Santiago de Jesus D, Souza de Carvalho M, Spínola Costa A C, Costa Ferreira S L
Centro Federal de Educação Tecnológica da Bahia, SSA-Bahia, Brazil.
Talanta. 1998 Aug;46(6):1525-30. doi: 10.1016/s0039-9140(98)00025-3.
A system for separation of zinc traces from large amounts of cadmium is proposed in this paper. It is based on the solid-phase extraction of the zinc in the form of thiocyanate complexes by the polyurethane foam. The following parameters were studied: effect of pH and of the thiocyanate concentration on the zinc extraction, shaking time required for quantitative extraction, amount of PU foam necessary for complete extraction, conditions for the separation of zinc from cadmium, influence of other cations and anions on the zinc sorption by PU foam, and required conditions for back extraction of zinc from the PU foam. The results show that zinc traces can be separated from large amounts of cadmium at pH 3.0+/-0.50, with the range of thiocyanate concentration from 0.15 to 0.20 mol l(-1), and the shaking time of 5 min. The back extraction of zinc can be done by shaking it with water for 10 min. Calcium, barium, strontium, magnesium, aluminum, nickel and iron(II) are efficiently separated. Iron(III), copper(II) and cobalt(II) are extracted simultaneously with zinc, but the iron reduction with ascorbic acid and the use of citrate to mask copper(II) and cobalt(II) increase the selectivity of the zinc extraction. The anions nitrate, chloride, sulfate, acetate, thiosulphate, tartarate, oxalate, fluoride, citrate, and carbonate do not affect the zinc extraction. Phosphate and EDTA must be absent. The method proposed was applied to determine zinc in cadmium salts using 4-(2-pyridylazo)-resorcinol (PAR) as a spectrophotometric reagent. The result achieved did not show significant difference in the accuracy and precision (95% confidence level) with those obtained by ICP-AES analysis.
本文提出了一种从大量镉中分离痕量锌的系统。该系统基于聚氨酯泡沫对硫氰酸络合物形式的锌进行固相萃取。研究了以下参数：pH值和硫氰酸盐浓度对锌萃取的影响、定量萃取所需的振荡时间、完全萃取所需的聚氨酯泡沫量、锌与镉的分离条件、其他阳离子和阴离子对聚氨酯泡沫吸附锌的影响以及从聚氨酯泡沫中反萃取锌所需的条件。结果表明，在pH值为3.0±0.50、硫氰酸盐浓度范围为0.15至0.20 mol l(-1)且振荡时间为5分钟的条件下，痕量锌可从大量镉中分离出来。锌的反萃取可通过与水振荡10分钟来完成。钙、钡、锶、镁、铝、镍和铁(II)能有效分离。铁(III)、铜(II)和钴(II)与锌同时被萃取，但用抗坏血酸还原铁以及用柠檬酸盐掩蔽铜(II)和钴(II)可提高锌萃取的选择性。硝酸根、氯离子、硫酸根、醋酸根、硫代硫酸根、酒石酸根、草酸根、氟离子、柠檬酸根和碳酸根等阴离子不影响锌的萃取。必须不存在磷酸根和EDTA。所提出的方法应用于使用4-(2-吡啶偶氮)-间苯二酚(PAR)作为分光光度试剂测定镉盐中的锌。所得结果在准确度和精密度(95%置信水平)方面与通过电感耦合等离子体原子发射光谱法(ICP-AES)分析获得的结果没有显著差异。
