Presentation Abstract

Title: Evaluation of a Direct-Sampling Instrument for Detecting Benzene in a Mixed-Hydrocarbon Environment

Author: Marc J. Plisko, CIH, John W. Spencer, CIH, CSP, and Adam Keil, PhD

Presented at: AIHce 2011, Portland, Oregon

Many of the direct-reading gas detection instruments in use today are calibrated to standards other than benzene and rely on correction factors for reporting benzene air concentrations.  The objective of the work presented herein was to evaluate the efficacy of a portable direct-sampling mass spectrometer for measuring benzene concentrations in a mixed-hydrocarbon environment.  The method of evaluation employed the direct-sampling mass spectrometer in conjunction with Summa canisters to measure the airborne mass concentration of benzene evaporating from a solution of mixed organic solvents.  The solution was evaporated from a glass plate under controlled environmental conditions in an isolated glove box and air duct system.   Air samples of the solvent vapor were obtained through sampling ports located approximately 4.75 meters downstream from the glove box.  The direct-sampling mass spectrometer incorporated a cylindrical ion trap mass analyzer (CIT) for separating ions according to their mass-to-charge ratios.  Twenty five one-liter Summa canister samples were collected serially during the 19-minute evaporation period and were analyzed via EPA Method TO-15.  Comparison of the results between the instrument recordings and Summa canister analysis revealed a correlation coefficient and covariance 0.95 and 20, respectively, indicating strong association between the data.   The actual measured data showed that, although there was strong correlation, the values of the instrument recordings were consistently less than the Summa canister data by approximately 50%.  It was subsequently determined that approximately one half of the evaporated benzene was being quantified at the CIT detector.  Additional evaporation trials involving pure benzene and the individual organic solvents indicated that the ionization of cyclohexane, present in the organic solvent mixture, resulted in signal suppression at the CIT detector.   The authors conclude that while the data exhibited strong correlation, further investigation is proposed in order to fully characterize the magnitude of observed signal suppression.

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