100 Y NR 12.5Hydrogen
Sulfide 121-829 100 N 10 10.46Carbon
Disulfide 37 +/- 10 20 N 2 10.07Carbonyl Sulfide 509+/- 63 50 N NR 11.18
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Lifetime of Sulfur Compounds in the Lower
Atmosphere
Rate Coefficients ( !0-12 cm3/molecule s)
Compound OH Rate* O rate*Lifetime in
Troposphere
Days
H2S 5.0, 5.6 0.027 4.4
CH3SH 90, 130 1.9 0.3
DMS 9.1, 45 63, 48 0.6
DMDS 223 0.1
CS2 0.43, 2.0 5.5 12
COS >0.04 44 yrs
PID Analyzers, LLC url: http://www.hnu.com
Source: Chemistry of the Natural Atmosphere, Peter Warneck, Academic Press, NY (1988)
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Properties of Sulfur Compounds
S Cpd. BP deg C PEL ppmH2S -60 10
COS -50.3
SO2 -10 2
DMS 37.5 10
CS2 46.3 20
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GC/FPD of Reduced S on thick film capillary + packed columns
Packed column chromatography- Anal. Chem.
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Sensitivity PID/FPD
PID Analyzers, LLC url: http://www.hnu.com
Chromatograms of PID & FPD overlapped
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Extended Range of PID
PID Analyzers, LLC url: http://www.hnu.com
The PID extends the range of the FPD and the latter detector confirms the presence of S
Note: Quenching of FPD at higher H2S levels reduces sensitivity
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Comparison of Exponential vs Linear Fit
4 point Calibration linear fit
0 5 10 15 20 25 300
0.2
0.4
0.6
0.8
1
1.2
1.4H2S Calibration Curve for
FPD
Ppm H2S
4 point cal for linearizaton
Exponential Fit Response
PID Analyzers, LLC url: http://www.hnu.com
Improves linearity
0 5 10 15 20 25 300
0.20.40.60.8
11.21.4
f(x) = 0.151379298894313 exp( 0.084524725326705 x )
H2S by FPD
ppm H2S
PH 0
00
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Reproducibility of H2S via GC/PID-FPD
PID ppm FPD ppm 0.872 0.9425 0.923 1.0728 0.911 0.9703 0.999 1.0173 1 0.8951 1.014 0.9642 0.933 1.0634 1.007 0.9541 0.883 1.0864 1.017 1.0325
Ave 0.95 1Std Dev 0.055 0.064
CV % 5.78 6.39
PID Analyzers, LLC url: http://www.hnu.com
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Summary• Lighting an FPD is frequently an issue but our
piezoelectric igniter simplifies this issue• 4 point calibration in SW improves the
linearity of the FPD for S and eliminates the square root response
• The PID extends the range of the FPD and the latter detector confirms the presence of S
• The reproducibility of both detectors at high ppb levels is similar but the 4 point calibration improved the FPD precision
PID Analyzers, LLC url: http://www.hnu.com