Atmospheric volatile organic compounds (VOC) and air toxic concentrations are normally measured using some type of gas chromatography. Since these concentrations are often very low, some type of concentration technique is normally employed. This may be done at the monitoring site, by collecting an air sample in an adsorbent cartridge, or in the laboratory where canister samples may be cryogenically focused before injection into the chromatograph. EPA has specified the methods TO-14 for VOCs and TO-15 for air toxics. Collection and shipment of air samples in this fashion results in sensitive and detailed analysis for speciated organic compounds, but is time consuming and expensive and always carries the potential for sample loss or modification. Expense alone has limited widespread monitoring for these compounds.
For several years now my research group has been developing a new technique for on-site VOC monitoring which does not require the adsorbent step. We call this technique pneumatic focusing, as it involves raising the sample pressure to 600 psi or more before injection onto the chromatographic column, also maintained at high pressure. The pneumatic focusing step both concentrates the sample and removes water vapor by condensation. We have modified a commercial FID-GC for pneumatic focusing and used a commercial open tubular alumina column to monitor ambient VOCs in Portland, Oregon for more than a year, acquiring more than 15,000 samples with sensitivities down to 50 ppt for benzene. Technical details and performance of this technology will be described, potential applications discussed, and a prototype demonstrated.
Robert O'Brien received a Ph.D. in Physical Chemistry from the University of Florida and worked for ARB in downtown Los Angeles and at the El Monte laboratories as an Air Pollution Research Specialist in the early 1970's. He has been a professor of Chemistry and Environmental Science at Portland State University since then and has been involved in laser measurements of atmospheric free radicals for many years. His laboratory developed the FAGE (low pressure) technique for HO, HO2, RO2 and NO2 measurements. This technique is now employed by researchers in the United States, United Kingdom and Japan. While making radical measurements in Riverside during SCOS-97, his group was compelled to make ancillary, manual, cryofocusing, and VOC measurements for almost a month. This intimacy with cryofocusing led him to search for a "better way" for automated VOC measurements, leading eventually to a patent application by PSU for pneumatic focusing. With current and former students and associates, he has formed VOC Technologies for the commercialization of this technology. VOCTEC is currently working on automated breath analysis with a combined Phase 1 and 2 SBIR grant from NIEHS, apparently the first such fast-track grant awarded.
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