Optimisation of a solid-phase microextraction method for the determination of parabens in water samples at the low ng per litre level.

A procedure for the determination of five esters of p-hydroxybenzoic acid (parabens) in water samples is presented. Analytes (methyl, ethyl, propyl, butyl and benzyl paraben) are concentrated on a solid-phase microextraction (SPME) fibre, converted on their tert-butyldimethylsilyl derivatives and selectively determined using gas chromatography in combination with tandem mass spectrometry (GC-MS/MS). Influence of different factors on the efficiency of extraction and on-fibre derivatization steps is described in detail. For all species, the highest enrichment factors were achieved using a polyacrylate (PA) fibre exposed directly to stirred water samples, containing 150 mg/ml of sodium chloride, at room temperature. Performance of the further on-fibre derivatization reaction was also maximum at room temperature, considering a short exposition period of the SPME fibre to vapours of the silylation reagent. Under optimised conditions, the proposed method achieved quantification limits from 0.001 to 0.025 ng/ml and it was free of matrix effects; therefore, external calibration can be used as the quantification technique. From our knowledge, this work describes the first application of SPME and gas chromatography to the determination of parabens in water. The analysis of a limited number of real samples revealed the presence of parabens in raw sewage water at concentrations up to 3 ng/ml.