Quantitative determination of the herbicide paraquat in human plasma by gas chromatographic and mass spectrometric methods

Abstract The gas chromatographic (GC) determination of the herbicide paraquat, the 1,1′-dimethyl-4,4′-dipyridyl cation in human plasma is described. In poisoning cases, plasma concentrations provide a necessary index of the severity of intoxication and a means of monitoring subsequent therapy. The methods may be extended to the specific trace analysis of paraquat in body fluids or post-mortem tissue. Reduction of fully ionised paraquat salts with sodium borohydride yields a hexahydro derivative, a diene, amenable to solvent extraction and GC. Employing 1,1′-diethyl-4,4′-dipyridyl dichloride as the internal standard, plasma concentrations of 0.1 μg/ml (± 6% S.D.) may be determined with flame ionisation detection and 0.025 μg/ml with nitrogen-selective flame ionisation. Further enhancement of specificity is achieved using selected ion monitoring mass spectrometry and the value of this technique in forensic analysis is illustrated.