Abstract
A method is described for the spectrophotometric determination of rhodium. Rhodium (III) reacts with an excess of Xylenol Orange (XO) to form a red chelate having an absorption maximum at 520 mμ, while a blue chelate with its absorption maximum at 598 mμ is formed when an excess of rhodium is present. The former, which was used to the spectrophotometric determination of rhodium, gives the maximum absorbance in the pH range from 2.7 to 3.3. Beer's law is obeyed up to about 60 μg of rhodium in 25 ml. The sensitivity of the reaction is 0.0052 μg Rh per cm2. Among the anions tested, chelating agents such as NTA and EDTA interfere seriously with the determination. The effect of addition of some inorganic acids, on the absorbance of the colored solution, is also examined.
The presence of 1 : 1 chelate is confirmed by the method of Frank and Oswalt. The apparent formation constant of the chelate is calculated to be 2.8 × 103 at pH 2.50.
