Analysis for paraquat by second- and fourth-derivative spectroscopy.

We describe simple, precise methods, based on second and fourth-derivative spectroscopy, of analysis for paraquat in serum, plasma, or dialysis fluid. Plasma paraquat, after ion-pair extraction and dithionite reduction, yields a sharp, stable absorption peak at 396 nm. Derivative spectroscopy confers enhanced sensitivity (detection limit, 5 microgram/L) and improved rejection of spectroscopic interference by diquat, hemolysis, bilirubin, or lipemia. Derivative peak amplitudes are linearly related to paraquat dichloride concentration from 10 to 1000 microgram/L in plasma, and the methods are precise (CV 2.7-5.2% for 50 microgram/L concentration) and accurate. Results of derivative assays for 18 cases of paraquat poisoning correlate well with those by radioimmunoassay (r = 0.999). Derivative spectroscopy enables monitoring of paraquat concentrations in the plasma of poisoned patients during treatment by hemoperfusion or hemodialysis. A rapid assay developed for dialysis fluid (detection limit, 2 microgram/L) permits the efficacy of hemodialysis to be routinely assessed.