Indirect determination of low vapour pressures using solid-phase microextraction-application to tetrachlorobenzenes and tetrachlorobenzyltoluenes

There is still a gap of reliable vapour pressure data at ambient temperature for low volatile organic substances due to the difficult and time-consuming determination using the classical methods. Static headspace extraction with a solid-phase microextraction (SPME) fibre in combination with gas chromatographic analysis provides an inexpensive tool for the indirect determination of low vapour pressures down to 10−5 Pa. The procedure consists of two steps: (a) exposure of SPME fibre in the headspace above the test chemical over minutes to hours and (b) desorption and quantification of extracted amount. The calibration was performed using low volatile reference substances with well-known vapour pressures. A good correlation was found between substance uptakes of SPME fibre and vapour pressures. The method was applied, e.g. to tetrachlorobenzenes and to selected tetrachlorobenzyltoluenes with questionable vapour pressures. We obtained values between 0.98 and 13.5 Pa for the former and results between 0.13 and 0.68 mPa for the latter group of congeners. The scope of the method can be extended to substances with even lower vapour pressures, provided that reliable reference data are available.