Determination of metabolites of di(2-ethylhexyl) terephthalate (DEHTP) in human urine by HPLC-MS/MS with on-line clean-up.

Abstract

Di(2-ethylhexyl) terephthalate (DEHTP) is used as a substitute for ortho-phthalate based plasticizers like di(2-ethylhexyl) phthalate (DEHP) which are discussed and regulated due to their reproductive toxicity. We developed a fast and rugged method to quantify side chain oxidized monoesters of DEHTP in human urine, namely 5OH-MEHTP, 5oxo-MEHTP, 2cx-MMHTP and 5cx-MEPTP. Sample preparation was kept simple with enzymatic deconjugation and a two column assembly for on-line sample clean up. Metabolites were identified with authentic standards and quantified via isotope dilution LC-MS/MS. The limit of quantification was 0.2μg/L for 5cx-MEPTP and 5oxo-MEHTP, 0.3μg/L for 5OH-MEHTP and 0.4μg/L for 2cx-MMHTP. Accuracy (relative recovery: 95.8-111%) and precision (relative standard deviation: <7%) were highly acceptable. In a pilot biomonitoring study with 34 volunteers (aged 25-61 (median 42), 20 female and 14 male) not known to be occupationally exposed to DEHTP, we could detect 5cx-MEPTP above the limit of quantification in 94% of the samples (median: 0.9μg/L, maximum: 38.7μg/L). The other metabolites investigated were detected at a lower rate and at lower concentration levels (5oxo-MEHTP: 21%, maximum: 1.8μg/L; 5OH-MEHTP: 18%, maximum: 3.4μg/L; 2cx-MMHTP: 9%, maximum: 0.9μg/L). All target analytes can be regarded as promising and specific urinary biomarkers for DEHTP exposure. With this method we provide a basis for quantitatively investigating the human metabolism of DEHTP and for performing exposure and risk assessments in the general population and the working environment.