Simple laboratory-made system for the determination of C2-C7 hydrocarbons relevant to photochemical smog pollution.

A simple gas chromatographic system suitable for determining volatile organic compounds from C2 to C7 in air is described. It consists of a capillary cold trap filled with graphitic carbon, a thermodesorbing device, a capillary gas chromatograph equipped with an alumina column and a flame ionization detector. Dry, as well as humid, air samples can be analysed with our system. Up to 2-1 samples of air can be enriched on our trapping device by using Nafion membranes for removing water. Direct analysis of air samples is possible by enriching 250 ml on the carbon trap. The recovery, sensitivity and linearity of our system have been checked with standard mixtures and real samples. The performances have been compared with those afforded by a commercially available instrument exploiting a different enrichment procedure. The results obtained show that our analyser can be successfully applied to determinations of C2 to C7 hydrocarbons present in air samples at levels of 0.01 ppb (v/v).