Peroxodisulphate ("persulphate") may be determined by direct current voltammetry (DCV) using carbon paste electrodes chemically modified with Prussian Blue, iron(III)-hexacyanoruthenate(II) or iron(III)-hexacyano-osmate(II). The determination is based on the exploitation of catalytic currents from the reduction of the modifiers. Best results are obtained for iron(III)-hexacyanoosmate(II) yielding a detection limit of 1 μg O22-/ml (as persulphate) when using HCl (10-2 mol/l) as supporting electrolyte and measuring in the DCV-mode. Electrodes doubly-modified with the osmium compound and a liquid anion-exchanger (Amberlite LA2) allow determinations of persulphate after preconcentration under open circuit conditions, in the presence of hydrogen peroxide and perborate, with a detection limit of 20 ng O22-/ml (as persulphate).
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