Shake flask extraction Soxhlet and ultrasonic extraction

The extraction of solid samples is most commonly done using traditional liquidsolid extraction methods such as shake flask extraction, classical Soxhlet extraction (introduced in 1870!) and its more modern forms Soxtec and Soxtherm. Soxhlet extraction is still considered as a rugged method because it has very few variables that can adversely affect extraction recovery. The modern forms allow equivalent extraction efficiency in about 2 h. It is not the aim to detail all these methods but rather to concentrate on ultrasonic extraction (UE).

UE uses mechanical energy in the form of shearing action that is produced by a low-frequency sound wave. The sample is immersed in an ultrasonic bath with a solvent and subjected to ultrasonic radiation for 15-60 min. UE often provides very good results for solid food samples. Advantages over other techniques are simplicity, speed, productivity and low cost. The selection of the solvent is of utmost importance and heating can be applied if needed although self-heating is already generated by the sonication process. Its application will be illustrated and its performance compared to microwave assisted solvent extraction (MASE) and accelerated solvent extraction (ASE) for the analysis of PCBs in food samples (Section 3.2.6).

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