A solid-phase extraction liquid chromatography-tandem mass spectrometry method for the percutaneous absorption assessment of 3-(4′-methylbenzylidene)camphor via human urine analysis

Abstract

The UV filter 3-(4′-methylbenzylidene)camphor (MBC) is a common ingredient in sunscreen cosmetic products. However, different in vitro and in vivo studies suggest that MBC can cause endocrine disrupting effects. This report focuses on the development of an analytical method based on solid-phase extraction (SPE) prior to liquid chromatography tandem mass spectrometry (LC-MS/MS) for the determination of MBC and its main phase I metabolite, named 3-(4′-carboxybenzylidene)camphor (CBC), in urine from users of sunscreen cosmetic products containing MBC. The formation of phase II metabolites (i.e., glucuronide and sulphate conjugates) was also considered by carrying out an enzymatic hydrolysis of the urine samples. The standard addition calibration method was used to quantify the target analytes in order to correct the matrix effects observed. In this way, statistically accurate results were obtained when the developed SPE-LC-MS/MS method was applied to the analysis of fortified analytes-free urine samples. The limits of detection were 6 ± 2 ng mL⁻¹ for MBC and 6 ± 1 ng mL⁻¹ for CBC, and the intra- and inter-day variability of the method, expressed as relative standard deviation, were in the range of 1.3–2.0% and 4.5–7.7%, respectively, depending on the analyte. The analytical method was satisfactorily applied to the analysis of real urine samples from a volunteer that was subjected to repeated applications of a sunscreen cosmetic containing MBC, showing that the major contribution to the excretion of MBC corresponded to the glucuronide conjugated species of CBC. Furthermore, the second main phase I metabolite of MBC, named 3-(4′-carboxybenzylidene)hydroxycamphor (CBC-OH), which also predominates in its glucuronide conjugate species in urine samples, was identified and detected.