Extraction of compounds of interest from bio-based materials

Extraction of compound(s) of interest covers a broad spectrum of applications in the laboratory and industrial field: from natural active ingredients (e.g. flavours, pigments, oils, vitamins, antioxidants, proteins, etc.) for pharmaceutical and food industry to contaminants and environmental pollutants (pesticides, polycyclic aromatic hydrocarbons – PAHs, polychlorinated biphenyls – PCBs, etc.) for environmental authorities. Bio-based or environmental materials (e.g. plant tissues, wood, soil) include various components whose interaction can cause undesired interferences and result in misinterpretations in quantitative and/or qualitative analyses.

The main purpose of extraction techniques is thus to gain analyte compounds (or more compounds of interest):
 * 1) in high yield;
 * 2) with the highest purity without interferencing compounds;
 * 3) with low waste; and
 * 4) with low energy/time consumption at the same time.

In general, extraction techniques are based on a separation principle, „like dissolves like“. For selecting an appropriate extraction system, the following conditions are crucial: solvent type, sample/solvent ratio, temperature, pressure, extraction duration and number of extraction cycles.

Common techniques use solid or semi-solid samples, so compounds of interest are dissolved into suitable solvents or more solvents in a row (solid-liquid extraction) or are proceeded in liquid form within liquid-liquid extraction. Liquid-liquid extractions are often performed to purify the analyte. However, this separation is possible only when the compound(s) of interest is soluble in a different solvent than the undesired compound(s). At the same time, those two solvents have to be mutually immiscible. The extraction procedures might be combined in sequences as a part of the purification step or to concentrate the amount to increase the analyte detectability.

More advanced techniques belong to solid-phase extraction (SPE) using retention of analyte on a sorbent; accelerated-solvent extraction (ASE); ultrasound-assisted extraction (UAE); microwave-assisted extraction (MAE); enzyme-assisted extraction; and supercritical fluid extraction (SFE) by application of supercritical carbon dioxide.

The conventional solid-liquid extraction system counts the Soxhlet apparatus. A more sophisticated system that offers time-planning is an updated Soxhlet - PC-controlled extraction system fexIKA. A more time-effective system is accelerated solvent extraction (ASE). It is an automated solid-liquid extraction system that uses 100 times higher pressure than conventional techniques and, therefore, enables low solvent consumption with the advantage of considerably shorter extraction time.