Focused microwave-assisted soxhlet: an advantageous tool for sample extraction.

A new type of microwave-assisted Soxhlet is here reported. The device uses conventional Soxhlet glassware for solid sample extraction and a focused-microwave digester for irradiation of the sample cartridge at the required intervals while the fresh solvent (condensed vapors from the distillation flask) drips on and passes through the solid sample. In this way breaking of the analyte-matrix bonds is facilitated by application of the appropriate energy. The new approach has been checked in a comparative study by its application to the extraction of analyte families of different polarity (namely, alkanes, polyaromatic hydrocarbons, and herbicides) from the same soil matrix using dichloromethane as extractant. The reduction of the extraction times (from 8 h to 50-60 min, depending on the polarity of the analytes) with efficiency similar to or even higher than that afforded by the conventional Soxhlet technique supports the suitability of the new approach. In addition, recycling of the solvent during extract preconcentration enables minimal environmental contamination to be achieved.