Comprehensive monitoring of specific metabolites of tri-(2-ethylhexyl) trimellitate (TEHTM) in urine by column-switching liquid chromatography-tandem mass spectrometry

Tri-(2-ethylhexyl) trimellitate (TOTM or TEHTM) is a substitute for the plasticizer di-(2-ethylhexyl) phthalate (DEHP). Here, a fast and robust HPLC method is presented for the first time enabling the simultaneous quantification of several TEHTM metabolites in urine. These are the three TEHTM monoester isomers 1-mono-(2-ethylhexyl) trimellitate (1-MEHTM), 2-mono-(2-ethylhexyl) trimellitate (2-MEHTM), and 4-mono-(2-ethylhexyl) trimellitate (4-MEHTM) as well as several selected side chain oxidized monoesters of TEHTM, namely, 1-mono-(2-ethyl-5-hydroxyhexyl) trimellitate (5OH-1-MEHTM), 2-mono-(2-ethyl-5-hydroxyhexyl) trimellitate (5OH-2-MEHTM), 1-mono-(2-ethyl-5-oxohexyl) trimellitate (5oxo-1-MEHTM), 2-mono-(2-ethyl-5-oxohexyl) trimellitate (5oxo-2-MEHTM), 1-mono-(2-ethyl-5-carboxypentyl) trimellitate (5cx-1-MEPTM), 2-mono-(2-ethyl-5-carboxypentyl) trimellitate (5cx-2-MEPTM), 2-mono-(2-carboxymethylhexyl) trimellitate (2cx-2-MMHTM), and 1-mono-(2-carboxymethylhexyl) trimellitate (2cx-1-MMHTM). The method is characterized by a short sample preparation, for which the urine samples are enzymatically hydrolyzed and cleaned up by an online column arrangement. Separation of the analytes is enabled using liquid chromatography coupled with tandem mass spectrometry. Thus, in less than 30 min, 11 postulated metabolites of TEHTM can be selectively and sensitively quantified. The method is distinguished by its wide linear working range of up to 1800 μg/L with detection limits ranging from 0.3 μg/L (for 5oxo-1-MEHTM) to 1.5 μg/L (for 1-MEHTM). Precision and repeatability of the method were proven with determined relative standard deviations between 2.5 and 11.3%. The selection of the analytes of this method was based on a pilot study, by which several potential TEHTM metabolites were investigated in human urine of an orally exposed volunteer. Thus, the here presented method is a perfect tool for human biomonitoring of TEHTM exposure.