Determination of methyl paraoxon in dog plasma by reversed-phase high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of methyl paraoxon in plasma has been developed. Disodium EDTA and aluminon are used to inhibit hydrolysis of methyl paraoxon in plasma. Methyl paraoxon and the internal standard fenitrooxon are extracted from plasma into methylene chloride. Chromatography is performed on a reversed-phase C18 column, connected with a fixed-wavelength ultraviolet detector at 280 nm; the compounds are eluted in about 5 min with tetrahydrofuran-acetonitrile-0.01 M sodium phosphate buffer, pH 7.4 (12:25:63, v/v/v). Concentrations down to 5 ng/ml methyl paraoxon in plasma can be determined with good precision and accuracy. The method was applied to plasma samples from dogs after intravenous administration.