Determination of trace cadmium by spectrophotometry with Cd~(2+)-SCN~--rhodamine B ternary complex system

In phosphoric acid medium,cadmium could react with thiocyanate and rhodamine B to form stable bluish violet ionic complex in the presence of polyvinyl alcohol and gelatin.Based on this,a new determination method of cadmium by spectrophotometry was established.Under the optimized experimental conditions,the maximum absorption wavelength of complex was 614 nm.The absorbance showed good linearity with the concentration of cadmium in the range of 0-0.5 μg/10mL with correlation coefficient of 0.999 0.The apparent molar absorptivity was 1.47×106 L·mol-1·cm-1,and the detection limit was 0.18 μg/L.A lot of common ions did not interfere with the determination.The interference of Mn2+,Hg2+,Bi2+ and Co2+ could be eliminated by enrichment separation with chitosan and combined masking agents.The proposed method was applied to the determination of trace cadmium in environmental water samples.The results were consistent with those found by atomic absorption spectrometry.The relative standard deviations(RSD) were 1.1 %-3.7 %,and the recoveries were 97 %-103 %.