Assessment of ethyl sulphate in hair as a marker for alcohol consumption using liquid chromatography-tandem mass spectrometry

Ethyl glucuronide (EtG) and ethyl sulphate (EtS) are 2 non-oxidative and direct metabolites of ethanol. EtG is known to accumulate in hair and has proved to be a reliable biomarker for detection of chronic alcohol consumption. EtS has been analysed in blood and urine but has never been reported in hair. This article presents the first analytical assay based on liquid chromatography coupled to tandem mass spectrometry for the quantification of EtS in hair. Sample preparation, chromatographic, and mass spectrometric parameters, such as solid-phase extraction, column type, and transitions were optimised. The method was validated according to the guidelines of the European Medicine Agency, fulfilling the requirements for limit of quantification (LOQ), linearity, accuracy, precision, carry-over, matrix effects, and recovery. Linearity ranged from 5 to 500 pg mg(-1) and the LOQ was achieved at 5 pg mg(-1). The novel method was successfully applied to hair samples (n=40) from patients treated for alcohol use disorders. EtS concentrations in hair ranged from 24 to 1776 pg mg(-1), while EtG concentrations in hair ranged from 1 to 1149 pg mg(-1). Hair concentrations of EtS and EtG were compared to assess the relationship between both biomarkers. There was a significant and positive correlation between EtS and EtG in hair, suggesting that EtS can be used as a biomarker for alcohol consumption. Relatively high basal EtS levels were observed in alcohol-abstinent persons, comparable to what has been reported for EtG. The developed analytical procedure offers an alternative method to prove alcohol consumption using hair analysis.