Laboratory evaluation of porous polymer ORBO 42 and coconut shell charcoal air sampling tubes for sampling styrene vapor

William Brian Johnson, Purdue University

Abstract

Two commonly used media for industrial hygiene air sampling are activated charcoal and porous polymers. A laboratory study was done to compare the relative effectiveness of these two media in terms of their accuracy, precision, Reliable Quantitation Limit (RQL), Coefficient of Variation (C.V.), and stability during sample storage. Based upon a literature review, porous polymers have been used for sampling organic compounds in air and water at very low levels (e.g. in the parts per trillion range) (Beard 1995). Sampling low levels of organic compounds by activated charcoal is difficult because charcoal has a strong affinity for organic compounds and does not easily release them from the media. In contrast, organic compounds are easier to desorb from the porous polymer media. ORBO 42 air sampling tubes, which contain a porous polymer media, may be a more effective for sampling low levels of volatile organic compounds. The sampling media, activated charcoal and ORBO 42 were evaluated with respect to their effectiveness in sampling styrene. A method was developed to generate reliable concentrations of styrene by injecting a specified volume of styrene with an automated microsyringe into an air stream with a constant flow rate. Using this method, concentrations could be generated down to 100 ppb or lower. Samples from the generated concentrations were taken at 50 ml/min as specified by OSHA air sampling method 89. A minimum of five samples were collected at 10, 40 and 100 ppb styrene vapor concentrations. The media were then desorbed (using toluene for charcoal and methylene chloride for ORBO 42) and analyzed by gas chromatography. A statistical analysis found there was no difference between the recovery of ORBO and charcoal media after sampling 40 and 100 ppb vapor concentrations. However, after sampling 10 ppb styrene vapor ORBO 42 continues to recover styrene while the charcoal recovery was consistently zero. The RQL specified by OSHA method 89 was used to evaluate ORBO and charcoal media. The recovery of ORBO media met the OSHA method 89 criteria for RQL which specifies a minimum 75% recovery with a 25% precision or less. The recovery of styrene by ORBO media was 134.2%, 91.9%, and 98.8% with a precision of 24.1, 25.6, and 19.4 after sampling 10, 40, and 100 ppb styrene vapor respectively. The precision of charcoal media after sampling styrene vapor was only below 25% at 100 ppb. At 40 ppb the precision of charcoal media is above 25% (33.53%) which is unacceptable by OSHA method 89. The porous polymer media recovers styrene with better precision, accuracy, RQL, and C.V. when compared to charcoal media after sampling 100 ppb styrene vapor concentrations and lower.

Degree

M.S.

Advisors

Rosenthal, Purdue University.

Subject Area

Environmental Health|Analytical chemistry

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