Determination of hydroxylated benzophenone UV filters in sea water samples by dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

A new analytical method for the determination of four hydroxylated benzophenone UV filters (i.e. 2-hydroxy-4-methoxybenzophenone (HMB), 2,4-dihydroxybenzophenone (DHB), 2,2′-dihydroxy-4-methoxybenzophenone (DHMB) and 2,3,4-trihydroxybenzophenone (THB)) in sea water samples is presented. The method is based on dispersive liquid–liquid microextraction (DLLME) followed by gas chromatography–mass spectrometry (GC–MS) determination. The variables involved in the DLLME process were studied. Under optimized conditions, 1000 μL of acetone (disperser solvent) containing 60 μL of chloroform (extraction solvent) were injected into 5 mL of aqueous sample adjusted to pH 4 and containing 10% NaCl. Before injecting into the GC–MS system, the DLLME extracts were evaporated under an air stream and then reconstituted with N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA), thus allowing the target analytes to be converted into their trimethylsilyl derivatives. The best conditions for the derivatization reaction were 75 °C and 30 min. High enrichment factors for all the target analytes (ranging from 58 to 64) and good repeatability (RSD around 6%) were obtained. The limits of detection were in the range of 32–50 ng L−1, depending on the analyte. The recoveries obtained by using the proposed DLLME–GC–MS method evidenced the presence of matrix effects for some of the target analytes, and thereby the standard addition calibration method was employed. Finally, the validated method was applied to the analysis of sea water samples.