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ANALYTICAL CHEMISTRY & TESTING SERVICES

Soil Vapour Forum- Charcoal Tubes and Miscellaneous Sampling Methods

presented by Kari Mulroy

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ANALYTICAL CHEMISTRY & TESTING SERVICES

Charcoal Tubes

Charcoal Tubes

• Active sampling with mechanical pumps
• 15 minutes to 8 hours typical
• Flow rate can vary, typically 200mL/min
• Sample time and flow rate dependant on compound

and method selection

• OSHA/NIOSH methods provide guidelines
• Following these guidelines helps prevent breakthrough

problems & over saturation

• Modifications to reference methods must be validated

Charcoal Tubes

• Charcoal extracted/desorbed in solvent

– Commonly carbon disulfide (CS2) but chosen according to compound of interest and method being run, i.e. NIOSH/OSHA methods – 1-2 µL injected into GC/FID or GCMS – 1/500th to 1/1000th of total sample analyzed

Charcoal Tubes

• DL & Sampling Volume Considerations

– DLs are dependant on total sampling volume (sampling time x flowrate). – Typical detection limits for discretes:

• 1 ppmv for 15 minutes x 100 mL/min
• 0.05 ppmv for 8 hours x 100 mL/min
• Lower DLs achievable by GCMS

– Upper limits dependant on breakthrough volume and charcoal tube capacity

• Lighter hydrocarbons breakthrough earlier
• Upper limit ~10,000ppmv for 15 minutes x 100 mL/min,
• r ~200 ppmv for 8 hours x 100 mL/min

Charcoal Tubes

• Advantages

– Reanalysis of samples is possible

• Facilitates dilutions for high samples
• Confirmation by alternate detector possible

– Easily transported – “Back” tube sampled for every sample

• Breakthrough checks always possible

– Moisture is not typically a problem – Tubes and pumps are readily available – Sample stability (≥ 14 days) – Control capacity / max sampling volume by tube size selection – Lower cost method

Charcoal Tubes

• Disadvantages

– Less sensitive than some of other methods – Require higher sampling volume – Shorter list of applicable compounds than TO15/17 – Requires a pump in the field – Note: Speak to the lab about DL requirements. When applying potential attenuation factors charcoal may be appropriate.

Miscellaneous Tubes - XAD

Miscellaneous Tubes - XAD

• PAHs may be sampled on XAD tubes using

NIOSH methods.

• Achievable DLs vary with sampling volume.
• Same advantages / disadvantages as

charcoal method.

Miscellaneous Tubes - DNPH

Miscellaneous Tubes - DNPH

• Acetaldehyde and acrolein can be collected
• n DNPH tubes.
• Analyzed by NIOSH 2018 or EPA TO-11
• Both methods require HPLC analysis and

typically have a DL of 0.5ug per tube.

• Acrolein can be unstable on this media.

Miscellaneous Media – Filter Cassettes / XAD / Silica Gel

Miscellaneous Media – Treated Filters

• Filter cassettes maybe used to collect some

compounds such as chlorine

• Treated filter, analyzed by NIOSH 6011
• Disadvantages:
• Large air volume and flowrate required
• Media is less readily available

Miscellaneous Media – Impingers / Bubblers

Miscellaneous Media – Impingers / Bubblers

• Bubblers can be used as an alternate media

for some substances:

• Acrolein can be collected by a modified CARB 430

which uses toluene in the bubbler to extract the reacted acrolein away from the DNPH solution.

• Hydrogen Cyanide may be collected using a

bubbler, following NIOSH S288

• Alternate method is NIOSH 7904 (soda lime tube)

Miscellaneous Media – Impingers / Bubblers

• Advantages*:
• Typically used only where necessary
• Disadvantages:
• Equipment is fragile
• Handling chemical solutions in the field
• TDG issues

* In some cases, may be the only option to meet required detection limits.

Questions?