Liquid-Liquid extraction is a method by which a compound is pulled from solvent A to solvent B where solvents A and B are not miscible. The most common method of liquid-liquid extraction is performed using a separatory funnel.
Separatory Funnel extractions are performed to extract compounds either into or from an aqueous layer (typically).
Compounds which are poorly miscible in organic solvents but highly miscible in water can be extracted into organic compounds either by (1) repetitive extraction with a separatory funnel or (2) by using a liquid-Liquid extractor.
Extraction methods differ depending upon the density of the solvent being used. Solvents more dense than water will require different glassware (or supplemental glassware) vs. solvents that are less dense than water. There are presently a number of setups that can do both. By adding a removable fritted glass tube, and closing the solvent return tap, the setup below can be used to extract water continuously with a solvent less dense than water (such as diethyl ether).
Using a setup purchased from Sigma-Aldrich, the method can be accomplished as deplicted below in the extraction of methylene blue from water into methylene chloride:
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