Review on Processes in Liquid-Liquid and Solid Phase Extraction

Abstract

Abstract: The process of separating a component of mixture of liquid using liquid solvent is known as solvent extraction. The component being separated is completely insoluble in the solvent known as the carrier liquid. Distribution coefficient and partition coefficient are used to quantitatively determine the degree of solubility of a solute in a solvent compared to its solubility in another solvent. In liquid-liquid extraction (LLE) the solvents used should have maximum transfer of solute from carrier into the solvent. The solvent used must have high affinity for the solute to be extracted and it must not be completely miscible with the carrier liquid. Solid phase extraction (SPE) is a solvent-extraction system with a stationary phase by adsorption onto a solid support (usually silica) and the other liquid phase which is mobile. It uses small membranes or columns and many of the extracting agents used in LLE are also used in SPE. SPE generates less amount of wastes and it is an excellent substitute for LLE as it is faster and more efficient. It requires samples as small as 50 – 500ul and relatively small volumes of solvents not as pure as may be required by LLE. The working principles of SPE are like that of LLE were partitioning takes place between two immiscible liquids but in SPE the analytes to be extracted are partitioned between liquid and solid. This paper has reviewed the various processes involved in solvent extraction considering diluents in solvent extraction, liquid-liquid extraction and solidphase extraction.