Measurement of urinary N-acetyl-S-(N-methylcarbamoyl)cysteine by high-performance liquid chromatography with direct ultraviolet detection

A new high-performance liquid chromatographic (HPLC) method is described for the determination of urinary N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC), the final product of the conjugation reaction between a metabolic intermediate of N,N-dimethylformamide (DMF) and glutathione. Urine samples were purified by C₁₈ solid-phase extraction and then directly analysed by HPLC with an Aminex Ion Exclusion HPX-87H column maintained at 25°C and a UV detector set at 196 nm. Under isocratic conditions (2.4 mM sulphuric acid, flow-rate=0.6 ml/min) AMCC eluted at 20.2 min. The reproducibility (C.V.%) was 1.3-2.7% (intra- and inter-assay, N=5); the accuracy was 98.0±1.7% at 10 mg/l and 101.9±1.5% at 800 mg/l (mean±SD, N=3). AMCC was measured in urine from 22 exposed subjects. A strong correlation was found between AMCC and environmental DMF [AMCC (mg/g creatinine)=3.40×DMF (mg/m³)+3.07; r=0.95], while in the urine of 20 unexposed subjects the concentration of AMCC was constantly below the detection limit of the method (0.9 mg/l in urine). The method described appears to be useful for the biological monitoring of DMF exposure.