USE OF SOLID-PHASE EXTRACTION IN THE DETERMINATION OF BENZENE, TOLUENE, ETHYLBENZENE, XYLENE AND CUMENE IN SPIKED SOIL AND INVESTIGATION OFSOIL SPIKING METHODS

A method has been developed for the determination of benzene, toluene, ethylbenzene, xylene and cumene (BTEXC) in soils, based on methanol e xtraction, solid-phase extraction (SPE) of the diluted extract and gas chromatography. Quantitative recoveries of BTEXC were obtained from m ethanol extracts provided the solvent composition was adjusted to meth anol-water (50 + 50) prior to SPE, and care was taken to avoid the dev elopment of headspace into which analytes could partition, Cartridge ( 500 mg) load volumes of up to 20 ml of methanol-water extract were pos sible for all the analytes, except benzene (7 ml), without significant loss due to volatilization. The minimum elution volume for 100% remov al of the analytes from the SPE cartridge was 1.5 ml of dichloromethan e, It was possible to recover >90% of analytes added as a concentrated methanolic solution to a dry, clay soil, but the recoveries decreased if field-moist soil was used and if the soil was spiked with petrol, Recoveries were also reduced if the soil and spiking solution were lef t in contact for extended periods (as would occur in the event of a re al contaminant spillage), Over a 17 d period, more than 30% of the BTE XC added to a soil as a dilute solution in methanol-water (50 + 50) be came too tightly bound for removal by a single aliquot of extractant, When the method of vapour fortification was used to produce performanc e evaluation materials, both uptake of BTEXC and stability of the anal yte concentrations after spiking were found to depend strongly on the soil type.