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 for 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 performed 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, heating time, purge time and concentration of sodium chloride and the optimum conditions were 4.3 min purge after a sample heating at 46 degrees C for 7.5 min and a sodium chloride solution of 4.3 mol l(-1). In the second method, the soil sample was directly introduced in the test tube for soils, heated and purged. Except for the concentration of sodium chloride, the previous variables 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 with a previously optimised method where soils samples were mixed with an aqueous phase and the VOCs were directly determined by the PT-GC-FID system. (C) 2000 Elsevier Science B.V. All rights reserved.