Progress of Extraction Solvent Dispersion Strategies for Dispersive Liquid-liquid Microextraction

Dispersive liquid-liquid microextraction (DLLME) is a new sample preparation technique emerging recently. The dispersion of organic extraction solvent at micro-liter level in aqueous samples is the key step in DLLME. The published strategies of dispersion for DLLME are roughly classified into three types in terms of the instruments used and dispersion principles, namely physical dispersion method, in-situ chemical reaction-based dispersion method and new dispersion medium-based dispersion method. The physical dispersion method includes mechanical shaking method, ultrasound/microwave-assisted method and solubility-adjustment method. The in-situ chemical reaction method is referred to the two modes, in which either the dispersed extraction solvent is formed by in-situ chemical reaction or the dispersion of extraction solvent is achieved by the gas generated from chemical reactions. The new dispersion medium-based dispersion method uses some non-volatile substances, such as medium-chain saturated fatty acids, ionic liquid, surfactant and kapok fiber fragments, to substitute the dispersive solvent used in conventional DLLME. A total of 96 relevant literatures are cited in this review and the prospects of DLLME are highlighted.