Technique for Monitoring Toxic VOCs in Air:  Sorbent Preconcentration, Closed-Cycle Cooler Cryofocusing, and GC/MS Analysis

An automated gas chromatographic (autoGC) system was used to collect and analyze both nonpolar and polar volatile organic compounds (VOCs) in ambient air. This system combines the use of dual multiadsorbent traps to provide continuous air sampling for 57 min of each hour; a dry helium purge to remove extraneous gases, including some residual water vapor retained in the sorbent packing; thermal desorption of analytes onto a VOC-focusing trap cooled by a small Stirling-cycle refrigerator; and GC/mass spectrometric detection using ion trap technology. Cleanliness, linearity, method detection limits (MDLs), precision, and accuracy of the autoGC were determined for 41 VOCs. For most of the compounds tested, MDLs were less than 0.10 ppbv, response was linear over the 1−40 ppbv range, accuracy was ±20%, and trap-to-trap precision was ±20%. Linear response for a set of polar VOCs was also determined over the 5−50 ppbv range. The autoGC was successfully operated in a mobile laboratory at a field site in Axis, AL, for 10 days, during which time the system was in operation 24 h/day with minimal interruptions. This autoGC is designed for monitoring subsets of the 97 VOCs among the 189 hazardous organic compounds that are listed in Title III of the Clean Air Act Amendments of 1990.