Quantification of biomarkers of environmental exposure to di(isononyl)cyclohexane-1,2-dicarboxylate (DINCH) in urine via HPLC–MS/MS

Di(isononyl)cyclohexane-1,2-dicarboxylate (DINCH) is a major substitute for some high molecular weight phthalates that adversely affect reproductive function. Like for the phthalates a broad exposure of the population has to be expected. We postulated the DINCH monoester (MINCH) and secondary oxidized metabolites (OH-MINCH, cx-MINCH and oxo-MINCH) as human metabolites and possible biomarkers of DINCH exposure. We developed an on-line HPLC–MS/MS method for their determination in human urine. Identification was performed with authentic standard substances and quantification via isotope dilution. The analytical method is highly selective and sensitive with limits of quantification (LOQ) between 0.05 μg/l and 0.1 μg/l. In a pilot study with 22 volunteers from the general German population oxidized DINCH metabolites were found in above 80% of the samples. OH-MINCH was most abundant (mean 0.71 μg/l; maximum 3.69 μg/l) followed by cx-MINCH (0.61 μg/l; 2.82 μg/l) and oxo-MINCH (0.33 μg/l; 1.05 μg/l). All three oxidized metabolites correlated strongly among each other (ρ ≥ 0.76). MINCH was detected in one sample only and has to be regarded a weak marker of exposure. With this analytical method we are able to perform human metabolism studies to provide metabolic conversion factors and to investigate the extent of DINCH exposure in the general population.