Simultaneous determination of ultraviolet filters in aqueous samples by plunger-in-needle solid-phase microextraction with graphene-based sol-gel coating as sorbent coupled with gas chromatography-mass spectrometry.

A simple, sensitive and selective method for the simultaneous determination of five ultraviolet (UV) filters: benzophenone, octyl salicylate, homosalate, 3-(4-methylbenzylidene) camphor, 2-hydroxy-4-methoxybenzophenone in aqueous samples was developed. The analytes were extracted by plunger-in-needle solid-phase microextraction with graphene as sorbent, then silylated on-fiber with N-methyl-N-(trimethylsilyl)trifluoroacetamide, and analyzed by gas chromatography-mass spectrometry. Factors affecting the performance of extraction and derivatization steps were thoroughly evaluated. For the optimization of extraction conditions, six relevant factors (parameters) were investigated, including sample pH, salt concentration, extraction time, extraction temperature, stirring speed and sampling mode. In the first stage, a two-level orthogonal array design OA(8) (2(7)) matrix was employed to study the effect of six factors. Based on the results of the first stage, three factors were selected for further optimization with a univariant approach during the second stage. Under the final optimized conditions, the method limits of detection for the five UV filters were determined to be in the range of 0.5 and 6.8 ng L(-1) (at a signal/noise ratio of 3) and the precision (% relative standard deviation, n=5) was 0.8-5.6% at a concentration level of 1 μg L(-1). The linearities for different analytes were 10-10,000 or 1-5000 ng L(-1). The coefficients of determination for the calibration curves were all greater than 0.994. Finally, the proposed method was successfully applied to the extraction and determination of the UV filters in river water samples.