Rapid and sensitive quantification of paraquat and diquat in human serum by liquid chromatography/time-of-flight mass spectrometry using atmospheric pressure photoionization

We developed a rapid and sensitive liquid chromatography/time-of-flight mass spectrometry (LC/TOF–MS) method using atmospheric pressure photoionization (APPI) for the determination of paraquat and diquat in human serum. Serum samples were extracted with aqueous formic acid and acetonitrile. After vortexing and centrifugation, the supernatants were filtered with ultrafiltration cartridges followed by APPI-LC/TOF–MS analysis using a hydrophilic interaction chromatography analytical column. The total amount of time required for analyzing serum samples was ≤20 min. Calibration curves using solvent standards were linear in the range of 0.0005–1.25 μg/ml. The intraday recoveries (n = 6) for paraquat and diquat added to human serum at 0.1 μg/ml were 99.0 and 91.9 %, respectively, with relative standard deviations of 5.8 and 6.5 %. The limits of detection calculated at a signal-to-noise ratio of 3 were 0.005 μg/ml for paraquat and 0.006 μg/ml for diquat. This method was applied in the analysis of four autopsy cases involving suspected paraquat intoxications. The concentration of paraquat and diquat in serum ranged from <0.005 to 72 μg/ml.