Sensitive quantification of diphemanil methyl sulphate in human plasma by liquid chromatography–tandem mass spectrometry

A simple detection system with a high-performance liquid chromatography (HPLC) with positive ionisation-tandem mass spectrometry (ESI-MS/MS) for determining diphemanil methylsulphate (DMS) levels in human plasma using 4-diphemanylmethylene,1-methylpiperidine as an internal standard (I.S.), is proposed. The acquisition was performed with the multiple reactional monitoring (MRM) mode, by monitoring the transitions: m/z 278 > 262 for DMS and m/z 263 > 247 for the I.S. The method involved a simple single-step deproteinisation with acetonitrile. The analyte was chromatographed on a Zorbax® C18 reversed-phase chromatographic column by isocratic elution with 10−3 M ammonium acetate and 10−3 M hexafluorobutyric acid, adjusted to pH 7.0 with ammoniac/acetonitrile (40/60, v/v). The results were linear over the studied range (0.5–50.0 ng mL−1) and the total analysis time for each run was 10 min. The mean extraction apparent recoveries expressed at the 95% intervals of confidence were 94–104% for DMS and 92–106% for the I.S. The intra- and inter-assay precisions were 4.6–8.4% and 2.9–10.6%, respectively. The limit of quantification was 0.15 ng mL−1. The devised assay was successfully applied to the residual concentrations monitoring in infant.