Spectrophotometric determination of cadmium with 1-(2-pyridylazo)-2-naphthol and non-ionic surfactants Application to acetic acid extracts of ceramic enamels

The Cd-PAN system in the presence of non-ionic surfactants (polyoxyethylene nonylphenols), which dissolve the reagent and complex by formation of micelles, has been studied spectrophotometrically. The optimum conditions for Cd determination are pH 9 (Na₂B₄O₇-HClO₄), 2% of surfactant and measurement at 555 nm. The complex is Cd(PAN)₂ and its conditional formation constant is 3.5 × 10¹¹. The system obeys the Lambert-Beer law, with an error of 0.9% over the Cd concentration range 0.44–1.74 ppm; the molar absorptivity is 4.94 × 10⁴1·mole⁻¹.cm⁻¹ at 555 nm. The relative standard deviation is 0.7% and the limit of detection 0.009 μg/ml. The selectivity with respect to species important in the ceramic industry is adequate for application of the method to determination of Cd in acetic acid extracts of ceramic enamels.