Spectrophotometric Studies on the Complexation Equilibria of Ni and Pb with 2‐Carboxy‐2‐Hydroxy‐5'‐Sulfo‐Formazylbenzene. Simultaneous Determination of Trace Amounts of Ni and Pb

Abstract Spectrophotometric studies have been made to investigate the reaction of Nickel and Lead with 2‐carboxy‐2'‐hydroxy‐5'‐sulfoformazyl‐benzene (zincon) in 50%(v/v) ethanol‐water at 25 °C and an ionic strength of 0.1 M NaClO 4 . A complete picture of the complexation equilibria in the pH range (4.2‐12.0) for nickel and (1.9‐11.5) for lead are presented. Simple, rapid, selective and sensitive methods for the spectro‐photometric determination of nickel and lead has been developed based on the color reaction of their complexes with zincon. The methods allow the determination of 4.69 μg mL ‐1 of nickel at pH = 6.3 (λ max = 665 nm) and 10.3 μg ml ‐1 of lead at pH = 5.6 (λ max = 610 nm). The apparent molar absorptivities were ε = 1.3 × 10 4 L mol ‐1 cm ‐1 for nickel and ε = 0.6 × 10 4 L mol ‐1 cm ‐1 for lead. The interference of a large number of foreign ions and complexing agents has been studied. Thiosulphate, as masking agent allows the simultaneous determination of nickel and lead in the presence of high concentrations of copper. Ascorbic acid, sodium cyanide and or sodium fluoride provide the elimination of many other interferences. The methods have been applied successfully to the simultaneous determination of nickel and lead in an aluminium and non‐ferrous alloy