Simultaneous determination of bentazone and its metabolites in postmortem whole blood using liquid chromatography-tandem mass spectrometry

•A LC-MS/MS method was developed to determine bentazone concentrations in blood specimens.•Target analytes were bentazone and its two hydroxylated metabolites.•The solid phase extraction of bentazone and its metabolites from blood was used.•The method was selective and sensitive for each analyte.•Fatal cases of bentazone poisoning by oral ingestion were applied.

A liquid chromatography-tandem mass spectrometry method with solid-phase extraction (SPE) was developed and validated for the detection and quantitation of bentazone and its two hydroxylated metabolites, 6-hydroxybentazone and 8-hydroxybentazone, in postmortem blood. Sample cleanup was performed using a hydrophilic-lipophilic balanced (HLB) SPE cartridge and then separated on a C18 LC column using a gradient elution of 0.1% formic acid in distilled water and 0.1% formic acid in methanol. The identification of bentazone and its hydroxylated metabolites was performed using tandem mass spectrometry with electrospray ionization in negative ion mode with selective reaction monitoring. The retention times of bentazone, 6-hydroxybentazone, 8-hydroxybentazone, and 2-methyl-4-chlorophenoxyacetic acid (MCPA, internal standard) appeared separately in the chromatogram. The matrix effect, recovery, and process efficiency of bentazone were 75.3%, 103.6% and 77.9%, respectively. In addition, good accuracy (88.2-110.5%), precision (0.5-7.5%, bias), and linearity (5-500 ng/mL) were obtained with this method. The limit of detection (LOD) of bentazone, 6-hydroxybentazone, and 8-hydroxybentazone were 0.05, 0.5, and 0.5 ng/mL, respectively. The method developed herein was applied to authentic samples from three fatal cases from 2016 for the determination of the corresponding bentazone and its metabolites levels. The concentration ranges of bentazone, 6-hydroxybentazone, and 8-hydroxybentazone in the heart blood from the three victims were 46.0-91.8, 4.2-6.2, and 0.2-0.6 μg/mL, respectively.