This study describes the development of a novel and sensitive UPLC-MS/MS method for simultaneous determination of diethyl phthalate (DEP) and its major metabolite, monoethyl phthalate (MEP), in rat plasma, urine, and 11 different tissues collected from a toxicokinetic study. Analytes were separated using 0.1% (v/v) aqueous formic acid and acetonitrile containing 0.1% (v/v) formic acid as a mobile phase by gradient elution at a flow rate of 0.25 mL/min with a KINETEX core-shell C18 column (50 × 2.1 mm, 1.7 μm). Quantitation was performed on a triple quadrupole mass spectrometer employing electrospray ionization technique operated in multiple reaction monitoring. The assay achieved lower limit of quantification for 0.04 ng/mL of DEP and 0.1 ng/mL of MEP in plasma, urine, and all tissues. The disposition of DEP was characterized by short half-life (1.30-1.34 h) and a high clearance (11.76 ± 0.08 L/h/kg). It was rapidly metabolized to MEP. Its levels consistently exceeded DEP levels. The tissue distribution of DEP and MEP of liver, kidney, gastro-intestinal tract, spleen, testis, lung, brain, muscle, thymus, heart, and adipose was determined at 24 h after drug administration. For DEP, the tissue to plasma partition coefficient was the highest in the kidney (16.72), followed by that in the liver (10.04), spleen (1.35), and adipose (1.18). For MEP, the tissue to plasma partition coefficient was the highest in the liver (2.18). It was less than unity for all other tissues. The developed analytical method satisfied the criteria of international guidance. It could be successfully applied to toxicokinetic studies of DEP after oral and intravenous administration of DEP to rats. In addition, findings of this study may be useful to evaluate exposure and toxic potential of DEP and its metabolite in risk assessment.
Keywords: Diethyl phthalate; Monoethyl phthalate; Tissue distribution; Toxicokinetic; UPLC-MS/MS.
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