Determination of metabolites of the UV filter 2-ethylhexyl salicylate in human urine by online-SPE-LC-MS/MS.

The UV filter 2‑ethylhexyl salicylate (EHS) is widely used in sunscreens and other personal care products (PCP). EHS has been detected in a variety of environmental matrices. However, data on the internal EHS exposure in humans is not available, due to the lack of exposure biomarkers and analytical methods for their determination. Here, we report a method for the determination of three oxidative EHS metabolites in human urine: 2‑ethyl‑5‑hydroxyhexyl 2‑hydroxybenzoate (5OH-EHS), 2‑ethyl‑5‑oxohexyl 2‑hydroxybenzoate (5oxo-EHS), and 5‑(((2‑hydroxybenzoyl)oxy)methyl)heptanoic acid (5cx-EPS). Urine samples are incubated with β‑glucuronidase and analyzed by liquid chromatography-electrospray ionization-triple quadrupole-tandem mass spectrometry, coupled with online sample clean-up and analyte enrichment using turbulent flow chromatography (online-SPE-LC-MS/MS). Quantification is performed by stable isotope dilution analysis, using deuterium-labeled standards of each of the three metabolites. The described method is precise (coefficient of variation <5% within-series and interday), accurate (mean relative recoveries between 96% and 105%), and sensitive, with limits of quantification (LOQ) of 0.01 μg/L (5cx-EPS), 0.05 μg/L (5OH-EHS), and 0.15 μg/L (5oxo-EHS). After dermal application of an EHS containing sunscreen to a human volunteer, we were able to quantify all three metabolites in urine samples collected post application, showing clear elimination kinetics. In spot urine samples from the general population (n = 35) we were able to quantify EHS biomarkers in 91% of all samples, with highest concentrations in individuals (n = 11) who stated use of PCPs containing UV filters within 5 days prior to sampling. We will apply the method for investigating human EHS metabolism and in future human biomonitoring studies for EHS exposure and risk assessment.