Applications of layered double hydroxides in sample preparation: A review

Microextraction is a technique that can be used to selectively extract substances from a complex matrix using small amounts of extracting agents and/or solvents. The technique can be broadly classified into liquid- and solid-phase microextraction methods, according to the specific nature of the system. The principle of the solid-phase microextraction (SPME) is founded on selective equilibrium-based extraction of compounds using a microporous adsorbent that acts as a solid phase extraction (SPE) sorbent. In recent years, there has been growing interest in the use of layered double hydroxides (LDHs) as microextraction sorbents. The main advantages of using LDHs are their high surface area to volume ratio, low operating pressure, and simplicity of fabrication and purification. They are also relatively inert and easy to purify by simple washing. Several recent studies have shown that LDHs are good candidates for drug delivery, catalysis, environmental remediation, energy storage and chemical analysis. The use of LDH in analytical chemistry includes sensing, electrochemical analysis, and extraction. In this review, the roles of LDHs in solid phase extraction and microextraction including dispersive-solid phase microextraction (dSPME), in-tube solid phase microextraction (IT-SPME), headspace solid phase microextraction (HS-SPME), stir bar sorptive extraction (SBSE) and thin film microextraction (TFME) were discussed. The preparation, characterization, regeneration and analytical performances/applications were also discussed.