Recent elaborations in electromembrane microextraction technique for preconcentration of chromium species: A mini-review

In recent years, electromembrane microextraction techniques have been used widely for the analysis of chromium species (trivalent and hexavalent chromium) in different environmental matrices. It is based on the electrokinetic migration across a membrane under the effect of an external electrical field between two aqueous phases. Trace analysis in complex matrices usually requires an effective sample preparation step to isolate, extract, and enrich the target analytes. Due to its distinctive qualities, including a high degree of enrichment factors, clean-up, and conformity with green chemistry principles, electromembrane microextraction techniques are among the methods for extracting chromium that have gained much attention in recent years. These techniques could be classified into two groups; electromembrane extraction (EME) which is based on using hydrophobic compounds (e.g., a few microliters of organic solvents) to separate the two aqueous solutions (donor and acceptor solutions), and gel electromembrane microextraction (G-EME) which is based on using a membrane made of biopolymers. In this review, the most recent advancements in EME and G-EME technologies for the extraction of chromium species in environmental samples in the last five years were summarized. Furthermore, the performance of the systems is evaluated in terms of their precision and accuracy, detection limits, and merits and drawbacks. Finally, future perspectives on these techniques were discussed.