On-line preconcentration of rhodium on an anion-exchange resin loaded with 1,5-bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydrazide and its determination in environmental samples

A method for the determination of rhodium in different samples at trace levels is presented. The investigated metal is preconcentrated on a chelating resin microcolumn (1,5-bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydrazide (PSTH) immobilized on an anion-exchange resin (Dowex 1×8-200)) placed in the autosampler arm. The modification of the autosampler in the tubing line and circuit allowed either the flow of the sample through the column or the operation of the autosampler in the normal mode, where microlitres of 4 M HNO₃, which acts as the elution agent, pass through the microcolumn eluting Rh(III), which is directly deposited in the graphite tube as drop of a precisely defined volume. The detection limit is 0.3 ng ml⁻¹. Linearity is maintained in the concentration range 0-50 ng ml⁻¹ for rhodium, with correlation factor of 0.999 and relative standard deviation of 1.8% for 10 ng ml⁻¹ of Rh. The effects of various parameters such as pH, concentration and volume of eluent, sample loading time, sample flow rate and interference of a large number of metal ions and anions on the determination of this metal was studied in detail to optimize the conditions for their determination in various samples. The method is found to be highly selective, fairly sensitive, simple, rapid and economical and may be safely applied to their determination in different complex materials such as environmental samples and catalysts.