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

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 of 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 microgram/ml (+/- 6% S.D.) may be determined with flame ionisation detection and 0.025 microgram/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.