AMBIENT AIR ANALYSIS OF VOCs AND HALOCARBONS BY AN AMBIENT TRAPPING TECHNIQUE

摘要

The ability to concentrate components from ambient air gives the environmental researcher the ability to see components at levels that are lower than the lower detection limits of the detector in use. Currently a large majority of concentration methods involve the use of cryogenic liquids to cool the trap to a temperature that allows trapping of light volatile organics from the air. The use of cryogenics increases cost and requires a space to contain cryogenic liquids. The focus of our research has been to eliminate the need of cryogenic liquids from the process of concentration. Wasson-ECE Instrumentation has developed an air concentrator designed to collect volatile organic compounds (VOCs) and halocarbons on a sorbent trap at ambient temperatures. The sorbent trap exhibits up to a 500-fold concentration effect at ambient temperatures without the use of cyrogenic liquids. The analytes are drawn onto the trap from ambient air, tedlar bags or from SUMMA canisters pressurized up to 30 psig. When the air is pulled through the trap the target analytes are concentrated on the trap. The trap is then dry purged with helium to remove components that may interfere with the analysis such as, oxygen, nitrogen, argon, carbon dioxide and water. Once the trap has been dry purged, it is heated to a set desorb temperature, and the target analytes are carried by helium from the sorption material to the gas chromatograph. High-resolution capillary chromatography is used in combination with either a mass spectrum detector (MSD) or a flame ionization detector (FID) to speciate the target analytes. VOC reporting limits vary depending on GC methodology as well as reactivity of the target analytes to the sorbent material. This technique has yielded reporting limits of 5 ppbv for HRVOCs on an FID, and reporting limits of 0.1 to 0.5 ppbv for VOCs on the EPA Method TO-15 analysis by GCMS.