新显色剂2-(5-羧基三氮唑偶氮)-5-二乙氨基苯甲酸的合成及其与钴的显色反应

Synthesis of 2-(5-carboxy-triazolylazo)-5-diethylamino benzoic acid and its color reaction with cobalt

介绍了新显色剂 2 (5 羧基 三氮唑偶氮 ) 5 二乙氨基苯甲酸 (简称CTZDBA)的合成。经元素分析、红外光谱、紫外光谱、核磁共振谱等方法测试 ,确定其组成和结构。研究了试剂的性质及其与一些金属离子的显色反应 ,建立了光度法测定钴的新方法。结果表明 ,试剂的各级酸离解常数为 :pK1 =3 2 ,pK2 =10 5 ;在pH9 0的NH3·H2 O -NH4 Cl缓冲溶液中 ,CTZDBA与Co2 + 形成稳定的紫红色络合物 ,λmax=62 3nm ,试剂的λmax为 484nm ,Δλ为 13 9nm ,络合比Co2 + :R =1:3 ,Co2 + 在0～ 0 4mg/L范围内服从比尔定律 ,其表观摩尔吸光系数为 8 11× 10 4 。络合物一旦形成后在强酸溶液中能稳定存在 ,可消除大量金属离子的干扰 ,具有良好的选择性。方法可以不经分离直接测定维生素B1 2 和工业废水中的微量钴 ,结果与火焰原子吸收法相符 ,加标回收率为 99 6%～ 10 1 1% ,RSD(n =6)为 0 5 %～ 3 1%。

The synthesis of reagent 2-(5-carboxy-triazolylazo)-5-diethylamino benzoic acid (abbreviated as CTZDBA) and the conditions of its reaction with Co^(2+) are reported.The structure of the reagent is determined by elemental analysis,UV spectrometry,IR spectrocopy and ~1HNMR spectroscopy.Its dissociation constants are pK_1=3.2,pK_2=10.5.The reagent reacts with Co^(2+) to form a stable red complex(1:3 by mole) in the medium of NH_3·H_2O-NH_4Cl at pH9.0.The maximum absorption wavelength and apparent molar absorptivity are 623nm and 8.11×10~4L·mol^(-1)·cm^(-1).Beer's law is obeyed in the range of 0-0.4mg/L for cobalt.The complex will not be decomposed by acidifying with some strong mineral acids,while complexes formed by other coexisting ions and CTZDBA will be decomposed,thus the selectivity is improved.The method has been applied to the direct determination of cobalt in VB_(12) and waste water with satisfactory results.The recovery of standard addition is 99.6%-101.1% with RSD of 0.5%-3.1%(n=6).