SIMULTANEOUS PHOTOMETRIC DETERMINATION OF COBALT AND PALLADIUM WITH 5-(5-NITRO-2-PYRIDYLAZO)-2,4-DIAMINO TOLUENE (5-NO_2-PADAT)

The new reagent, 5-NO2-PADAT, reacts with Pd ( Ⅱ ) in a relatively high acidic medium of 3. 0mol · L-1 H2SO4 , to form a stable coordination complex with its absorption maxima at 591nm. The same reagent reacts with Co( Ⅱ ) in an acetate buffer medium of pH 5. 5 to form a stable coordination complex which keeps unchanged when the acidity of the solution is raised to 3. 0mol · L-1 H2SO4. The absorption maxima of the Co( Ⅱ) complex lies at 586nm. It is found that when the measurement is made at 586nm for both of the complexes of Pd( Ⅱ ) and Co( Ⅱ ), good additivity of the absorbances is obtained. Based on these facts, Co( Ⅱ ) and Pd( Ⅱ) can be determined simultaneously by taking two same aliquots of the sample solution, and carrying out the color reaction in one aliquot at 3. 0mol · L-1H2SO4 with its absorbance APd , and in another aliquot at pH 5. 5 and afterwards acidified to 3. 0mol · L-1 H2SO4 with its absorbance ACo+Pd. The absorbance of the Co( Ⅱ ) complex is obtained by the difference of ACo+Pd and APd. The proposed method has been applied satisfactorily to the analysis of simulated samples containing both Co( Ⅱ ) and Pd( Ⅱ ).