Quantitative Analysis of EtG and EtS in Urine Using FASt® ETG and LC-MS-MS

Introduction

Ethyl glucuronide (EtG) and ethyl sulfate (EtS) are conjugated ethanol metabolites formed in low amounts in the body following alcohol consumption. Compared with ethanol, EtG and EtS are excreted in urine for a prolonged time. Published literature indicates that EtG may be detectable for up to 80 hours after alcohol ingestion, while EtS is generally detectable for up to 24 hours after use, making them both valuable as sensitive alcohol biomarkers. The detection of these metabolites has proven advantageous for zero tolerance treatment programs and abstinence enforcement where information regarding recent alcohol consumption is required. The cutoff level for EtG confirmation is typically 500 ng/mL or higher; the EtS confirmation cut-off level is generally set at 100 ng/mL.

When analyzing chemical residues in a complex biological matrix, such as urine, a sample pre-treatment step is generally required to eliminate non-desirable matrix components and/or concentrate the analyte(s) of interest. However, due to the highly polar nature of EtG and EtS (log P of 1.51 and 0.62, respectively), many labs turn away from traditional sample preparation procedures and instead use a dilute-and-shoot or simple filtration approach. These techniques do not adequately remove interferences from the sample and significant matrix suppression is commonly experienced during instrumental analysis. This is further complicated by the lack of retention of EtG/EtS on a traditional reversed phase HPLC column.