Solid-phase extraction combined with dispersive liquid-liquid microextraction for the analysis of glucocorticoids in environmental waters using liquid chromatography-tandem mass spectrometry

This paper illustrates an enrichment procedure based on the combination of solid phase extraction (SPE) with dispersive liquid-liquid microextraction (DLLME) for the determination of ng/L concentration levels of glucocorticoids in river water samples. In SPE-DLLME, the target analytes were adsorbed by loading a large volume sample (200 mL) into an OASIS HLB cartridge (60 mg). After their desorption with a small volume of ethyl acetate (500 µL), this eluate was used as the dispersant in the following DLLME, performed on 5 mL of water, using a low transition temperature mixture (LTTM) as the extractant (100 µL). The LTTM was obtained by the heat-mixing of choline chloride and sesamol in a molar ratio 1:3 (ChCl:Ses, 1:3); when cooled, it was liquid at room temperature, denser than water and immiscible with it. The SPE-DLLME approach significantly limits the use of high volumes of organic solvents, avoids the evaporation step, and allows one to achieve an enrichment factor greater than 2500. All extracts were analysed by high-performance liquid chromatography-electrospray-tandem mass spectrometry. Eleven glucocorticoids, including the epimers dexamethasone/betamethasone, were separated on a polysaccharide-based column, based on cellulose tris(3‑chloro-4-methylphenylcarbamate) chiral selector. Recoveries ranged from 68 to 100% (spike level of 5 and 20 ng/L), with a LOD of 0.21-1.39 ng/L and a LOQ of 0.69-4.17 ng/L. The intra-day precision and inter-day precision were lower than 15%. After optimization and complete validation, the method was applied to analyze surface water samples, taken from River Tiber, to evaluate the effective applicability of the procedure and to establish the contamination levels for these substances.