Determination of human urinary metabolites of the plasticizer di(2-ethylhexyl) adipate (DEHA) by online-SPE-HPLC-MS/MS

Di(2-ethylhexyl) adipate (DEHA) is a plasticizer and phthalate substitute used in various consumer products. Relevant population exposures have to be assumed. In this study we describe the determination of three specific side chain-oxidized monoester metabolites of DEHA, mono-2-ethyl-5-hydroxyhexyl adipate (5OH-MEHA), mono-2-ethyl-5-oxohexyl adipate (5oxo-MEHA), and mono-5-carboxy-2-ethylpentyl adipate (5cx-MEPA) in human urine as potential biomarkers of DEHA exposure. After enzymatic hydrolysis, urine samples were analyzed by online turbulent flow chromatography for matrix depletion and analyte enrichment coupled to liquid chromatography-electrospray ionization-triple quadrupole-tandem mass spectrometry (online-SPE-LC-MS/MS). For quantification stable isotope dilution was applied with limits of quantification of 0.05 μg/L for 5cx-MEPA and 5OH-MEHA, and 0.1 μg/L for 5oxo-MEHA. Method accuracies (relative recoveries) were between 92 and 109%, and relative standard deviations