Ronald E. Majors

For more intimate contact between solvent, the adsorbed (absorbed) analyte and matrix, other sample preparation techniques might be required. Several methods that can achieve this intimate contact include homogenization, sonication, emulsification, or vortexing. For biological samples, various cell disruption techniques can be employed. All of these methods require the application of an additional external force (or forces) to the sample in suspension.

Table I: Most modern solid extraction techniques use increased temperature and pressure

Modern Soxhlet Extraction

Soxhlet extraction is by far the most widely used method for solid sample pretreatment. In fact, it is the de facto standard with which all other extraction procedures are compared and contrasted. Soxhlet extraction is simple, effective, and relatively inexpensive. Generally, it provides good analyte recovery but its traditional operation is slow and uses copious amounts of solvent. Although classical Soxhlet extractions can last as long as 18–24 h, once set up and running, the experiment requires very little user involvement. Small-volume Soxhlet systems are available, but the sample size often is dictated by the analyte concentration, the necessary mass to obtain a representative sample, and the chromatography detector sensitivity, all of which could combine to require a larger sample size.