Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1988-09-28
1990-02-13
Kaplan, G. L.
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204 1T, 204433, 204435, G01N 2730
Patent
active
049004247
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrochemical measurement devices and methods, especially for pH measurement.
Measurement of pH is known to be possible in a variety of ways. A widely-used technique is based on the glass pH electrode, used in conjunction with a reference electrode. Glass pH electrodes are fragile and call for the use of high-impedance electronic instrumentation circuitry engineered to exacting standards.
An early electrochemical method of pH measurement was based on the reversible redox system p-benzoquinone (quinone) and its hydroquinone (quinol), involving production and consumption of protons. (OH).sub.2
An inert electrode, dipping into the solution under test with the addition of excess of the sparingly soluble quinone/quinol mixture, will assume a potential governed by the activity of H.sup.+. This potential can be measured by the inclusion of a conventional reference electrode (e.g. saturated KCl calomel) into the solution, both electrodes connected to a suitable voltmeter. The potential difference at the voltmeter is related to the H.sup.+ activity via the Nernst equation in the following forms: ##EQU1##
The quinhydrone electrode as described above has fallen from favour since about 1928 due to the emergence of practical glass electrodes, owing to the fact that the glass electrode was non-destructive of the liquids to be tested, while the quinhydrone technique required quantities of the liquids under test to be mixed with quinhydrone.
It is an aim of the present invention to provide new robust and convenient arrangements applicable to pH measurement, and to the production of reference electrodes, usable for other electrochemical measurements.
In particular, it is an aim of the present invention to provide arrangements for pH measurement which can be implemented with simplified electronic instrumentation.
It is a further aim of the invention to provide pH measurement cells which give useful consistency and accuracy in measurement in spite of manufacturing variations.
A particular aim of the invention is to provide electrochemical measurement cells which can be made cheaply enough to be single-use disposable devices, in contrast to usual expensive measurement electrodes. Another aim is to provide electrodes and measurement cells that can be manufactured with only small batch-to-batch and within- batch variations. A related aim is to provide electrodes and measurement cells that can be used without individual standardisation and compensation for voltage offset.
According to an aspect of the invention there is provided an electrochemical cell comprising two electrodes, wherein one of said electrodes is suitable for use as a reference electrode in electrochemical measurements, said device comprising (a) a capillary fill cell capable of receiving a small volume of aqueous sample liquid, said cell incorporating (b) a redox electrode located within said capillary fill cell, and (c) a reagent layer comprising quinhydrone located in said cell in a dry adherent water-soluble layer adherent to an inner surface of said cell opposite to or overlying said redox electrode and capable of dissolving during use in aqueous sample liquid in the region of said redox electrode.
Such an electrochemical device can further comprise (d) a reagent layer comprising pH buffer material located in said cell in a dry adherent water-soluble layer adherent to an inner surface of said cell opposite to or overlying said redox electrode and capable of dissolving in aqueous liquid in the region of said redox electrode, thereby to render said redox electrode useful as a reference electrode.
One of said electrodes can be a reference electrode, and a further electrode can in that case constitute said redox electrode (c) and has associated therewith said reagent layer (d) comprising quinhydrone, thereby to render said cell suitable for the measurement of pH in a small quantity of aqueous liquid sample. For example, in one related embodiment a cell suitable for the measurement of pH in a small quantity of aqueous liquid sample com
REFERENCES:
patent: 4454007 (1984-06-01), Pace
Arao Itano, Comptes Rendus des Trauaux do Laboratoire de Carlsborg, vol. 22, pp. 235-237, (1938).
J. Livingston et al., The Electrochemical Soc., Preprint 61-17, pp. 199-218, (1932).
E. Newbery, The Electrochemical Soc., Preprint 65-9, pp. 107-113, (1934).
Birth Brian J.
Burns Ian W.
Kaplan G. L.
Unilever Patent Holdings B.V.
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