Toxicokinetic Characterization of Isopropyl Glycidyl Ether in Rat by a Validated LC-APCI-MS/MS Method Using In-Source Derivatization

Abstract

Isopropyl glycidyl ether (IPGE) is a member of the large glycidyl ether family frequently used as a reactive diluent during the epoxy resin manufacturing process. Although the toxicity induced by this type of chemical has been investigated in many studies of different aspects (acute, subchronic, genotoxic, reproduction, etc.), there is still little known about their toxicokinetics. To gain information about the attainable systemic concentration, a liquid chromatography─tandem mass spectrometry (LC–MS/MS) method was developed and validated for the quantification of IPGE in rat plasma using its structural analogue tert-butyl glycidyl ether as the internal standard. Two types of atmospheric pressure ionization techniques have been utilized; however, the protonated molecule ion could not be observed in either ionization mode. First, the ammonium adduct form was used for fragmentation, albeit this multiple-reaction monitoring transition proved to be not sensitive enough for real study sample analysis. In order to achieve the desired sensitivity, the Meerwein reaction was applied as an in-source derivatization tool to generate a product by using the ethylnitrilium ion formed from the eluent acetonitrile. This gas-phase reaction enabled us to build up a method with a substantial sensitivity increase (LLOQ of 0.01 μg/mL) compared to that obtained with the ammonium adduct. After method validation, real study samples from a single-dose oral toxicity study were analyzed to evaluate the blood plasma concentration of IPGE at three dose levels. Dose-dependent superproportional systemic exposure was observed in the studied dose range (1000–2000 mg/kg). Additionally, seven metabolites of IPGE were tentatively identified in rat plasma: 3-isopropoxy-2-hydroxy-1-propanol (M1), sulfate-conjugate of IPGE (M3), glucuronide-conjugate of IPGE (M4), 3-isopropoxy-2-hydroxypropionic acid (M5), O-isopropyl-N-acetylserine (M6), O-(2-hydroxy-isopropyl)-N-acetylserine (M7), and glutathione-conjugate of IPGE (M11). Present work may pave the way to other methods that are able to quantify compounds similar to IPGE even in human plasma, which could provide valuable information to assist exposure assessment and biomonitoring in occupational health and safety studies.