RU164491U1 - DEVICE FOR PH MEASUREMENT WITH IONOSELECTIVE ELECTRODES - Google Patents

Abstract

A device for measuring pH with ion-selective electrodes, comprising a housing with a measuring glass electrode and an auxiliary reference electrode located in it, characterized in that an identical measuring glass electrode located in a sealed container filled with a reference solution having a buffer capacity is used as a reference electrode an auxiliary reference electrode is a porous membrane.

Description

The utility model relates to measuring technique and can be used to measure the pH of various media on standard potentiometric equipment.

A device for measuring the pH of the medium (RU 2100955 C1, IPC A61B 1/005, A61N 1/04, publ. 10.01.1998). The pH probe contains antimony ring measuring electrodes rigidly fixed on thin-walled bushings, a sealed elastic tube stretched over the bushings, a silver-silver reference electrode placed in a non-metallic case with an electrolytic key, and conductors connecting all the electrodes to the connector. The ends of the elastic tube are hermetically connected to the ends of the ring antimony electrodes, and on the working end of the elastic tube there is a tip connected to the sleeve of the end antimony electrode with an elastic tube, while the length of the flexible section of the latter is at least one outer diameter of the tube, and the ratio of the diameter of the tip to the diameter of the elastic tube is 1: 2.

In the pH probe, polymer glue was used to seal the ends of the elastic tube with the ends of the ring antimony electrodes. The tip of the pH probe can be made of non-metallic material and can be either the main or additional housing of the silver chloride reference electrode. The tip can be made of a metal, corrosion-resistant material with a high density, a silver chloride reference electrode can be made in a stand-alone case.

The main disadvantages of the device are the high error (up to 0.1 pH), the need to update the surface of the antimony electrode, the use of silver chloride electrode as a reference electrode. During prolonged operation, its potential changes as a result of a decrease in the concentration of chloride ions in the electrode.

A device is known for changing the pH of solutions (RU 2165615 C1, IPC G01N 27/30, publ. 04/20/2001). The metal oxide pH electrode contains a housing, a metal rod - an electrical conductor, insulating gaskets, an insulating sealant and contact material. The sensitive element is the ion-sensitive outer surface of the body made of metal in the form of a glass, placed in its inner cavity in the center along an axial line, electrically connected to the bottom of the glass using another metal or ion-conducting solution, isolated from its side inner surface by a metal rod - electrical conductor.

The disadvantage of this device is the low measurement accuracy associated with the occurrence of a mixed electrode potential at the metal / solution interface.

Closest to the claimed utility model is a device for measuring the pH of the medium (RU 2112975 C1, IPC 6 G01N 33/04, G01N 27/00, publ. 10.06.1998), which is a stationary pH meter for monitoring liquid media containing a submersible sensor housing a measuring glass electrode, an auxiliary reference electrode and a temperature sensor, and a high-resistance transducer for measuring the EMF of the measuring and auxiliary electrodes. The measuring glass electrode is made of solid electrolyte from an alloy with a hydrogen ion carrier and the auxiliary reference electrode is based on a non-flowing polymer electrolyte, while the electrodes and the temperature sensor are sealed in the housing of the immersion sensor using silicone sealant and a rubber gasket, and the high-resistance converter additionally includes an integrated programmable controller providing automatic reduction of the measured pH values to a temperature of 20 ° C and recalculation of pH values in titratable acidity values.

The disadvantage of this device is the short life of the auxiliary reference electrode, as well as different temperature dependences of the measuring glass electrode and the auxiliary reference electrode, which complicates the process of thermal compensation.

The objective of the utility model is to reduce the error in the measurement of pH, simplify the calibration procedure and increase the service life.

The problem is solved in that the device for determining the pH of the medium contains installed in the housing of the immersion sensor measuring glass electrode and an auxiliary reference electrode. A glass electrode identical to the measuring one, located in a sealed container filled with a standard solution having a buffer capacity, is used as a reference electrode. A porous membrane is located in the reference electrode.

In FIG. 1 is a functional diagram of a device for measuring pH with ion-selective electrodes.

A device for measuring pH with ion-selective electrodes contains a housing 1, with a measuring glass electrode 2 and an auxiliary reference electrode 4. The measuring glass electrode 2 and an auxiliary reference electrode 4 are connected to the secondary measuring transducer 5. The auxiliary reference electrode 4 consists of a glass electrode 3, a sealed container filled with a reference solution 6 having a buffer capacity, and a porous membrane 7. The electrodes are fixed in the housing by sealing elements 8. For determining dividing the pH sensor housing with electrodes embedded therein is placed in the medium to be analyzed 9.

The device operates as follows: when it is immersed in the analyzed medium 9 on the measuring glass electrode 2, a potential arises proportional to the pH value. The reference reference electrode 4 also has potential. Since the glass electrode 3 is placed in a reference solution 6 having a buffer capacity, its potential is constant. The porous membrane eliminates the mixing of the analyzed medium and a standard solution having a buffer capacity.

The potential of the glass electrode is linearly dependent on pH:

,

,

Where:

- стандартный потенциал стеклянного электрода;

- standard potential of a glass electrode;

b = RTln10 / F - coefficient depending on temperature;

pH - pH

Then the potential of the measuring electrode is equal to:

.

.

The potential of the reference electrode is:

.

.

и

совпадают. Таким образом, разность потенциалов индикаторного электрода и электрода сравнения, измеряемая вторичным измерительным преобразователем, определяется следующим соотношением:Since the indicator electrode and the reference electrode are of the same type, then

and

match. Thus, the potential difference of the indicator electrode and the reference electrode, measured by the secondary measuring transducer, is determined by the following ratio:

E = b (pH _environment -pH _reference).

Since the reference solution having a buffer capacity has a known pH, the need to calibrate the electrodes using a series of buffer solutions is eliminated. For example, a phosphate buffer (for example, pH = 6.86), 25-fold dilution of which causes its pH to change by no more than 0.05 units, can be used as a solution with a buffer capacity.

Coefficient b is the only parameter used in the conversion of potential E to pH. The main factor affecting b is the temperature, the influence of which can be taken into account in the secondary transmitter.

Calibration of the device for measuring pH with ion-selective electrodes can be performed at one point. For this, the device is immersed in an analyzed medium with a known pH value and the potential difference between the measuring glass electrode and the auxiliary reference electrode E is measured. Then, the coefficient b is calculated:

In FIG. 2. The calibration characteristic of the dependence of the potential difference between the measuring glass electrode and the reference electrode on the pH of the analyzed medium is presented. For measurements, buffer mixtures are prepared in accordance with GOST 8.135-2004, for the measuring glass electrode and reference electrode, electrodes of the ESLK-01.7 brand are used. According to tests in the pH range from 1.65 to 12.45, the potential difference E between the measuring glass electrode and the reference electrode linearly depends on the pH of the medium being analyzed, with a determination coefficient of 0.9999, which indicates a low measurement error.

Claims (1)

A device for measuring pH with ion-selective electrodes, comprising a housing with a measuring glass electrode and an auxiliary reference electrode located in it, characterized in that an identical measuring glass electrode located in a sealed container filled with a reference solution having a buffer capacity is used as a reference electrode an auxiliary reference electrode is a porous membrane.

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