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 dis tribution profiles obtained by FMW extraction for a dry matrix and a remois tened dry matrix were compared with those obtained by Soxhlet extraction fo r a bulk matrix and six fractions. The effect of moisture depended on the c omposition 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 fin e fractions. Application to other matrices of different grain sizes and con tamination 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 ex traction of dry and remoistened dry matrices by FMW extraction and with tho se obtained by extraction of a dry matrix by Soxhlet extraction. PAH recove ries, compared with those obtained by Soxhlet extraction, were satisfactory . Therefore, it is possible to avoid the drying step with the FMW method. T he FMW technique might be suitable for field studies, for example, on a boa t during an oceanographic cruise. The developed procedure cosists of an ext raction step of 10 min with a few millilitres of solvent, reconcentration s teps and micro-column purification. The treatment of the sample can be perf ormed immediately after sampling. The method affords good recovery. The rep roducibilities are comparable to, or better than, those obtained by convent ional extraction.