Simultaneous Determination of Zinc and Lead in Food by the Improved Multi-wavelength K-Factor-Spectrophotometry

An improved method of multiwavelength K-Factor-spectrophotometric determination of zinc and lead in food,using 5-Br-PADAP as chromogenic reagent and Trion X-100 as solubilizing agent,was reported in this paper.Error due to the absorption of 5-Br-PADAP in the measuring wavelength region was eliminated by using a reference solution of the blank solution without addition of chromogenic reagent.The color reaction for both zinc and lead with 5-Br-PADAP was carried out in an ammoniacal buffer solution of pH 9.2.In the determination of zinc,558 nm was chosen as the measuring wavelength,and 572 nm,446 nm were chosen as the reference wavelengths,while in the determination of lead,the measuring wavelength and reference wavelengths chosen were 572 nm and 558 nm,446 nm respectively.Linearity for both elements were in the range of 1.0 to 20.0 μg per 25 mL of testing solution.Zinc and lead in samples of gourmet powder and preserved egg were determined by the proposed method giving results in consistency with the results obtained by AAS.Based on these samples,standard solutions of Zn2+ and Pb2+ were added and tests for recovery were performed,results obtained were in the ranges of 96.5%-104.2% for Zn and 95.0%-103.7% for Pb.