Got Sulfur Analytical Methods in the Odor Threshold Range

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Got Sulfur? Analytical Methods in the Odor
Threshold Range

• Andy Rezendes
• Jim Occhialini
• Alpha Analytical Labs, Inc.
• 8 Walkup Drive
• Westboro, MA 01581
• Michael Lannan
• Tech Environmental
• 1601 Trapelo Road
• Waltham, MA 02451

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Overview

• Gas chromatography and methods review
• Stability of sulfides and mercaptans in canisters
  and Tedlar bags
• Comparison of reporting limits
• Example of landfill gas analysis
• Conclusions

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Conventional GC and GC/MS

• Conventional GC detectors
• Chemiluminecense (ASTM D-5504)
• excellent sensitivity
• very selective and costly
• Flame photometric (EPA method 16)
• not as sensitive
• high signal to noise
• poor linearity

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Conventional GC and GC/MS

• Gas chromatography / mass spectrometry (GC/MS)
• Moderate sensitivity compared to other detectors
• Greater QA/QC capabilities by using internal
  standards
• Analytical instrumentation has multiple
  applications

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Conventional GC vs. GC/MS

• Gas chromatography (GC)
• only retention time of compound used for
  identification
• GC/MS (mass spectrometry)
• spectral confirmation of compound in addition to
  retention time

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Sulfides and Mercaptans via TO-15

• Modification of standard TO-15 procedure
• Can detect sulfides as low as 0.5 ppbV
• Mercaptans and H2S as low as 5.0 ppbV
• Fused silica lined (FSL) sample pathway

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Modified TO-15 Procedure
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Stability Study Summary

• Examines holding times of Sulfides and Mercaptans
  in canisters and bags
• Phase 1A Stability of short list was examined
  in cans
• Phase 1B Stability of additional
  sulfides/mercaptans in cans
• Phase 2 Effect of deactivation process on H2S
  stability
• Phase 3 Tedlar bag stability examined
• Phase 4 Method detection limit study performed

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Fused Silica Lined vs. SUMMA Canisters

• SUMMA refers to the electropolishing technique
  used to deactivate the interior of the canisters
• Fused silica lining (FSL) is a glass coating,
  a.k.a. Silcosteel and Silonite
• FSL more inert and more stable for storage of
• VOCs
• Manufacturer claims holding time up to 7 days for
  sulfides and mercaptans

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Stability Study Summary

• Spike concentrations 5 ppbV and 25 ppbV
  (mercaptans and H2S)
• Calculation of results using a response factor
  (RF)

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Stability Study Results for Canisters
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Stability Study Results for Canisters
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Stability Study Results for Canisters
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Stability Study Results for Canisters
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Stability Study Results for Canisters
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Stability Study Results for Canisters

• Non-H2S Sulfides and thiophene compounds all had
  acceptable recoveries, similar to carbonyl sulfide

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Stability Study Results w/ Deactivation Process

• Canisters were spiked with 100 ppmV thiophene
  during cleaning process.
• No improvement in H2S stability was observed.

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Tedlar Bag Stability Study Results

• Tedlar Bags were spiked at the same concentration
  as canisters
• Acceptable recovery over a 5-day period

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Tedlar Bag Stability Study Results
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Tedlar Bag Stability Study Results
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Statistical Analysis of Response Factors
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Selective Ion Monitoring (SIM)vs. Full Scan Mode

• Refers to mass spectrometer modes of operation
• Full scan detects ions present over range
  (29-260)
• SIM detects specific ions at specific intervals
• Advantages / Disadvantages
• SIM mode increases sensitivity 25-fold
• Cannot do library searches on unknown compounds
  (TICs)
• Can be susceptible to false positives

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Selecitive Ion Monitoring (SIM)vs. Full Scan Mode
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Comparison of Reporting Limits
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System Calibration

• Dimethyl sulfide
• Curve type average RF
• RSD 9.44
• Range 0.5 100 ppbV
• Hydrogen sulfide
• Curve type linear regression
• R2 0.998
• Range 5.0 500 ppbV

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Example Landfill Flare Inlet Analysis

• High ppmV levels of H2S and methane present
• Quantitation of COS, methyl and ethyl mercaptan
  and DMS possible to 500 ppbV
• Re-analysis for speciation of VOCs possible to 10
  ppbV

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Conclusions

• Canister stability poor for mercaptans, H2S
  possibly due to
• Humidity
• FSL coating uniformity
• Reactions between sulfide compounds
• reactive sites in canisters
• Tedlar bag recovery acceptable for all compounds
  over 5 days

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Conclusions

• Reporting limits
• GC/MS limits exceed D5504 limits for non-H2S
  sulfides and thiophenes
• GC/MS limits comparible to D5504 for mercaptans
  and H2S
• No significant gain in sensitivity using SIM,
  further investigation needed

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Questions

• ?