USE OF ADSORBENTS TO COLLECT SELECTED HALOCARBONS AND HYDROHALOCARBONS OF ENVIRONMENTAL INTEREST FROM LARGE AIR VOLUMES

Hydrohalocarbons are the proposed replacement compounds for the chloro fluorocarbons. They will initially have very low concentrations, on th e order of a ppt (v/v), in the global atmosphere. Neither gas chromato graphy-electron-capture detection, nor gas chromatography-mass spectro metry, have adequate sensitivity to measure such concentrations direct ly from air samples; concentration techniques are required to achieve this. We have examined a range of commercially-available adsorbents, i ncluding activated charcoals, carbon molecular sieves, porous polymers , and graphitized carbons, for their suitability as ambient temperatur e concentrating traps for a range of man-made halocarbons and hydrohal ocarbons (CFC-12, CFC-11, CFC-13, HCFC-22, HCFC-123 and HFC-134a). Fro m our measurements of specific retention and desorption volumes it was found that no one adsorbent could both collect all of the target comp ounds with high efficiency, and also allow efficient recovery by therm al desorption. A sequence of adsorbents is required. We designed a 30 cm long x 0.64 cm O.D. trap containing HayeSep D(B) (a porous polymer) , Carboxen 1000 and Carbosieve S-II (both carbon molecular sieves) to collect all of the target compounds from a 5 1 air sample at 25-degree s-C and allow efficient recovery with 500 ml of nitrogen carrier gas a t 200-degrees-C. Good comparability was demonstrated between the adsor bent trapping system and direct loop injection analysis for CFC-12 in ambient air. Precision for all of the compounds analyzed with the adso rbent trap was better than 4%, and improved to better than 1% when rat ioed to CFC-12.