Spectra Interference between Diquat and Paraquat by Second Derivative Spectrophotometry

Abstract

A rapid and accurate method, combining solid-phase extraction and second- order derivative spectrophotometry approaches, is developed for the simultaneous determination of diquat (DQ) and paraquat (PQ) in blood, tissue and urine samples. Supernatant resulting from the precipitation of protein (with tricholoroacetic acid) in plasma and tissue or Amberlite IRA -401 resin treated urine are passed through a mini-column packed with Wakogel gel (Silica gel). Analystes are then eluted wiht a non-organic solvent, 0.2 mol/L HCl solution 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 presence of DQ or PQ alone , the analyte present is quantitated by conventional zero- or second-order derivative spectrophotometry. The calibration curve in the 0.1-5.0 mg/L range for either analyte obeys Beer's law. When both DQ and PQ are present, their concentratons are determined by the peak amplitudes of their respective second-derivative spectra after the addition of alkaline dithionite reagent. Interference is neglilgible when the DQ/PQ concentration ratio is whithin the 5.0-0.2 range. Using a 2-mL of sample size, the detection lilmits for DQ and PQ in plasma are 0.02 and 0.005 mg/L. The corresponding detection limits for urine samples( 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 study of spiked urine samples varies from 3.2 to 4.6% at 0.5 mg/L of DQ and PQ, respectively.