Cd2+-SCN——罗丹明B三元缔合物体系光度法测定痕量镉

磷酸介质中，在聚乙烯醇和明胶的共同作用下，镉(Ⅱ)能与硫氰酸根和罗丹明B形成稳定的蓝紫色离子缔合物，据此建立了光度法测定镉(Ⅱ)的新方法。在最佳实验条件下，缔合物的最大吸收波长为614 nm，镉(Ⅱ)的浓度在0~0.5 μg/10mL范围内与吸光度呈良好的线性关系，相关系数为0.999 0，表观摩尔吸光系数为1.47×106 L·mol-1·cm-1，检出限为0.18 μg/L。大量的常见离子不干扰测定，Mn2+、Hg2+ 、Bi2+、Co2+的干扰可采用壳聚糖富集分离和联合掩蔽剂消除。方法用于环境水样中痕量镉的测定，结果同原子吸收光谱法相一致，相对标准偏差为1.1％～3.7％，回收率为97％～103％。

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

In phosphoric acid medium, cadmium(Ⅱ) 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(Ⅱ) 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(Ⅱ) 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 %.