Spectrophotometric Determination of Cobalt(III) and Iron(II) with 4-Hydroxy-2-dimethylamino-5-nitroso-6-aminopyrimidine

Abstract

Methods for the spectrophotometric determination of cobalt(III) and iron(II) with 4-hydroxy2-dimethylamino-5-nitroso-6-aminopyrimidine (HDNA) have been developed. Cobalt(III) reacts with HDNA to form a water-soluble yellow complex having an absorption maximum at 395 nm. Absorbance of the complex is constant over the pH range from 5.5 to 6.8. Beer's law holds over the range from 0 to 1.4 g/ml of cobalt (III), the molar absorptivity of the complex and the Sandell sensitivity for log(Io/I) =0.001 being 6.30 x 104 l. cm-1. mol-1 and 9.34 X 10-4 gcm-2, respectively. Nickel(II) and copper (II) interfere with the determination, but can be masked by the addition of 1% potassium cyanide solution. Iron(II) also forms a watersoluble blue complex with the reagent, having an absorption maximum at 660 nm. Absorbance of the complex is constant over the final pH range from 9.6_to 10.5. The solution containing up to 2.0 g/cm of iron (II) obeys Beer's law. The molar absorptivity of the complex and the sensitivity for log (Io/I) =0.001 are 3.05 x 104 l. cm-1. mol-1 and 1.85 x 10-3 pg. cm-2, respectively. Tolerance limits are given for 19 ions and 6 salts. The ratio of metal to HDNA is found to be 1: 3 for both complexes by the continuous variation method. The present method can be applied to the consecutive spectrophotometric determination of cobalt and iron, and of iron in zinc sulfate and aluminum alloys with a satisfactory result.