Selective Flotation-Separation and Spectrophotometric Determination of Cadmium Using Phenanthraquinone Monophenythiosemicarbazone

Abstract

A simple, selective and sensitive procedure is described for the preconcentration by flotation followed by spectrophotometric determination of trace amounts of Cd(II). Cadmium forms an intense red 1:2 complex with phenanthraquinone monophenylthiosemicarbazone (PPT) at pH ≥ 6. The colored Cd-PPT complex was floated quantitatively with oleic acid (HOL) surfactant at pH 6.5, exhibiting maximum absorbance at 520 nm and having a molar absorptivity of 2.4 × 10⁵ L mol^-1 cm^-1. The stability constant of the formed complex is 1.5 × 10¹²; log K = 12.2. Beer’s law was obeyed over the concentration range 0.01 - 0.34 mg/L. The Sandell sensitivity and relative standard deviation are 0.4 ng/cm² and 2.6%, respectively. The results obtained spectrophotometrically were compared to those obtained by AAS analysis. The analytical parameters affecting flotation and hence determination have been thoroughly investigated. The proposed procedure was successfully applied to the determination of Cd(II) traces in certified and real human hair samples as well as in natural waters. The structure of the complex formed and the mechanism of flotation were proposed.