Refrigerated sorptive extraction: determination of BTEX in water samples

Benzene, toluene, ethyl benzene, o-xylene, m-xylene, and p-xylene (BTEX) enrichment from aqueous samples is performed using refrigerated sorptive extraction (RSE). RSE implies the sorption of volatiles compounds into polydimethylsiloxane (approximately 0.39 mg) coated on an open stainless steel tube internally refrigerated by cold water. A metal tube is inserted into a 30-mL headspace vial through a hole at both sides of the vial. The sample inside the vial is equilibrated with stirring for 60 min at 40 degrees C. After the extraction, the analytes are desorbed with 280 microL of methanol under ultrasonic bath. BTEXs are analyzed by high resolution gas chromatography-flame ionization detection. Optimization of temperature and extraction time were carried out, as well validation in terms of linearity, precision, recuperation, limits of detection and quantification. Linearity is the range 0.999-0.998, linear range between 50 and 1000 microg/L, precision is 6.1% to 14.7% in the 0.1 microg/mL level and 3.5% to 5.6% in the 1 microg/mL level. Recovery ranged from 30% to 50%, detection limits from 1.7 to 19.6 microg/L, and quantification limits from 6.7 to 64.6 microg/L. The optimized method was applied to the analysis of water samples collected near a gas station, which was suspected of contamination by gas oil leaking from storage tanks.