An improved colorimetric determination of micro amounts of chromium(VI) and chromium(III) using p-aminoacetophenone and phloroglucinol in different samples

The reaction of Cr(VI) with hydroxylamine resulting in its oxidation to nitrite has been utilized for the determination of chromium. The nitrite thus liberated diazotizes p-aminoacetophenone to form diazonium salt which is further coupled with phloroglucinol in an alkaline medium, to form an azo dye. The dye gave maximum absorbance at 420 nm and when extracted in an amino cartridge obeyed Beer's law in the range from 0.04 to 0.36 mu g/mL of Cr(VI) and has a molar absorptivity of 1.04 x 10(5) L/mol cm. Optimum reaction conditions for diazotization, full colour development and the effect of variables such as temperature, time, and pH have been studied. The proposed method was applied to the determination of chromium in certified samples, air particulates, industrial effluents, and pharmaceutical preparations. The results are in agreement with those obtained by atomic absorption spectrometry.