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.
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