Spectrophotometric determination of cadmium(II) with 8-quinolinol-5-sulfonic acid after sepa-ration as an ion-pair of tetraiodocadmate (II) ion with trioctylmethylammonium cation

Abstract

Cadmium (II) reacts with 8-quinolinol-5-sulfonic acid (H₂qs) in weakly alkaline media and forms a chelate anion, which is extracted into xylene as an ion-pair with a cation of trioctylmethylammonium iodide (QI). The ternary complex has an absorption maximum at 405nm and the absorbance is constant in the pH range from 8.9 to 9.2. The composition of the complex is estimated to be [Cd²⁺(qs^2-)₂(Hqs^-)-(Q⁺)₃]₀.The recommended procedure is as follows. To a cadmium (II) amount of (5.645.0)μg is added 5 ml of 1 M potassium iodide solution. The solution is diluted to 50 ml with water and shaken with 10 ml of 1% QI-xylene solution. The organic layer is washed twice with water and is transferred into a beaker containing anhydrous sodium sulfate to dehydrate. Then, a 5-ml portion of the extract is taken into another separatory funnel. After addition of 2 ml of 0.01 M NaHqs solution and 10 ml of borax-KH₂PO₄ buffer solution (pH 9.1), the mixture is shaken for 5 min and allowed to stand for 5 min. The organic layer is dehydrated as above and subjected to optical measurements after 30 min. Beer's law holds for cadmium (II) in (0.524.19)μg per ml of the extract with the molar absorption coefficient of (1.04±0.08)×10⁴ cm^-1 mol^-1 dm³. Lead(II) and bismuth(III) interfere with the determination.