A UPLC-MS/MS method for the determination of 2-nitro-1,3-propanediol, a metabolite of Bronopol, in human urine

Bronopol is a preservative with applications in various industrial fields; thus, the general population may be exposed to this substance. For the development of an analytical method for human biomonitoring (HBM) in urine, 2-nitro-1,3-propanediol was postulated as a suitable biomarker according to findings in animal studies. The herein described UPLC-MS/MS method enables the quantification of 2-nitro-1,3-propanediol in a concentration range from 0.5 μg l^-1 (LOQ) to 5000 μg l^-1. The sample preparation is based on a liquid-liquid extraction with ethyl acetate. Analyte losses are compensated by the authentic, isotope-labelled internal standard 2-nitro-1,3-propanediol-¹³C₃. The method fulfils all reliability criteria: intra- and interday coefficients of variation (CVs) were determined in spiked pooled urine samples at 1, 10 and 100 μg l^-1 and did not exceed 5%. The corresponding accuracies were between 104 and 105%. In individual urine samples (robustness, n = 10) spiked at the same levels, CVs were <8% and accuracies ranged between 98 and 104%. Applying different hydrolysis protocols, we could rule out any phase II metabolites of 2-nitro-1,3-propanediol from being excreted in urine. Thanks to samples from a human metabolism study involving oral intake of Bronopol, we were able to confirm the postulated metabolite. In representative specimens, the analyte could be quantified in large amounts, demonstrating the applicability of the method both for high concentrations in metabolism studies and occupational medicine, and at lower levels, for example, in field studies to assess the burden of the general population.