Spectrophotometric determination of available copper in acidic soils using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol

Abstract

A method is described for determining the available copper in acidic soil. The absorbance is measured at 556 nm; the molar absorptivity of the coloured complex is 6.87 × 10⁴ l mol^–1 cm^–1 and the Beer-Lambert law is valid for copper concentrations between 0 and 20 µg per 25 ml. The colour of the complex is stable for at least 2.5 h. The ions normally present in acidic soils do not interfere when ammonium citrate, nitroso-R salt and Chugaev's reagent are added as masking agents. Soils from several sources have been analysed by this method, and the results obtained were satisfactory.