Determination of ethyl sulfate in human serum and urine by capillary zone electrophoresis

The use of capillary zone electrophoresis (CZE) with indirect absorbance detection for the analysis of ethyl sulfate (EtS) in serum and urine was investigated. EtS is a direct metabolite of ethanol employed as marker for recent alcohol consumption. Fused-silica capillaries of 60 cm total length were either coated with cetyltrimethylammonium bromide (CTAB, 50 μm I.D. capillary) or poly(diallyldimethylammonium chloride) (PDADMAC, 100 μm I.D. capillary) to allow CZE analyses to be performed with reversed polarity. At pH 2.2 with a maleic acid/phthalic acid background electrolyte, both approaches provided reliable EtS serum levels down to 0.2 mg L−1 (1.6 μM) for the analysis of solid-phase extracts that were prepared after chloride precipitation. Analysis of urines diluted to a conductivity of 5 S m−1 and analyzed in the two capillary formats resulted in limits of quantification (LOQs) of 2 and 1 mg L−1, respectively. With urines adjusted to 10 S m−1 via dilution or condensation, an LOQ of 0.6 mg L−1 (4.8 μM) was obtained in the CTAB coated capillary whereas in the PDADMAC-coated capillary of equal length not all matrix components were resolved from EtS. The developed assays are robust and suitable to monitor EtS in samples of individuals who consumed as little as one standard drink of an alcoholic beverage containing about 14 g of ethanol.