Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For corrosion
Patent
1998-07-14
2000-10-10
Tung, T.
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For corrosion
204400, G01N 2726
Patent
active
061298328
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention refers to a device and a method by which the ion concentration in a solution can be adjusted, regulated and measured amperometrically. The invention relates in particular to a device for adjusting and regulating pH values.
In the field of pH adjustment it is common, especially in laboratories, to adjust pH by titration with solutions (usually acids and bases). Adjustment of the pH value in this way is only possible by increasing volume, which, especially with small quantities of solution, is substantial or difficult to dose. What is more, considerable effort is involved in adjusting unbuffered solutions to an accuracy in the range 1/10 or 1/100 of pH. Diluted acids and bases are used to achieve this accuracy, which contributes further to the drawback of increased volume. Automation is elaborate and complicated because of the means of dosing that are needed. It is also common to titrate ions with the aid of current flow (e.g. Nagy, G. et al., E. Anal. Chim. Acta, 91 [1977] 87). But the device involved presents the disadvantage that electrodes are immersed direct in the solution to be titrated. This can lead to unacceptable electrode reactions with formation of radicals, especially on the anode.
The greatest problems result when adjusting pH values in volumes in the ml region and below, these being indispensable in particular for genetic, diagnostic medical and biochemical methods. Simply filling a solution from one plastic vessel into another produces uncontrolled pH alterations of up to half a unit and more, which can be explained by the surface properties of these vessels (clinging molecules, ion exchanger characteristics, etc). These changes are currently tolerated, or they are countered by elaborate rinsing with large consumption of solution. Added to this is the fact that the pH value often has to be controlled and possibly readjusted in small volumes (especially in diagnostic medical, biotechnical or pure technical routine chores), and here a change in volume and the associated alteration of the chemical solution is entirely unacceptable, or the disadvantages are recognized and tolerated. For this reason, in techniques that must make do with a very limited volume of solution, it is scarcely possible at present to correct pH, which can repeatedly cause inaccuracies in tests and reaction conditions.
Other principles are familiar where pH alterations are produced by electrolytically generated ion currents. Use is made here of the classic principle whereby, in electrolysis of a salt (e.g. NaNO.sub.3), the anode region becomes more acidic because of the accumulation of anions (e.g. NO.sub.3.sup.-) and the cathode region more basic as a result of the accumulation of cations (e.g. Na.sup.+). The cause of this is to be found in the redox reactions on the electrodes.
The transport processes involved in pH shifts are described in more detail in what follows.
In theory, every pH shift--whether intentional or unintentional, whether on electrodes or in a free solution--is based on the fact that, in the solution considered, there is a shift in the difference between the sum of all cations minus the sum of all anions (whereby the H.sup.+ and OH.sup.- ions are to be left out of the calculation). A method that influences the pH value of a solution by electrical means must consequently be able to alter this difference. The necessary prerequisites for this are already to be found in the classic works of Kohlrausch (Ann. d. Phys., 62 [1897] 209), Logsworth (J. Am. Chem. Soc., 67 [1945] 1109) and MacInnes (The Principles of Electrochemistry, Reinhold Publ. Co., New York, 1939) and will be explained taking an NaNO.sub.3 solution as an example:
The Na.sup.+ concentration must be increased and/or the NO.sub.3.sup.- concentration reduced to make the solution more basic. If Regulation is to be by electrical means, this means that the number of Na ions introduced to the solution electrically must be greater than the number of Na ions simultaneously escaping.
In a current-carrying elect
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Fuhr Gunter
Hagedorn Rolf
Gunter Fuhr
Noguerola Albi
Tung T.
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