Determination of Herbicide Difenzoquat Methyl Sulfate in Citruses and Baby Juices by Kinetic-Spectrophotometric Method and HPLC Method

The purpose of this paper is to present a new kinetic-spectrophotometric method which involve inexpensive equipment and which can be applied by all analyst who have to determine difenzoquate methyl sulfate (DFQ) residues in citruses and baby juices. The method is based on the inhibited effect of DFQ on the oxidation of sulfanile acid (SA) by hydrogen peroxide in phosphate buffer in presence Cu(II) ion. The reaction was monitored spectrophotometrically by measuring the increase in absorbance of the reaction product at 370 nm. The proposed inhibited method permits determination of DFQ over the range 0.36 to 1.80 mu g/mLand 1.80 to 7.20 mu g/mL, with quantification limit of 0.184 mu g/mL. The relative standard deviations are 0.73-2.90% for the concentration interval of DFQ 1.80-0.36 mu g/mL. The method was successfully applied to determination of DFQ residues in citruses and baby juices. The HPLC method is used to verify the results. The results obtained for the same samples by the two methods are quite comparable.