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 0.6~2.4mol/L HClO4,palladium(Ⅱ)reacted with 5-I-PADAT to form a stable complex,but cobalt(Ⅱ) could not in such a strong acidic medium.Cobalt(Ⅱ)reacted with 5-I-PADAT in the pH 3.6~10buffer medium to form a stable complex which could be converted to another protonated species with higher absorption characteristics when the acidity was increased to 0.6-3.0mol/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 0-0.4μg/mL and 0-1.0μg/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).