Fully Automated Water Sampling-Surfactant-Enhanced Membrane Bag Liquid-Phase Microextraction-Ultrahigh Performance Liquid Chromatography-Mass Spectrometry.

Abstract

A fully automated integrated analytical platform that included continuous water sampling, sample preparation (extraction), and analysis for the determination of nine glucocorticoids was developed. A peristaltic pump was employed to deliver the water sample automatically. The subsequent sample preparation and analytical processes were also fully automated with the use of a commercial autosampler unit coupled to an ultrahigh performance liquid chromatography-tandem mass spectrometric system. The sample preparation step involved membrane bag liquid-phase microextraction in which a synergistic mixture of n-octanol enhanced with surfactant sodium dodecyl sulfate (SDS) (0.10% in n-octanol) was applied as the extractant phase. Addition of SDS helped to improve the extraction, increasing enrichment factors (EFs) by severalfold compared with the use of n-octanol only as extractant solvent. Various parameters to improve extraction efficiency were evaluated. They included percentage of surfactant used, sample pH, agitation rate, extraction duration, salting out effect, extraction temperature, and flow rate for sample introduction. Under the most favorable conditions, enrichment factors of between 32 and 189 were attained with relative standard deviations of <8%. The limits of detection for the glucocorticoids were between 0.03 and 0.17 ng/mL, whereas the limits of quantitation were between 0.09 and 0.52 ng/mL, indicating the good sensitivity of the method. The method was successfully applied to determine glucocorticoids in industrial canal water. This work also provided some insights on the potential of on-site sampling and real-time monitoring of contaminants in environmental waters.