Influence of sediment grain size on the efficiency of focused microwave extraction of polycyclic aromatic hydrocarbons

The efficiency of focused microwave (FMW)-assisted extraction of polycyclic aromatic hydrocarbons (PAHs) at atmospheric pressure was investigated for sediments with different grain size distributions. The PAH contents and distribution profiles obtained by FMW extraction for a dry matrix and a remoistened dry matrix were compared with those obtained by Soxhlet extraction for a bulk matrix and six fractions. The effect of moisture depended on the composition of the matrix and the grain size: an improvement in PAH recovery with the addition of water was noted for coarse fractions, but not for fine fractions. Application to other matrices of different grain sizes and contamination levels showed that FMW-assisted extraction is a good alternative to Soxhlet extraction. FMW extraction efficiency was tested on a naturally moist sediment. PAH concentrations were compared with those obtained by extraction of dry and remoistened dry matrices by FMW extraction and with those obtained by extraction of a dry matrix by Soxhlet extraction. PAH recoveries, compared with those obtained by Soxhlet extraction, were satisfactory. Therefore, it is possible to avoid the drying step with the FMW method. The FMW technique might be suitable for field studies, for example, on a boat during an oceanographic cruise. The developed procedure cosists of an extraction step of 10 min with a few millilitres of solvent, reconcentration steps and micro-column purification. The treatment of the sample can be performed immediately after sampling. The method affords good recovery. The reproducibilities are comparable to, or better than, those obtained by conventional extraction.