RU8480U1 - COMPARISON ELECTRODE FOR POTENTIOMETRIC MEASUREMENTS - Google Patents

Description

Reference electrode for potentiometric measurements

The utility model relates to physical, analytical and electrochemistry and can be used to measure the potentials of electrodes in solutions.

The main requirement for the reference electrode is the independence of its potential on the concentration (activity) of ions and electrons in solution, current density and other parameters.

Silver chloride, calomel and some other reference electrodes are known 1, pp. 75-114, 2, pp. 115-117.

Each of these reference electrodes contains a metal (mercury, silver, thallium amalgam) electrode immersed in a solution in contact with a sparingly soluble metal salt napstsyvaya solution, and having a constant high concentration of the second co.im, which contains the same anion, like salt napstsatyvaya solution. A solution with a metal electrode immersed in it fills the housing and connects to the external solution through an electrolytic contact, i.e. the part of the housing in which ion current is possible between the solutions in the housing and externally without noticeable mixing of the solutions. The electrolytic contact is performed in the form of a porous ceramic insert in the housing or in the form of a slit, or in other ways 1, pp. 88-100.

GOIN 27/00

the ability to maintain a higher pressure of the potassium chloride solution compared to the external environment so that, within the electrolytic contact zone, high (compared to the external environment) conductivity is maintained due to potassium chloride 1, p 104. In the worst case, in the contact zone due to diffusion from ions with a different mobility than that of potassium and chlorine ions, which will lead to an increase in the diffusion potential, i.e. to potentiometric measurement error. This also determines the so-called memory effect, i.e. slowing down the reaction of the electrodes to change the external solution 1, p. 97.

Another source of errors when measuring in dilute solutions is associated with a significant increase in resistance in the contact zone, from the outside of this zone, due to the increase in potassium chloride. If the resistance exceeds the value normalized for the measuring device, then potential measurement errors are possible.

This drawback can be partially eliminated by creating hydrostatic pressure or using special devices 1, p. 105, 106, necessary for measurements under pressure (in autoclaves).

Also known is a reference electrode for potentiometric measurements described in article 3. This reference electrode contains a housing made of dielectric material, a collector electrically connected to a metal electrode fixed inside the housing, immersed in a filling solution of constant composition, including metal ions, from which it is filled electrode. Part of the housing of the reference electrode made of porous Teflon with a thickness of 2 mm, separating a solution of constant composition from the external environment.

Such a design of the reference electrode does not allow us to get rid of the drawbacks indicated by Bbmie — the increase in resistance during measurements in dilute solutions and the memory effect in solutions of ordinary concentrations.

It contains a housing, BbmOjmcHHbrii made of dielectric material, a collector electrically connected to a metal electrode fixed inside the housing, immersed in a solution of constant composition in the housing, including metal ions, from which the metal electrode is embedded, and a polypropylene membrane that separates the solution of constant composition from the external environment. The electrolytic contact in this reference electrode is made through micro-holes in a thin membrane closing a window in the wall of the housing.

The prototype device has the same disadvantages as other analogues.

The purpose of the utility model is to make it possible to set the flow of potassium chloride solution, which is necessary for stabilizing the diffusion potential, decreasing the memory effect and increasing the resistance, regardless of the pressure above the external solution.

This goal is achieved by the fact that in the reference electrode for potentiometric measurements, containing a housing made of dielectric material, a collector electrically connected to a metal electrode fixed inside the housing, immersed in the filling housing a high-grade solution of constant composition, including potassium chloride ions and metal ions, from which is filled with a metal electrode, a membrane attached to the housing that separates a solution of constant composition from the external environment, is made of a dielectric mat rial, whose permeability for water molecules in prevshtaet 50-150 times prorpschaemost polyethylene water molecules, and the resistivity in water nasptsennom state prevshhaet Yu ohm-m, wherein the membrane has a puncture hole.

The membrane can be completely flamed, in particular, from SILRPSON rubber with a thickness of (25-500) -10 m. In this case, the puncture size is 1-3 thick membranes.

The essence of the proposed utility model is illustrated in the drawing, which shows:

3- metal electrode,

4- solution of constant composition,

5- membrane

6- puncture

7- cover

8- crystals of potassium chloride,

9 - salt of the metal from which the electrode 1 is made,

10 measured solution.

a is a view of the membrane 5 in working condition,

b - view of the membrane 5 in storage mode,

C is the thickness of the membrane 5,

d is the size of the puncture 6.

The proposed comparison electrode for potentiometric measurements comprises a housing 1 made of a dielectric material, for example, glass, a collector 2, electrically connected to an electrode 3 mounted inside the housing, made, for example, of silver, zinc or another metal, from which such electrodes are made. The electrode 3 is immersed in the filling housing 1 of a high-grade solution 4 of constant composition, including potassium chloride ions and metal ions, of which the metal electrode 3 is made. The membrane 5 is hermetically attached to the housing 1, for example, using a union nut or by any other known method. The membrane 5 separates the solution 2 of constant composition from the external environment. The membrane 5 is made of a dielectric material, the permeability of which for water molecules is 50-150 times that of polyethylene water molecules, and the resistivity in a water-saturated state is 10 ° Ohm-m, while the membrane 5 has a hole in the form of a puncture 6.

The membrane 5 can be made of various materials that meet the requirements for permeability to water and resistivity in accordance with the essence of the proposed utility model. The best currently known membrane material 5 is silicone rubber. The membrane 5, made of ns silncon rubber, has a thickness of (25-500) -10 m, and the size of the puncture is 1-3 thickness of the membrane. An increase in the thickness of the membrane 5 over 500-10 m leads to an increase in resistance due to dilution of the potassium chloride solution in the outer part of the hole.

The proposed reference electrode works as follows.

When the reference electrode is immersed in the measured solution 10, water molecules move through the membrane 5 in the direction of the gradient of water activity inside the housing 1, regardless of external pressure, dissolve the part of potassium chloride required for filling and create osmotic pressure in the housing 1. The membrane 5 is stretched under pressure, the puncture 6 (view a in the drawing) is expanded and through it a solution of potassium chloride flows into the external environment, which provides electrolytic contact.

Storage of the reference electrode between measurements is possible in a solution with water activity, b; not so close to that of potassium chloride (i.e., not lower than 0.86), then the pressure decreases and puncture 6 closes (type b in the drawing).

Thus, the proposed design makes it possible to set the flow of potassium chloride solution, which is necessary to stabilize the diffusion potential, reduce the memory effect and increase the resistance, regardless of the pressure above the external solution by using the differences in water activity between the internal solution in the reference electrode and the external solution.

The industrial applicability of the useful mode.g1i is determined by the fact that the reference electrode can be made on the basis of the above description and drawings and used to measure the potentials of the electrodes in solutions.

1.Helmuth Galster, pH Measm ement, Weinheim 1990.

2.K.B. Oldham, J.C. Myland, Fundamentals of Electrochemical Science, San Diego, 1994.

3.Satoshi Ito & colab., Talanta 43 (1996), 135-142

Sources of information

Claims (2)

1. A reference electrode for potentiometric measurements, comprising a housing made of a dielectric material, a collector electrically connected to a metal electrode fixed inside the housing, immersed in a saturated housing of constant composition, including potassium chloride ions and metal ions, from which the metal electrode is made, as well as a membrane attached to the housing, separating a solution of constant composition from the external environment, characterized in that the membrane is made of a dielectric mat A series whose permeability for water molecules exceeds 50-150 times the permeability for water molecules of polyethylene, and the resistivity in a water-saturated state exceeds 10 ¹⁰ Ohm • m, while the membrane has a hole in the form of a puncture. 2. The electrode according to claim 1, characterized in that the membrane is made of silicone rubber with a thickness of (25 - 500) • 10 ^-6 m, and the size of the puncture is 1-3 thickness of the membrane.