Spectrophotometric determination of trace rhodium(III) with molybdate-ethyl rhodamine B-PVA124 system

Rhodium(III) can be determined with various Chromogenic agents such as Malachite green and Rhodamine 6G. In most methods the sensitivity is very poor. The colour reaction of rhodium(III)-molybdate-ethyl rhodamine B(ERB) system has not been reported to date. Rhodium(III) reacts with ammonium molybdate and ERB to form an ion-association complex in the presence of polyvinyl alcohol (PVA). The additions of 5.5-6.5 mL of 5.8 mol/L perchloric acid, 1.5-2.5 mL of 0.2% ammonium molybdate, 0.5-3.0 mL of 2% PVA and 2.5-3.5 mL 0.02% ERB solution result in a maximum and constant absorbance for the ion-association complex. Thus use of 6.0, 1.5, 1.0 and 2.5 mL are recommended, respectively. Beer's law is obeyed in the range of 0 to 2.0 μg/25 mL for rhodium(III). The linear regression equation obtained was A = -0.0036 + 0.2543C (μg/25 mL), (r=0.9994). From the equation the molar absorptivity was calculated to be 6.69 × 105 L · mol-1 · cm-1 at 575 nm. The ion-association complex was stable for at least 48h. The molar ratio of Rhodium(III) to ERB in the ion-association complex establish to be 1:4. The influence of diverse 40 ions was examined. The relative standard deviation for eleven replicate determinations of 1.5 μg/25 mL rhodium was 2.3%. The detection limit was 0.52 μg/L (n=11). The method was has been used to determine trace rhodium in some catalyst and metallurgical products with the recovery of 98-99%, with relative standard deviations of 1.8-2.3%.