Heavy metals are among the most hazardous chemical pollutants, present in trace amounts in various samples. Prior to the quantitative measurement of heavy metals in a sample, an effective sample preparation technique is usually adopted. Among the various techniques, dispersive liquid-liquid microextraction (DLLME) is regarded as one of the most effective sample preparation strategies for heavy metal preconcentration due to its simplicity, speed, low cost, high extraction recovery, enrichment factor, and minimal solvent use. Various DLLME modes have been introduced, including ultrasound-assisted DLLME, vortex-assisted DLLME, air-assisted DLLME, spray-assisted DLLME, and effervescence-assisted DLLME, to improve extraction efficiency. In addition, traditional organic solvents are being replaced with alternative solvent systems such as supramolecular solvents (SUPRAs), switchable solvents (SSs), and deep eutectic solvents (DESs) to improve the greenness of these DLLME approaches. Based on the benefits of various DLLME approaches and the use of these environmentally friendly solvents, this review briefly presents the extraction mechanisms and applications of various DLLME modes for heavy metal extraction. In addition, the use of the aforementioned alternative solvents in various DLLME approaches is discussed, along with their benefits. Moreover, the review presents a comparative assessment of different DLLME approaches and environmentally friendly solvents and critically examines limitations, including the use of chlorinated organic solvents in air-assisted DLLME (AA-DLLME), the use of organic solvents for analyte-rich phase dilution, and the use of THF. Furthermore, a table summarizes the figures of merit for all DLLME methods reported (2021-2025) for heavy metal extraction.
Baig et al. (Mon,) studied this question.