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2-(5-溴-吡啶偶氮)5-二乙氨基酚(5-Br-PAD-AP)作为显色剂已被广泛用于测定许多金属元素。我们在研究了铌、钒与该试剂显色反应的基础上,继续研究了5-Br-PADAP与钴的显色反应,发现5-Br-PADAP不但能在pH3～5测定钴,在有辅助络合剂氟化物的条件下,在较高的酸度下(0.01～0.30N硫酸)还能生成多元有色络合物。高酸度下显色提高了选择性,有利于对干扰元素的掩蔽,大最镍可被氨三乙酸掩蔽,给直接测定镍中微量钴创造了条件。试验表明:紫红色的5-Br-PADAP-Co络合物在540～590nm处有最大吸收,络合物组成Co:5-Br-PADAP=1:2,摩尔吸光系数9.0×10~4,桑德尔灵敏度0.0007μg·cm~(-2),钴的含量在0～12.5微克/25毫升服从比耳定律。
2- (5-Bromo-pyridylazo) 5-diethylaminophenol (5-Br-PAD-AP) has been widely used as a chromogenic reagent in the determination of many metal elements. We studied the color reaction of 5-Br-PADAP with cobalt based on the color reaction of niobium and vanadium with this reagent. We found that 5-Br-PADAP can not only measure cobalt at pH 3-5, Complexing agent fluoride, the higher acidity (0.01 ~ 0.30N sulfuric acid) can also generate a multi-colored complex. Coloring at high acidity improves selectivity, which is good for masking interfering elements. Large nickel can be masked by nitrilotriacetic acid, which provides the conditions for direct determination of trace cobalt in nickel. The results showed that the complex of fuchsine 5-Br-PADAP-Co had the maximum absorbance at 540-590 nm. The complex was composed of 5-Br-PADAP = 1: 2 and molar extinction coefficient 9.0 × 10-4. Sander sensitivity of 0.0007μg · cm ~ (-2), cobalt content of 0 ~ 12.5μg / 25ml subject to Beer’s law.