Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Involving measuring – analyzing – or testing during synthesis
Patent
1995-11-03
1998-11-24
Gorgos, Kathryn L.
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Involving measuring, analyzing, or testing during synthesis
205498, 205510, 205633, 205778, 2057925, 205793, C25B 1502, C25B 124, C25B 116, C25C 100
Patent
active
058401717
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of PCT/GB93/02615, filed Dec. 21, 1993.
FIELD OF INVENTION
This invention concerns electrochemical reactions.
BACKGROUND TO THE INVENTION
There are circumstances involving electrochemical reactions when it is necessary to provide a particular environment, e.g. alkaline conditions, for a reaction of interest to take place, or in which a particular reagent, e.g. hydrogen ions, is required to participate in a reaction of interest. Hitherto this has generally been achieved by supplying an appropriate reagent to the reaction mixture, e.g. by depositing a releasable layer of reagent within an electrochemical cell or by supplying reagent in solution to the cell. Practical difficulties can arise in certain situations. For example it can be difficult to deposit more than one layer of reagent in such a way that all layers are efficiently released into solution. Further, supplying a measured or known quantity of reagent in solution requires appropriately accurate measurement. The present invention provides an alternative approach.
SUMMARY OF THE INVENTION
In one aspect the present invention provides an electrochemical reaction, wherein a controlled amount of a first reagent is generated electrochemically at an electrode in electrical contact with a solution of an electrochemically inert salt, comprising applying a suitable electrical potential to the electrode for a suitable time to generate a controlled amount of the first reagent by electrochemical reaction between the electrode and a species in solution producing a localized thin layer environment comprising the first reagent in the vicinity of the electrode; and monitoring the amount or presence of the first reagent or a further species produced in solution in response to production of the first reagent.
The term "thin layer" as used in this specification means having a thickness less than 1 mm, preferably in the range 0.1 to 0.2 mm.
The method of the invention thus involves generating the first reagent in situ at an electrode. Diffusion of the reagent in solution surrounding the electrode will result in creation of a localized environment of the reagent in the vicinity of the electrode, with the amount of reagent depending on the generating current and the length of time for which it is applied, and so being readily and easily controllable.
Reagent generated by this approach can be used in two main ways: place, e.g. to provide an alkaline environment prior to electrochemical measurement of reducing sugar content of a solution, as disclosed in the specification of British Patent Application No. 9325189.0. In this case the concentration of reagent within the localized environment is not critical. It is merely sufficient that a specified minimum concentration is provided or exceeded. with an analyte, e.g. hydrogen ions for use in a pH titration measurement. In this case it is necessary to provide a precise known amount of reagent at known time.
These two ways could also be used together, with the first reagent providing a necessary environment and reacting stoichiometrically.
The first reagent may comprise hydrogen ions or hydroxyl ions. These are readily produced by application of an electrical potential to water, e.g. an aqueous solution of a reactant. Depending on the polarity of charge at an electrode, water is broken down according to the following equations: ##STR1##
Thus, at the anode hydroxyl ions are produced together with hydrogen gas, while at the cathode hydrogen ions are produced together with oxygen gas.
Other reagents, such as chlorine, bromine, and iodine, can alternatively be produced as the first reagent, by treatment of suitable salt solutions, e.g. KCl, KBr, KI.
The first reagent may be used to generate a further reagent to create a desired environment or participate in a desired reaction. For example, by covering, the electrode with an ion-exchange membrane containing an ion of interest, reagent such as EDTA can be expelled from the membrane in response to contact with hydroxyl ions generated at the
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Birch Brian Jeffrey
Morris Nicholas Andrew
Carroll Chrisman D.
Gorgos Kathryn L.
Unilever Patent Holdings BV
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