A fully validated method for the quantification of ethyl glucuronide and ethyl sulphate in urine by UPLC–ESI-MS/MS applied in a prospective alcohol self-monitoring study

Abstract

A method for the quantification of ethyl glucuronide (EtG) and ethyl sulphate (EtS) in human urine is developed and fully validated according to international guidelines. Protein precipitation is used as sample preparation. During the development of the method on an UPLC-ESI-MS/MS system using a CSH C18 column, special attention was paid to reduce matrix effects to improve assay sensitivity and to improve detection of the second transition for EtS for specificity purposes. The method was linear from 0.1 to 10μg/mL for both analytes. Ion suppression less than 24% (RSD<15%) was observed for EtG and no significant matrix effect was measured for EtS. The recovery was around 80% (RSD<14%) for both compounds. This method provides good precision (RSDr and RSDt<10%) and bias (<15%) for internal and external quality control samples. The reproducibility of the method was demonstrated by the successful participation to proficiency tests (z-score<0.86). This method was finally used to analyze urine samples obtained from twenty-seven volunteers whose alcohol consumption during the 5 days before sampling was monitored. Concentrations between 0.5 and 101.9μg/mL (mean 10.9, median 1.4) for EtG and between 0.1 and 37.9μg/mL (mean 3.6, median 0.3) for EtS were detected in urine samples of volunteers who declared having consumed alcohol the day before the sampling. EtG and EtS concentrations in urine were highly correlated (r=0.996, p<0.001). A moderate correlation between the number of drinks the day before sampling and the concentration of EtG (r=0.448, p<0.02) or EtS (r=0.406, p<0.04) was observed. Using a cut-off value at 0.1μg/mL for EtG and EtS, this method is able to detect social alcohol consumption approximately 24h after the intake, without showing any false positive result.