Spectrophotometric determination of trace cadmium with cadmium(II)-potassium iodide-acridine orange association system

A new spectrophotometric method was developed for the determination of trace cadmium.The method was based on the reaction of Cd2+ with excess KI and acridine orange(AO),which forms a stable ion-association complex 2 in NaAc-HAc buffer solution at pH 3.6,resulting in a great enhancement of absorbance in the maximum absorption peak at 484 nm.The optimal conditions including acidity,reagents dosage,surfactant,temperature and time were studied.The linear range was 0-0.4 μg/mL.The apparent molar absorptivity was 1.66×105 L·mol-1·cm-1 and the detection limit was 6.82 μg/L.A great deal of coexistent ions didn't interfere with the determination.The interferences of MnO4-,Pb2+,Fe3+ and Hg2+ could be separated by ascorbic acid-thiohydroxy cotton fiber.The method was applied to the determination of cadmium in river water samples.The results well agreed with those obtained using atomic absorption spectrometry(AAS).The relative standard deviations of 5 determinations were 1.7 %-2.0 % and recoveries were 98 %-100 %.