SIMULTANEOUS PHOTOMETRIC DETERMINATION OF COPPER AND PALLADIUM WITH 5-(5-NITRO-2-PYRIDYLAZO)-2,4-DIAMINOTOLUENE

It was found that at room temperature, palladium(Ⅱ) and copper(Ⅱ) react with 5-(5-nitro-2-pyridylazo)-2,4-diaminotoluene (5-NO_2-PADAT) in an acetate buffer medium around pH 5 to form stable complexes having their absorption maxima at 519nm. And in a relatively strong acid medium (e.g. in 0.06～1.5mol·L~(-1) HCl medium, 0.18～4.6mol·L~(-1) H_2SO_4 medium or 0.06～3.6mol·L~(-1) HClO_4 medium) the complex of Pd(Ⅱ) with 5-NO_2-PADAT remains stable and its absorption maxima shifts to 592nm, while copper(Ⅱ) does not react with 5-NO_2-PADAT. It was also found that in the acetate buffer medium, the complex of Cu(Ⅱ) with 5-NO_2-PADAT is decomposed by the addition of EDTA, while the complex of Pd(Ⅱ)-5-NO_2-PADAT remains unchanged. Based on these facts, a method of simultaneous photometric determination of Cu(Ⅱ) and Pd(Ⅱ) is proposed. (Beer′s) law holds in the ranges of 0～0.7μg·ml~(-1) for copper and 0～0.9μg·ml~(-1) for palladium, with their apparent molar absorptivities of e~(519)_(Cu)=6.70×10~4L·mol~(-1)·cm~(-1) and e~(592)_(Pd)=1.25×10~5L·mol~(-1)·cm~(-1). The proposed method has been satisfactorily applied to the analysis of ores and waste water from electroplating plants.