Sensitive determination of salicylate and benzophenone type UV filters in water samples using solid-phase microextraction, derivatization and gas chromatography tandem mass spectrometry

A sensitive procedure for the determination of three UV filters: ethylhexyl salicylate (EHS), 3,3,5-trimethylcyclohexyl salicylate (Homosalate, HMS), 2-hydroxy-4-methoxybenzophenone (BP-3) and two related hydroxylated benzophenones (2,4-dihydroxybenzophenone, BP-1 and 2,2′-dihydroxy-4-methoxybenzophenone, BP-8) in water samples is presented. Analytes were first concentrated on the coating of a solid-phase microextraction (SPME) fibre, on-fibre silylated and then determined using gas chromatography combined with tandem mass spectrometry (GC-MS/MS). Factors affecting the performance of extraction and derivatization steps are thoroughly evaluated and their effects on the yield of the sample preparation discussed. Under final working conditions, a PDMS-DVB coated SPME fibre was exposed directly to 10 mL of water, adjusted at pH 3, for 30 min. After that, the fibre was placed in the headspace (HS) of a 1.5 mL vial containing 20 μL of N-methyl-N-(trimethylsilyl)-trifluoroacetamide (MSTFA). On-fibre silylation of hydroxyl groups contained in the structure of target compounds was performed at 45 °C for 10 min. The whole sample preparation process was completed in 40 min, providing limits of quantification from 0.5 to 10 ng L⁻¹ and acceptable precision (RSDs under 13%) for samples spiked at different concentrations. All compounds could be accurately determined in river and treated wastewater (relative recoveries from 89 to 115%) using standards in ultrapure water, whereas standard addition is recommended to quantify their levels in untreated wastewater. Analysis of wastewater revealed the systematic presence of BP-3 and BP-1 in raw samples with maximum concentrations close to 500 and 250 ng L⁻¹, respectively.