Double-wavelength spectrophotometric determination of micro iodine in soil

A new method for the determination of micro iodine by double-wavelength spectrophotometry with 514 nm as the measureing wavelength and 548 nm as the reference wavelength was developed.In the presence of PVA-124,dissociation of the ion-association complex of Ag+-phen-eosin Y was accelerated by the deposition reaction between I-and Ag+ in acetate buffer solution at pH 4.5,resulting in a positive absorption peak at 514 nm and a negative absorption peak at 548 nm.The optimal conditions of measurements of iodine including acidity,reagent dosage,stabilizer,reagent adding sequence,temperature and time were studied.The metal ions,i.e.,Co2+,Fe3+,Zn2+ could be separated by 732-type cation exchange resin,and the interferences of oxidative ions could be eliminated by adding ascorbic acid.The linear range of the determination of iodine was 0.05-0.4 μg/mL.The apparent molar absorptivity was 1.18×105 L·mol-1·cm-1,and the detection limit was 26.2 μg/L.The method was applied to determine iodine in seashore salines and brown soil samples from Lianyungang city.The results showed good agreement with those obtained by ion chromatography(IC).RSDs were 1.6 % and 1.9 %(n = 5),respectively.Recoveries were found to be 97 %-99 %.