STRATEGIES FOR THE ANALYSIS OF CHLOROBENZENES IN SOILS USING SOLID-PHASE MICROEXTRACTION COUPLED WITH GAS-CHROMATOGRAPHY ION-TRAP MASS-SPECTROMETRY

Solid-phase microextraction (SPME) was examined as a possible alternat ive to Soxhlet extraction in the analysis of chlorobenzenes at high co ncentrations (up to 65 mu g g(-1)) in soils. Gas chromatography-ion tr ap mass spectrometry (GC-IT-MS) was used and different strategies were tested in order to obtain suitable responses for chlorobenzenes. Two headspace SPME methods, using fibres coated with polydimethylsiloxane (PDMS) as stationary phase, in splitless and split injection modes, re spectively, and a direct SPME method using 100-mu m PDMS fibre were st udied. For headspace SPME, 7-mu m and 100-mu m PDMS fibres were used a nd good sensitivity was obtained by adding 200 mu l of water to the so il, at a sampling temperature of 30 degrees C and absorption times of 40 and 60 min, respectively. For direct SPME, which involves extractio n of chlorobenzenes from stirred soil solutions using a 100-mu m PDMS fibre, the effect of the addition of different organic solvents, such as methanol or acetone, on the sensitivity and the extraction time was evaluated. The shortest time to reach equilibrium (50 min) was achiev ed when a mixture acetone-water (30:70) was added to the sample. Repea tabilities lower than 8% were obtained for headspace and direct SPME w ith 100-mu m PDMS fibre, whereas for 7-mu m PDMS fibre, repeatabilitie s were slightly higher (between 7 and 11%). The SPME methods were appl ied to the analysis of chlorobenzenes in an industrially contaminated clay soil, CRM-530, which is a candidate reference material. Chloroben zenes in this soil were quantified by standard addition, which led to good reproducibility (R.S.D. between 2 and 10%) for headspace and dire ct SPME with the 100-mu m PDMS fibre and acceptable detection Limits ( 30 to 100 pg g(-1) of soil). The results were consistent with those ob tained in a European intercomparison exercise. (C) 1998 Elsevier Scien ce B.V. All rights reserved.