S in ambient air by gc pid fpd acs fall 2013 final

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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


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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


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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


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FPD Schematic


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Photo of PID Analyzers GC 301 C


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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


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


Chromatograms of PID & FPD overlapped

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Extended Range of PID


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


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


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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


Technology

S in ambient air by gc pid fpd acs fall 2013 final