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Bestimmung von organischen Substan z en mit Hilfe von elektrolytisch er z eugtem z weiwertigem Silber. Der verwendete Elektrolyt besteht aus 0,1 M Silbernitrat in 5 M Salpetersâure bei-10"C. Die Generatoranode besteht aus Gold (Stromdichte 1,5-5 mA/cm^). Die Bestimmung des Endpunkts erfolgt potentiometrisch (Pt/SKE) oder biamperometrisch (Pt-Elektroden, 200 mV). Fur die potentiometrische Bestimmung wird die Indicatorelektrode mit einer Lôsung von AgO in Salpetersâure oder durch eiektrochemische Anodisierung vorbehandelt. Folgende Substanzen wurden bis herab in den sub-Milligramm-Bereich mit Fehlern von 1-2% titriert: Isoniazid, Oxalyldihydrazid, Hydrochinon, Resorcin. Summary. Conditions are described for the efficient génération of silver(II) and the titration of organic compounds by electrogenerated silver(II). An electrolyte of 0.1 M silver nitrate and 5 M nitric acid at-10 C is used, with a gold generating anode and acurrent density of 1.5-5mA/cm^. A potentiometric(piatinum-S.C.E. pair) or biamperometric (platinum électrodes, 200 mV) end point détection is used. For potentiometric détection, the platinum électrode is preconditioned with AgO in nitric or by anodization. The compounds isoniazid, oxalyldihydrazide, hydroquinone, and resorcinol were titrated down to sub-milligram quantities with errors ofl-2%.

Gold(III) was electrogenerated with high efficiency at constant current in halide média by oxidation of freshly electrodeposited gold on a platinum électrode. The electrolytes tested were 0.0005-1 M HCl, N aCl, HBr, and N aBr. Potentiometric studies indicated that the tetrahaloaurate(III) complex was generated in each case with oxidation potentials ranging from 0.83 to 1.15 V. Arsenicdlll (20 ^eq) was titrated potentiometricallv in 0.1 M NaBr bv using a gold indicating électrode; the efficiency was 99.90 ± 0.05%. Iron(II) was titrated in 0.01 M HCl to a biamperometric end-point with gold-plated platinum wire indicating électrodes polarized at 100 mV. Recoveries were 100.7 ± 1.8% (0.7 mg) and 100.4 + 2.3% (0.4 mg). This new system allows titrations over a wide range of acidities and oxidation potentials.

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