Organophosphorus pesticide degradation product in vitro metabolic stability and time-course uptake and elimination in rats following oral and intravenous dosing

Levels of urinary dialkylphosphates (DAPs) are currently used as a biomarker of human exposure to organophosphorus insecticides (OPs). It is known that OPs degrade on food commodities to DAPs at levels that approach or exceed those of the parent OP. However, little has been reported on the extent of DAP absorption, distribution, metabolism and excretion. The metabolic stability of O,O-dimethylphosphate (DMP) was assessed using pooled human and rat hepatic microsomes. Time-course samples were collected over 2 h and analyzed by LC-MS/MS. It was found that DMP was not metabolized by rat or pooled human hepatic microsomes. Male Sprague-Dawley rats were administered DMP at 20 mg kg(-1) via oral gavage and i.v. injection. Time-course plasma and urine samples were collected and analyzed by LC-MS/MS. DMP oral bioavailability was found to be 107 ± 39% and the amount of orally administered dose recovered in the urine was 30 ± 9.9% by 48 h. The in vitro metabolic stability, high bioavailability and extent of DMP urinary excretion following oral exposure in a rat model suggests that measurement of DMP as a biomarker of OP exposure may lead to overestimation of human exposure.

A Gas Chromatograph/Resonant Electron Capture-TOF Mass Spectrometer for Four Dimensions of Negative Ion Analytical Information

A prototype gas chromatograph (GC) electron monochromator (EM) reflectron time-of-flight (TOF) mass spectrometer has been constructed and demonstrated to simultaneously record four-dimensional resonant electron capture (REC) mass spectra (m/z, ion-intensity, electron-energy, and retention time) of electron-capturing compounds in real time. Specifically, complete REC mass spectra of all of the components in a mixture of perfluorocarboxylic acids and in a sample of pentafluorobenzyl alcohol were recorded in the GC mode. For each compound, the data enable one to distinguish different electronic states of the molecular ion and different possible decomposition pathways for each state. This new instrument can be used to obtain analytical information unrecognizable by any other mass spectrometric technique from the isomeric species of a variety of electron-capturing structures.