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变色酸杂环偶氮试剂是在PAN和PAR之后发展起来的一类杂环偶氮试剂。已研究过的有变色酸吡啶偶氮试剂、变色酸噻唑偶氮试剂、变色酸安替比林偶氮试剂及其双取代衍生物。在H酸杂环偶氮试剂中只研究过H酸吡啶偶氮试剂。由于这两类试剂的灵敏度低于PAN和PAR,选择性也不理想,因此没有得到广泛应用。我们发现,在吡啶环的3位或3,5二位上引入库仑积分较大的溴原子,则可明显地改进试剂的分析性能。实验表明,这类试剂中的5-溴-2-吡啶偶氮变色酸(5-Br-PACh),在强酸介质中是钯的高选择性的灵敏显色剂,在近中性或弱碱性介质中,用分光光度法测定铜、镍、钴、铝,不仅灵敏度高而且选择性也好,在一定的掩蔽剂存在下,可对上述离子直接在水相中比色。
Chromochromic heterocyclic azo reagents are a class of heterocyclic azo reagents developed after PAN and PAR. Have been studied are chromic acid pyridine azo reagent, chromotropic acid thiazole azo reagent, antipyrine acid antipyrine azo reagent and its disubstituted derivatives. Only pyridinium azo reagent H has been studied in the H acid heterocyclic azo reagent. Because these two types of reagents have lower sensitivity than PAN and PAR, their selectivity is not ideal, so they have not been widely used. We found that the introduction of larger Coulomb integral bromine atoms at positions 3 or 3,5 of the pyridine ring significantly improves the analytical performance of the reagents. Experiments show that these reagents 5-Bromo-2-pyridylazo achromic acid (5-Br-PACh), in the strong acid medium is a highly selective and sensitive palladium chromogenic reagent, in the nearly neutral or weak base In the medium, spectrophotometric determination of copper, nickel, cobalt, aluminum, not only high sensitivity and selectivity is also good, in the presence of a certain masking agent, the above ions can be directly in the aqueous colorimetric.