Evidence for selectivity of absorption of volatile organic compounds by a polydimethylsiloxane solid-phase microextraction fibre

Solid-phase microextraction using a 30 mu m polydimethylsiloxane fibre has been used to sample the volatile organic compounds from standard mixtures a nd from mixtures produced by the decomposition of organic compounds. This m ethod of sampling has been compared with the direct injection of an aliquot of headspace gas and shows an enrichment factor of approximately 100 over a 1 ml gas injection for organosulphur gases such as dimethyldisulphide. Th e performance of the fibre has been evaluated with respect to accuracy and precision at several concentrations in representing the composition of mult icomponent mixtures. It was found that the presence of a second component i n a gas sample reduced the capacity of the fibre to absorb the primary comp onent. The selectivity of the fibre for various volatile compounds with dif fering functionality was also studied. It was found that the non-polar poly dimethylsiloxane fibre preferentially absorbed the non-polar components of a mixture, e.g nonane and, correspondingly, under reported the more polar c omponents, e.g. ethanol. Hence, the fibre discriminates in favour of non-po lar and against polar components in a mixture in comparison with direct ana lysis of a headspace sample. Thus, quantitation of a component in a multi-c omponent mixture is liable to error from competitive interference from othe r components. A major advantage of the technique, however, is that it does not absorb, and therefore introduce, water into the analytical system. (C) 2000 Elsevier Science B.V. All rights reserved.