Direct Determination of 1-Naphthol in Human Urine by Coupled-Column Liquid Chromatography with Fluorescence Detection

Abstract

A rapid and automated method based on coupled-column liquid chromatography (LC-LC) with fluorescence detection has been developed for the determination of 1-naphtol in human urine. Urine samples were hydrolyzed with sulfatase and a 100 μL aliquot was directly injected in the LC-LC system, using as first separation column a Kromasil C18 10 μm 30 × 4 mm. The fraction containing the analyte was transferred on-line to the second analytical column ABZ+ 5 μm 150 × 4 mm, which was connected to the fluorescence detector. The clean-up performed by the coupled-column system gave the necessary selectivity and avoids additional clean-up steps. The method was linear in the range 10–500 ng mL−1 (correlation coefficient of 0.9999). Accuracy and precision were evaluated by means of recovery experiments from different fortified urine samples (25 and 250 ng mL−1), obtaining coefficients of variation lower than 5% and recoveries between 91 and 102% in all cases. The method proposed allows the determination of 1-naphthol at a concentration level as low as 10 ng mL−1, without any preconcentration step. The applicability of the proposed method has been confirmed by analyzing different urine samples from a farmer exposed to carbaryl. Concentrations of 1-naphthol, the main metabolite of carbaryl, between 60 and 80 ng mL−1 were found in urine samples obtained during the application period of carbaryl in the field. 72 h after finishing the application, 1-naphtol was not detected in urine.