Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For corrosion
Patent
1998-03-13
2000-02-08
Warden, Sr., Robert J.
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For corrosion
2057895, 204409, 204412, 204413, G01F 164, G01N 1700, G01N 2726
Patent
active
060224703
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an improved voltammetric cell, particularly, though not exclusively, of the dropping mercury electrode (hereinafter DME) type, very suitable for industrial use, and is characterized by high reliability, ease of operation and long life.
BACKGROUND OF THE INVENTION
Electrochemical detector and voltammetric cells are known in the art and have been used with success for the analysis of flowing solution in the laboratory. Two-electrode and three-electrode cells are known. The three-electrode cell comprises a working electrode, a counter-electrode and a reference electrode which has the function of establishing and maintaining a constant potential relative to the working electrode or the sample solution. The sample solution is flown continuously through the cell. In principle, the electrodes may be affected by poisoning due to absorption with resulting passivation and loss of signaL In order to avoid such poisoning, the dropping mercury electrode has been adopted in many such cells.
U.S. Pat. No. 3,922,205 describes the basic structure of a polarographic-cell. U.S. Pat. No. 4,138,322 discloses a structure of shielded dropping mercury cathode. U.S. Pat. No. 4,260,467 describes a dropping mercury electrode which comprises a reservoir for liquid mercury, a mercury capillary at the outlet end of which mercury drops are formed, and a valve for selective air-purging passage of mercury from the reservoir to the inlet end of the capillary. An automated polarographic cell is described by C. N. Yarnitzky in Analytical Chemistry, Vol. 57, No. 9, August 1985, p. 2011-2015.
The efficiency of polarographic cells of the aforesaid type depends on the combination of a number of structural and fuctional features. A fully satisfactory combination, providing an industrially efficient such cell has not been achieved so far in the art. The cells which are automatic and also on-line are expensive and not adequately efficient. In many cases, the prior art cells use a solid electrode which becomes polluted with time, so that the cell ceases to be reliable. In on-line, in-flow cells, the signal obtained is often proportional to the Reynolds number. Because of this, attempts have been made to design small cells, having high Reynolds number, comprising means for producing and controlling the dropping of the mercury electrode. Such means, however, being complicated and unreliable. Other cells are objectionable in that they require a very large volume of the sample solution, with resulting waste of time and chemicals.
High sensitivity and short reaction time, viz. quick response, are particularly important in on-line cells and esing cells are not satisfactory in this respect. If, for instance, metal pollution occurs in an on-line system in which such a cell is inserted, a delayed reaction on the part of the cell and the consequent failure to reveal the pollution until a significant period of time has elapsed and the pollution may have reached a high level, negatively affects the operation of the system.
Among the specific problems encountered by polarographic cells employing a dropping mercury electrode of the prior art, two are particularly important. Firstly, the presence of oxygen in sample solution having a strong negative effect on the accuracy of the measurements, the oxygen must be removed as fully as possible before all the solution is fed into the polarographic cell proper. For this purpose, it has been proposed to cause the sample solution to flow in a thin layer, together with a stream of nitrogen, in a tube which leads it close to the position at which the mercury drops are formed. This arrangement, however, has been found to be unsatisfactory, and it is believed that this is due to the fact that it does not assure that the space between the counter-electrode, the reference electrode and the working electrode be always full with the sample solution, and consequently, the electrical contact between the electrodes is interrupted at times, thereby requiring interrupting the measur
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Lieberstein Eugene
Meller Michael N.
Olsen Kaj K.
VerdEco Technologies Ltd.
Warden, Sr. Robert J.
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