MultiSimplex optimisation and comparison of different purge-and-trap extractions of volatile organic compounds in soil samples

Two different purge-and-trap (PT) extraction methods have been optimised fo r nine volatile organic compounds (VOCs) (benzene, toluene, chlorobenzene, ethylbenzene, m-xylene, o-xylene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and 1,2-dichlorbenzene) making use of the simplex method implemented in the MultiSimplex program. In both cases, the determination of the VOCs was per formed by a coupled GC-FID system. In the first extraction method the soil sample was sonicated with methanol and 100 ml of the extract were analysed as an aqueous sample. Variables considered were heating temperature, heatin g time, purge time and concentration of sodium chloride and the optimum con ditions were 4.3 min purge after a sample heating at 46 degrees C for 7.5 m in and a sodium chloride solution of 4.3 mol l(-1). In the second method, t he soil sample was directly introduced in the test tube for soils, heated a nd purged. Except for the concentration of sodium chloride, the previous va riables were also considered and the optimum conditions were 51.1 min purge after 32.6 min heating at 61 degrees C. These two methods are compared wit h a previously optimised method where soils samples were mixed with an aque ous phase and the VOCs were directly determined by the PT-GC-FID system. (C ) 2000 Elsevier Science B.V. All rights reserved.