Supercritical fluid extraction and gas chromatographic electron capture detection method for sterol analysis of environmental water samples

Abstract

A standard additions technique was carried out by spiking standard sterol mixtures onto environmental water filtering glass fibre filters, which were then extracted by supercritical fluid extraction, derivatized into their pentafluorophenyldimethylsilyl ethers and analyzed by gas chromatography using electron capture detection. Calibration curves obtained from directly derivatized sterol standards, and also sterol standards spiked both onto blank filters and filters used to filter environmental water, were all r² > 0.99 linearity. Spiked sterol recoveries ranged from 80 to 120% with good precision, allowing application of the method to the determination of sterol levels in environmental water samples. For a sample size of 0.5 l, the limit of detection of coprostanol was estimated to be 200 ng l^–1. Water from the Prahran main drain outfall in Melbourne was analyzed and the coprostanol concentration was found to be about 400 ng l^–1, which exceeds the equivalent primary contact limit (60 ng l^–1) for this sterol in recreational waters in Australia.