GB972172A - Coulometric reagent generator - Google Patents

Abstract

<PICT:0972172/C6-C7/1> In coulometric titration, the reagent is generated in an external cell, and then flows to the titration unit from an electrode zone surrounded by porous element, to avoid disturbing gas reactions due to the electrodes. A suitable apparatus comprises a feed tube 24 through which an electrolyte, e.g. Na2SO4 solution, flows into a cell filled with a uniform glass wool packing 48 through which the electrolyte is distributed uniformly. The acid and alkali products formed at the electrodes 32, 34 flow down trough-shaped drain guides 14, 16 to delivery taps 18 and 20. At low voltage operation and at low flow rates, gases generated at the electrodes escape freely, and the outer surface of the drain guides 14, 16 are open to the air allowing any dissolved gas to escape. The two streams may be used for independent titrations, the quantity of reagent required to reach the "end-point" being measured by the quantity of electric power used. Instead of acid/base generation, silver ions can be generated using a silver anode and an acetate buffer solution as electrolyte. Potassium iodide and other salts are also referred to. In modifications, the glass wool packing is replaced by a pair of porous diaphragms of glass frit, within which is mounted metal gauze or a coiled Pt wire electrode spring-pressed against the diaphragms which are more porous on the remote faces to assist escape of gases. The drain tubes are preferably of a wettable material, e.g. P.V.C., and the casing of a non-wettable material, e.g. P.T.F.E. or polythene. The reagents flowing down the drain tubes may be washed down by inflowing a supplementary stream of pure water; and a purging gas may be admitted, e.g. N, to prevent oxidation. In other forms, two electrode spaces are formed for two electrolytes, one of which may be a non-treated electrolyte, and a differential hydrostatic pressure is maintained to provide different rates of out-flow of reagents generated.