Direct Solvent Extraction Of Solid Samples

An entirely different process of sample-preparation technique involves direct solvent extraction, which is a very simple and convenient technique. Probably the easiest way to do such an extraction is with a Soxhlet extractor. A dried sample such as a spice, chocolate nib, R&G coffee, or a grain can be ground finely and placed in a Soxhlet thimble and extracted with an organic solvent. Either diethyl ether or methylene chloride may be used in such a system. After a number of cycles, the solvent can be combined and concentrated. Nonvolatile organic materials such as lipids, alkaloids such as caffeine and theobromine, and pigments will also be concentrated. The sample may be analyzed directly (with trepidation) or it may be treated as described in the section below, after removal of the solvent. If the sample contained large amounts of lipids (e.g., coffee, chocolate), then the volatiles may be removed by subsequent steam distillation or by a high vacuum stripping technique as described in Sec. VII.

Figure 9 is the GC-MS of a roast and ground coffee sample, which was moistened with water and extracted with methylene chloride in a Soxhlet extractor. The large component eluting at 26 minutes is caffeine.

Table 2 Recovery of Components by SDE from the Model Mixture at a Concentration of 165 ppm (w/v) for Each Compound (Recovery as Percentage of Initial Amount)

Times of SDE

Pressure

1 hr

Atmospheric pressure

4 hr

100 mm Atm

Table 2 Recovery of Components by SDE from the Model Mixture at a Concentration of 165 ppm (w/v) for Each Compound (Recovery as Percentage of Initial Amount)

Pressure

Atmospheric pressure

100 mm Atm

Vol. of solvent

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