摘要:
基于Co(Ⅱ)、Pd(Ⅱ)与4-(5-硝基-2-吡啶偶氮)-1,3-二氨基苯(5-NO2-PADAB)在不同酸度介质中显色的差异,建立了差减法同时测定钴和钯的方法.在室温下,Co(Ⅱ)与5-NO2-PADAB仅能在pH 6.2～8.0定量反应,钴配合物形成后即非常稳定,加酸酸化后,其最大吸收波长由518 nm红移至580 nm,且灵敏度显著提高;而在强酸性介质中仅Pd(Ⅱ)与5-NO2-PADAB能发生显色反应,其最大吸收波长位于586 nm.在586 nm处,钴、钯配合物吸光度具有良好的加和性,其表观摩尔吸光系数分别为1.28×105 L·mol-1·cm-1和1.04×105 L·mol-1·cm-1.钴、钯的浓度分别在0～0.48 mg/L和0～1.2 mg/L符合比尔定律.所拟方法已用于矿样中钴、钯的同时测定,结果与原子吸收法相符,相对标准偏差(RSD,n=6)分别为1.6%和1.0%.
Abstract:
A new substraction spectrophotometric method for the simultaneous determination of cobalt and palladium with 4-(5-nitro-2-pyridylzao)1,3-diaminobenzene（5-NO2-PADAB） has been developed. The method is based on the chromatogenic differences in the different acidity conditions between the complexes of the two kinds of metallic ions with 5-NO2-PADAB. At the room temperature Co(Ⅱ) reacts with 5-NO2-PADAB and forms a stable complex at pH 6.2～8.0 and further acidification makes the maximum absorption wavelength of the complex shift from 518 nm to 580 nm with remarkable sensitivity improvement. While Pd(Ⅱ) reacts with 5-NO2-PADAB quantitatively in strong acid medium and forms a complex with the maximum absorption wavelength at 586 nm. At 586 nm the absorption of the complexes of Pd(Ⅱ) and Co(Ⅱ) shows a good addictive property with molar absorptivity of εCo=1.28×105 L·mol-1·cm-1 and εPd=1.04×105 L·mol-1·cm-1respectively. Beer′s law is obeyed in the concentration ranges of 0~0.48 mg/L for Co and 0~1.2 mg/L for Pd. The method has been applied to the simultaneous determination of trace Co and Pd in ores. And the results are in agreement with those from AAS with precision (n＝6）of 1.6%RSD for Co and 1.0%RSD for Pd respectively.
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