Strategies for the analysis of chlorobenzenes in soils using solid-phase microextraction coupled with gas chromatography–ion trap mass spectrometry.

Abstract

Solid-phase microextraction (SPME) was examined as a possible alternative to Soxhlet extraction in the analysis of chlorobenzenes at high concentrations (up to 65 μg g −1) in soils. Gas chromatography–ion trap 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, respectively, and a direct SPME method using 100-μm PDMS fibre were studied. For headspace SPME, 7-μm and 100-μm PDMS fibres were used and good sensitivity was obtained by adding 200 μl of water to the soil, at a sampling temperature of 30°C and absorption times of 40 and 60 min, respectively. For direct SPME, which involves extraction of chlorobenzenes from stirred soil solutions using a 100-μm 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 achieved when a mixture acetone–water (30:70) was added to the sample. Repeatabilities lower than 8% were obtained for headspace and direct SPME with 100-μm PDMS fibre, whereas for 7-μm PDMS fibre, repeatabilities were slightly higher (between 7 and 11%). The SPME methods were applied to the analysis of chlorobenzenes in an industrially contaminated clay soil, CRM-530, which is a candidate reference material. Chlorobenzenes in this soil were quantified by standard addition, which led to good reproducibility (R.S.D. between 2 and 10%) for headspace and direct SPME with the 100-μm PDMS fibre and acceptable detection limits (30 to 100 pg g −1 of soil). The results were consistent with those obtained in a European intercomparison exercise.