Two decades of stir bar sorptive extraction: A retrospective and future outlook

Stir bar sorptive extraction (SBSE) has been developed nearly 20 years ago and was commercialized as Twister very soon after its introduction. Main appreciated features by its users are the solventless extraction, predictable extraction efficiencies, very high sensitivities when applied in combination with thermal desorption (TD) - GC-MS, multiple use for determinations in gaseous and aqueous matrices and excellent repeatability and reproducibility when polydimethylsiloxane (PDMS) is applied as sorptive phase. These features originate from the unique characteristics of PDMS, with low glass transition temperature, very low bleeding profile at high temperatures after appropriate conditioning, and excellent diffusivity and permeability. PDMS-SBSE is intensively applied in different areas (environmental, food, biofluids, drugs, etc.) for sensitive determinations of solutes with a log P larger than 3. Of utmost importance for routine application of SBSE are its figures of merit and several studies have illustrated that SBSE on PDMS can be validated and standard operating procedures developed. For more polar solutes, different derivatization methods have been applied to enhance the hydrophobicity of the solutes and thus increasing the log P value. Over the years, other coating materials have been evaluated and/or developed for enhanced extraction of more polar compounds. Only a limited number, however, are operating in the sorptive or partitioning mode while only few of them have favorable thermal characteristics to be used in TD-GC-MS applications. To the best of our knowledge, only one has been commercialized namely a PDMS/ethylene glycol (EG) copolymer placed on an inert metal grid for mechanical stabilization. Other home-made coatings, such as monoliths, polyurethane foams or other polymers are mostly used in combination with liquid desorption, are not commercially available in ready-to-use stir bar format and, therefore, not accessible for independent in-depth testing. Alternatively, two other methods applying PDMS stir bars were recently developed to extend SBSE to more polar solutes: solvent assisted SBSE (SA-SBSE) and ice concentration linked with extractive stirrer (ICECLES) that is based on freeze concentration. This review on SBSE is highlighting both developments and future perspectives of SBSE are outlined. (C) 2018 Published by Elsevier B.V.