Determination of the iridium micro-concentrations using a kinetic catalytic method
The catalytic effect of iridium on the oxidation of water-soluble porphyrin - 5,10,15,20-tetrakis (4-sulfo-natophenyl) porphin (TSPP) with sodium periodate is studied for the first time. A method for determination of the iridium micro-content by the catalytic effect of iridium on the oxidation of water-soluble porphyrin 5,10,15,20-tetrakis (4-sulfonatophenyl) porphin with sodium periodate in a flow-injection system is developed. The lower limit of the determined iridium concentrations is 0.2 x 10<sup>-5</sup> gg/ml (P = 0.95), which is lower than that for the methods described in the literature. Optimal conditions for determination have been specified: pH 3; concentration of the reagents in the flows of a given hydraulic mixing scheme 0.5 x 10<sup>-5</sup> M TSPP and 0.15 M NaIO<sub>4</sub>; room temperature for the indicator reaction. A linear calibration characteristic was obtained under chosen optimal conditions in the range of iridium concentrations (0.2 - 2.0) x 10 - 5 gg/ml. The effect of the elements accompanying iridium in industrial and natural materials was studied. Molar excesses of platinum and non-ferrous metals do not interfere with iridium determination: 20-fold Rh (III); 15-fold Pt (IV) and Fe (II); and 20-fold molar excess of Ni (II). Correctness of the results is confirmed by spike recovery tests on model iridium-containing solutions. S<sub>r</sub> of the results of iridium determination under selected conditions at n = 3, P = 0.95 on model solutions is no more than 0.04. A comparison of the obtained results with literature data showed that the main advantages of the proposed method for iridium determination are room temperature of the reaction, more simple hardware design and lower limit of the iridium determination.