Extraction (chemistry)

Laboratory-scale liquid-liquid extraction. Schematic of a separatory funnel used for laboratory scale (<2L combined volume) extractions of 2 immiscible liquid phases, where "oil" may be any phase less dense than water (typically an organic solvent) and "water" may be any less dense liquid phase, typically an aqueous phase.

Extraction in chemistry is a separation process consisting in the separation of a substance from a matrix. It includes Liquid-liquid extraction, and Solid phase extraction.

Types of extraction

There exist several types of extraction, including: liquid-liquid extraction, solid-phase extraction, solid-phase microextraction, Soxhlet extraction, fizzy extraction.

Components of an extractive process

Extractions often use two immiscible phases to separate a solute from one phase into the other. Typical lab extractions are of organic compounds out of an aqueous phase and into an organic phase. Common extractants are arranged from ethyl acetate to water (ethyl acetate < acetone < ethanol < methanol < acetone:water (7:3) < ethanol:water (8:2) < methanol:water (8:2) < water) in increasing order of polarity according to the Hildebrand solubility parameter. The extract can be put back to dried form using a centrifugal evaporator or a freeze-drier.

Theory of an extraction between two phases

The distribution of a solute between two phases is an equilibrium condition described by partition theory. This is based on exactly how the analyte move from the water into an organic layer

Modern variations

Techniques include supercritical carbon dioxide extraction, ultrasonic extraction, heat reflux extraction, microwave-assisted extraction, instant controlled pressure drop extraction (DIC), and perstraction.

Applications

Boiling tea leaves in water extracts the tannins, theobromine, and caffeine out of the leaves and into the water. Solid-liquid extractions at laboratory scales can use Soxhlet extractors (such as oil from olive cakesee at right).

References