Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment
Patent
1996-05-28
1997-12-09
Valentine, Donald R.
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
204250, 204251, 204275, 204219, C25B 900, C25B 1118
Patent
active
056956304
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a voltammetric method and apparatus for coating an electrode end thus providing, in one instance, a mercury electrode for use in a sensor system.
2. Discussion of Prior Art
There are various methods by which ions can be generated within a solution. One such method is the dissolution of either an anode or cathode which are located within the solution by passing a current between the anode and cathode. Patent EP-O 409,705 discloses apparatus where the dissolution of either the anode or cathode can be controlled so that the concentration of the ions generated are controlled by controlling the amount of current which passes between the anode or cathode. The anode and cathode are solid and are located directly within the solution.
Many analytical procedures involving the determination of substances, additives or contaminants within a sample solution employ the use of mercury film electrodes. Mercury film electrodes are used to determine pollutant species in the environment. It is therefore desirable to ensure that the provision of a mercury film electrode does not itself contribute to an increase of pollutants in the environment. Many methods which rely upon the use of mercury to produce a mercury film on an electrode for use in analytical procedure are fraught with contamination difficulties. The use of mercury poses a hazard, even though it is typically used at very low concentrations, in the order of 10.sup.-6 M to 10.sup.-4 M. Despite this relatively low concentration, its release into the environment is still undesirable. Therefore, the apparatus disclosed in Patent EP-O-P 409,705 would not be suitable in a situation where mercury ions are required. The mercury, which is a liquid, would be in direct contact with the solution and therefore would mix with the solution.
It follows that the control of, and where possible, the recovery of the hazardous chemical species is desirable.
Hitherto, mercury has been deposited within a fluid sample flow using standard dissolution techniques, such as dissolving mercury salt pellets in the fluid sample. Where appropriate, the mercury can be absorbed onto an electrode's surface from the fluid sample by the application of an electric potential. Since mercury salts are particularly soluble, retaining acceptable concentrations of mercury in solution over relatively long periods of time can be problematical.
It is therefore the object of the present invention to provide an apparatus and method which overcomes or at least mitigates the above disadvantages.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided an apparatus for adding mercury ions to a sample fluid within a flow-through sensor system comprising housing means, at least part of which is in fluid connection with a main sample stream conduit, at least part of the housing means in fluid connection with the main sample stream conduit being semi-permeable; that it would be in direct electrical contact only with the mercury when the mercury is located within the housing means; the main sample stream conduit: housing means end an electrical current is passed between the first and second electrodes, mercury ions are formed in the housing means which then are then able to migrate from the housing means via the semi-permeable part into the main sample stream conduit.
It will be apparent to those skilled in the art that mercury metal dissolves under the influence of an electrical potential between two electrodes to form mercury ions. This phenomena is the basis on which the present invention operates.
One advantage of the present invention is that the quantity of mercury ions produced can be controlled, enabling pre-determined amounts to be introduced into a system. This is achieved by using pre-determined amounts of current, the amounts of current usually being very small. Further, the apparatus can operate for very long periods, many weeks, before requiring attention such as maintenance which would consi
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patent: 2289611 (1942-07-01), Wallace
patent: 2500284 (1950-03-01), Heyrovsky
patent: 2835631 (1958-05-01), Metcalf et al.
patent: 3808116 (1974-04-01), Webb
patent: 4661210 (1987-04-01), Tenygl
patent: 4917781 (1990-04-01), Sharifian et al.
The Secretary of State for Defence in Her Britannic Majesty's Go
Valentine Donald R.
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