Abstract: Rh(III) may be determined from its catalytic effect on the chemiluminescent reaction between luminol and dissolved O2 in a reverse-micellar medium of cetyltrimethylammonium chloride (I) in cyclohexane/CHCl3 (5:6) and 0.2 M Na2CO3 of pH 12. The luminol reagent was prepared by dispersing 4 µM luminol 0.2 M Na2CO3 in cyclohexane/CHCl3 (5:6) containing 10 mM I to give a surfactant:H2O ratio of 5:111. Sample solution (90 µL) and 100 µL of luminol reagent were introduced into parallel CHCl3 carrier streams (2 ml/min each) and the luminescence produced when the two solution mixed was measured in a 70 µL flow cell that was located in front of a photomultiplier detector. The detection limit was 50 ng/ml of Rh(III) and the calibration graph was linear from 0.4-10 µg/ml of Rh(III).

Abstract: A flow-through microcell with a mercury pool indicator electrode and a Pt-wire auxiliary electrode was used for continuous-flow determination of Rh(III), as [Rh(NH3)5Cl]Cl2 in a pH 9.3 0.1 M NH3 buffer by differential-pulse voltammetry at -1.63 V vs. SCE. The flow-path was 2.0 mm i.d. The peak resolution at a sampling rate of 60/hr was good. The calibration curve had the shape of an adsorption isotherm at 2.0 ppb Rh, typical for catalyzed electrode reactions. The relative standard deviation was 1.1% in the determination of 1.0 ppb Rh. The detection limit was 0.1 ppb rhodium.