Ultrasound-assisted and disposable pipette extraction for the determination of faecal contaminants in sediment samples by GC-MS

Abstract

ABSTRACT Given the amount of untreated sewage released into the environment and possible consequences, new methodologies are required for the detection and quantification of potential pollutants found in sediment samples, including faecal contamination. Solid matrix extraction methodologies (e.g. Soxhlet extraction) are generally laborious and require the use of large amounts of solvents, which is inconsistent with the principles of green chemistry. In this study,a simple, robust and efficient analytical method for the determination of faecal sterols in sediment samples using ultrasound-assisted extraction (UAE) followed by pre-concentration with disposable pipette extraction (DPX) was developed. Multivariate experimental designs were used for the optimisation of the extraction parameters for the UAE and DPX procedures. The separation and detection of the analytes were conducted by GC-MS. Dichloromethane was used as the extraction solvent in the UAE. The DPX procedure was conducted applying 5 cycles of extraction with 700 µL of sample (10 s each) and 2 cycles of desorption with 200 µL of solvent (20 s each). The optimised desorption solvent was a mixture composed of ethyl acetate:acetonitrile (60:40 v/v). The limits of detection were 7.6 µg kg−1 for cholesterol and 75 µg kg−1 for cholestanol, coprostanol and stigmasterol and the limits of quantification were 25 µg kg−1 for cholesterol and 250 µg kg−1 for the other analytes. Relative recovery was evaluated for 3 levels of concentration and the results ranged from 78% to 114%. The precision was evaluated through intra-day (n = 3) and inter-day (n = 9) tests, and the ranges observed were 0.5–10%and 2–16%, respectively. The results demonstrate that this effective and fast method shows potential for the determination of faecal contaminants in sediments.