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(T/EH094) A new method for indirect determination of low vapour pressures. Paschke, Albrecht1, Schröter, Uwe1, Schüürmann, Gerrit1, 1 ABSTRACT- The saturation vapour pressure (P) is a physicochemical key parameter for modelling fate and transport of persistent organic pollutants in the environment. There however is a gap of reliable data at ambient temperature for low volatile organic substances due to the difficult and time-consuming determinantion by using e.g. the gas saturation method. Static headspace extraction with a polymer-coated fused silica fibre in combination with gas chromatographic analysis provides a new inexpensive and efficient tool for the indirect determination of vapour pressures down to 0.1 mPa. We used a commercial solid-phase microextraction (SPME) device with a Carbowax/Divinylbenzene coating (from Supelco). The two-step procedure [i.e. 1) the exposure of SPME fibre in the saturated headspace above the test chemical and 2) the desorption and quantification of extracted amount] was calibrated using low volatile reference substances with well-known vapour pressures (selected chlorobenzenes, polychlorinated biphenyls, hexachlorocyclohexane isomers, and DDT with its metabolites). A good linear correlation was found between uptake rate of the SPME fibre and vapour pressure. The calibrated method was applied e.g. to tetrachlorobenzenes and to selected tetrachlorobenzyltoluenes (TCBTs) with questionable P values. Our results for the TCBTs are between 0.4 mPa and 1.2 mPa and thus in the order of the data obtained by van Haelst et al. [J. Chromatogr. A 727 (1996) 265] using the relative retention time method with DDT as reference substance. In addition, our results are comparable with predicted values bases on a new vapour pressure model published by Kuehne et al. [Chemosphere 34 (1997) 671]. Key words: Vapour Pressure, Solid-Phase Microextraction, Chlorinated Hydrocarbons |
