Recent advances in stir-bar sorptive extraction: Coatings, technical improvements, and applications

Stir-bar sorptive extraction (SBSE) is a popular solvent-less sample preparation method, which is widely applied for the sampling and preconcentration of a wide range of non-polar solutes. A typical stir-bar for SBSE is composed of a polydimethylsiloxane (PDMS) film, coated onto a glass jacket with an incorporated magnet core. Sampling is carried out by direct immersion or by exposing the stir-bar to the headspace of the sample. To-date the majority of reported SBSE devices have used PDMS as the sorbent, with a few alternative commercially SBSE coatings available (such as polyethylene glycol and polyacrylate), which limits the applicability of SBSE to more polar and hydrophilic solutes. The interest in more selective extraction has been the driving force behind the recent development of novel SBSE coatings, particularly those exhibiting selectivity towards more polar solutes. During the last decade, a significant number of novel SBSE coatings were introduced utilising different fabrication approaches, including surface adhesion, molecular imprinting, sol-gel technology, immobilised monoliths, and solvent exchange processes. A range of nano- and micro-carbon-based materials, functional polymers, metal organic frameworks (MOFs), and inorganic nanoparticles have been employed for this purpose. Some of these SBSE coatings have exhibited higher thermal and chemical stability and delivered wider selectivity profiles. This review aims to summarise these significant developments, reported over the past six years, with specific attention to novel materials and selectivity for extending the potential applications of SBSE.