EFFECT OF ADDITION OF A GRAPHITIZED CARBON-BLACK TRAP TO A GLASS-BEADS TRAP ON THE CRYOCONCENTRATION OF SOME NONMETHANE HYDROCARBONS IN AMBIENT AIR

Carbotrap was added to a glass beads cryotrap in order to increase the retention of the very volatile two-carbon hydrocarbons, ethylene, eth ane and acetylene. Indeed the obtained recoveries increased from 2 to 3% for ethylene, the poorest retained compound, from 7 to 20% for etha ne and from 23 to 31% for acetylene between the glass beads only and t he Carbotrap/glass beads cryotrap. The addition of the Carbotrap, howe ver, decreased the obtained recovery of o-xylene by 22-46%, depending on the employed conditions. The smaller decrease was observed when the longer desorption time was employed. The variation of the temperature of desorption by 40 degrees C had very little effect on the resulting recoveries. (C) 1997 Elsevier Science B.V.