FORMATION AND ANALYTICAL CHARACTERISTICS OF THE IONIC PAIR OF TETRAIODOCADMIATE(II) WITH QUINALDINE RED

Among heavy metal ions, cadmium is one of the most toxic elements entering the ecosystem because of industrial activities. Today, there are a significant number of approaches to the detection and quantitative determination of Cadmium, among which spectrophotometric methods in various modifications occupy an important place, and to increase sensitivity and selectivity, pre concentration methods are used. A feature used to develop extraction-spectrophotometric methods for the determination of cadmium is its ability to form complex anions with halide ions of the composition [CdHal3]- and [CdHal4]2-, which can form ionic pairs with cationic dyes. In this work, the interaction conditions in the chemical system “Cadmium(II) : iodide ion : quinaldine red cation (QR)” were studied and optimized. The optimal conditions for the formation of the ionic pair were determined: pH 4.5; the concentration of iodide ions in the system is 1·10-3 mol/L, and to stabilize the interaction product, 1 ml of a 10 vol.% solution of Triton X-100 must be introduced. The stoichiometric composition of the ionic associate was determined by classical spectrophotometric methods (molar ratio method and chemical equilibria shift method), which gives grounds to write the formula of the ionic pair in the following form (QR)2[CdI4]. It is shown that the developed technique using an analytical form based on an ion pair (QR)2[CdI4] is sufficiently selective. The chemical and analytical characteristics of the analytical form were calculated, and it was established that the calibration graph is linear in the concentration range of 0.2-2.25 mg/L of Cadmium(II), and the detection and determination limits are 0.06 mg/L and 0.2 mg/L, respectively.