Resorcinol Method for Colorimetric Microdetermination of Copper in Pure Forms

A simple colorimetric method is proposed for the micro-determination of copper in pure forms. The assay is based on the formation of a color complex between copper and resorcinol in presence of ammonia with peak absorption at 450 nm. The method is linear over 0.05 through 1.0 μg Cu (R ≥0.99). The regression coefficients vary from 0.275 to 0.920 depending upon the choice of experimental conditions. The assay can be conducted either at room temperature or rapidly by incubating the samples in boiling water bath for 3 minutes. The optimum conditions for the assay and the potential interfering have been identified. The method has been tested for determining copper (I & II) in known aqueous solutions, in freshly synthesized copper (II) nitrate and copper (II) chloride, and for determining traces of copper in reagent grade sodium chloride. The results obtained are comparable to those provided by the dithiocarbamate method with respect to per cent recovery and precision (P > 0.1) with obvious advantages: (i) having at least ten times better detection limit and sensitivity, and (ii) being unaffected by the presence of Cd or Co when used up to 20 μg each per sample.