Spectra interference between diquat and paraquat by second derivative spectrophotometry

A rapid and accurate method, combining solid-phase extraction and second-or der derivative spectrophotomety approaches. is developed for the simultaneo us determination of diquat (DQ) and paraquat (PQ) in blood, tissue and urin e samples. Supernatant resulting from the precipitation of protein (with tr ichloroacetic acid) in plasma and tissue or Amberlite IRA-401 resin treated urine are passed through a mini-column packed with Wakogel gel (Silica gel ). Analytes are then eluted with a non-organic solvent, 0.2 mol/l HCl solut ion containing 2 mol/l NH4Cl. UV spectrum of the eluent in 220-350 nm range provides effective screen to detect the presence of DQ and/or PQ. In the p resence of DQ or PQ alone, the analyte present is quantitated by convention al zero- or second-order derivative spectrophotometry. The calibration curv e in the 0.1-5.0 mg/l range for either analyte obeys Beer's law. When both DQ and PQ are present, their concentrations are determined by the peak ampl itudes of their respective second-derivative spectra after the addition of alkaline dithionite reagent. Interference is negligible when the DQ/PQ conc entration ratio is within the 5.0-0.2 range. Using a 2-ml of sample size, the detection limits for DQ and PQ in plasma a re 0.02 and 0.005 mg/l. The corresponding detection limits for urine sample s (10 ml sample size) are 0.004 and 0.001 mg/l. Recoveries of DQ and PQ in triplicate plasma and urine samples spiked with 0.5 mg/l of analytes are 93 and 85%. The precision of the proposed method resulting from triplicate st udy of spiked urine samples varies from 3.2 to 4.6% at 0.5 mg/l of DQ and P Q. respectively. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved .