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The electrochemistry of Rh(NH3),0HZ+ has been studied in a buffered ammoniacal solution. The polarographic reduction wave at the dropping mercury electrode had equal to -1.10 V (vs. saturated calomel electrode) in a 0.10 M N H , -0.10 MNH,C10, electrolyte, and gross Hg cathode electrolysis at -1.19 V produced a stable Rh(NH3),Hz+ hydride species. Both reductions were found to take place through a Rh(I) intermediate.The reaction of the Rh(NH3),HZ+ with molecular OZ in the ammoniacal electrolyte was also studied. The product was demonstrated to be a stable Rh(NH3)4(0H)(OZH)+ hydroperoxo species.

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A method is described for the determination of aluminium in aqueous samples by linear scan voltammetry after adsorptive accumulation of the pyrocatechol violet (PCV) complex. A pH 6.5 triethanolaminelperchloric acid electrolyte is used for the determination with adsorption onto a mercury drop electrode at -0.50 V (vs a AglAgCVsatd KC1 reference). Scanning cathodically after adsorption gave a current peak at -0.70 V for reduction of adsorbed PCV and a peak at -0.90 V for reduction of the adsorbed Al-PCV complex. The peaks were well resolved. Using 1.0 FM PCV and a 60 s adsorption period gave linear calibration curves for A1 in the range 1 to 25 ng mL-' Al. The detection limit was 0.1 ng mL-' Al. For analysis, calibration by the method of standard additions is required. Most other metal species do not interfere, but vanadium (V(IV) and V(V)) forms a complex with PCV that is adsorbed and reduced at the same potential as AI-PCV. The interference may be eliminated by complexation of the V with citrate. A1 and V present together may be determined by analysis in the absence of citrate (total: A1 + V) and in the presence of citrate (Al); V is determined as the difference in the two values.The analysis of a range of samples with A1 concentrations from 6 ng mL-' to 3 yg mL-' gave results which were in good agreement with those obtained by other methods.Key words: aluminium, pyrocatechol violet, adsorption, voltammetry, environmental.