5-(5-碘-2-吡啶偶氮)-2,4-二氨基甲苯双波长叠加分光光度法同时测定钴和钯

以试剂5-(5-碘-2-吡啶偶氮)-2,4-二氨基甲苯(5-I-PADAT)做显色剂,建立了双波长叠加分光光度法同时测定钴和钯的新方法。研究发现,在0.6~2.4mol/L HClO4介质中,钯(Ⅱ)与5-I-PADAT反应形成稳定络合物,而在此高酸度下,钴(Ⅱ)则完全不能显色;在pH3.6~10的缓冲介质中,钴(Ⅱ)与5-I-PADAT反应形成稳定络合物,钴络合物形成后以强酸酸化,提高酸度至0.6~3.0mol/L HClO4,可转变为另一种具有较高吸收特性质子化型体。研究还发现,钴(Ⅱ)、钯(Ⅱ)与5-I-PADAT形成的络合物,均呈现两个吸收峰,且吸收峰位置十分接近,强峰分别位于580和583nm,弱峰分别位于532和543nm。基于钴(Ⅱ)、钯(Ⅱ)与5-I-PADAT显色酸度的差异以及吸光度的加合性特点,采用双波长叠加,建立了分光光度法同时测定钴和钯的新方法。钴、钯质量浓度分别在0~0.4μg/mL和0~1.0μg/mL范围内服从比尔定律,表观摩尔吸光系数分别为2.17×105 L·mol-1·cm-1和1.10×105 L·mol-1·cm-1,灵敏度较单波长分别提高1.75和1.53倍。方法应用于催化剂和矿样中钴和钯的同时测定,测定值与推荐值相一致,相对标准偏差(RSD,n=6)分别为0.50%~2.3%(钴)和1.0%~1.4%(钯)。

Simultaneous determination of cobalt and palladium by 5-(5-iodine-2-pyridylazo)-2,4-diaminotoluene dual wavelength overlapping spectrophotometry

A novel simultaneous determination method for cobalt and palladium was established by dual wavelength overlapping spectrophotometry with 5-(5-iodine-2-pyridylazo)-2,4-diaminotoluene (5-I-PADAT) as chromogenic reagent. The experimental results showed that in the medium of 0.6~2.4 mol/L HClO₄, palladium reacted with 5-I-PADAT to form a stable complex, but cobalt could not in such a strong acidic medium. Cobalt reacted with 5-I-PADAT in the pH 3.6~10 buffer medium to form a stable complex which could be converted to another protonated species with higher absorption characteristics when the acidity was increased to 0.6-3.0 mol/L HClO₄. It was also found that, the complex of cobalt (Ⅱ) and palladium(Ⅱ) and 5-I-PADAT both have two very close absorption peaks, with strong peak at 580 nm and 583 nm and weak peak at 532 nm and 543 nm, respectively. Based on the difference of chromogenic acidity of cobalt(Ⅱ) and palladium(Ⅱ) with 5-I-PADAT, the absorbance additivity, etc., a novel simultaneous determination method for cobalt and palladium by dual-wavelength overlapping spectrophotometry was estblished. Beer's law was obeyed within cobalt and palladium concentration range of 0-0.4 μg/mL and 0-1.0 μg/mL, respectively. The apparent molar absorption coefficients of cobalt and palladium were 2.17×10⁵ L·mol^-1·cm^-1 and 1.10×10⁵ L·mol^-1·cm^-1, and the sensitivity was improved by 1.75 and 1.53 times higher than single wavelength, respectively. The method has been applied to simultaneous determination of cobalt and palladium in catalyst and ore samples, whose results were consistent with the recommended values. The relative standard deviation(RSD,n=6)were 0.50%-2.3%(cobalt)and 1.0%-1.4%(palladium).