First derivative spectrophotometric determination of trace rhodium after preconcentration of its complex on microcrystalline naphthalene

A highly selective, sensitive, rapid and economical method using spectrophotometry has been developed for the determination of trace amounts of rhodium in various synthetic samples after adsorption of its 1-(2-pyridylazo)-2-naphthol complex onto microcrystalline naphthalene. The rhodium complex is quantitatively adsorbed on microcrystalline naphthalene in the pH range of 4.2-5.5. After filtration, the solid mass is dissolved with 5 mi of dimethylformamide and the metal determined by first derivative spectrophotometry. The detection limit is 30 ppb(signal to noise ratio = 2) and the calibration curve is linear over the concentration range 0.1-25 mu g/ml in a dimethylformamide solution with a correlation coefficient of 0.9996. Various parameters such as the effect of pH, volume of aqueous phase and interference of a number of metal ions on the determination of rhodium has been studied in detail to optimize the conditions for determination in synthetic samples.