Solid-phase extraction procedure for ethyl glucuronide in urine.

Measurement of the conjugated ethanol metabolite ethyl glucuronide (EtG) in urine is increasingly being used as a biomarker for recent alcohol consumption. Prior to quantification of EtG by mass spectrometric (MS) methods [liquid chromatography (LC)-MS or gas chromatography-MS], there is sometimes need for sample cleanup to remove interfering matrix constituents. A solid-phase extraction (SPE) procedure using a HyperSep SAX strong anion exchanger was developed for sample cleanup of urinary EtG prior to LC-MS analysis. The EtG content in a 50-100-microL urine sample was finally reconstituted in the same volume as the original aliquot. The cleaner SPE extracts, without sample dilution, allowed for improved quantification of urinary EtG in the low concentration range. The detection limit of the SPE procedure when combined with LC-MS analysis was < 0.1 mg/L EtG, and the assay imprecision < 5.5% (total CV) in the 0.5-5.0 mg/L concentration range. The absolute recovery of urinary EtG was ~80%, which was compensated for by using a deuterated analogue (EtG-d(5)) as internal standard. The urinary EtG results with SPE followed by LC-MS were highly correlated (r(2) = 0.959) with those obtained using a sensitive and selective ultra-performance LC-tandem MS method.