Benefits of our electrodes

 

In the absence of interfering ions, most glass pH electrodes have a linear function up to pH = 14.Gomel Plant of Measuring Equipment was organized in the USSR in 1958 as a leading enterprise specializing in production of analytical devices for monitoring and process control, environmental monitoring, and electrode systems for potentiometric measurements.
At present, our company is the only enterprise instrument-making industry of the Republic of Belarus, specializing in the production of these products.
Republican Unitary Enterprise Gomel plant instrumentation design, fabrication of electrodes for potentiometric measurements over 50 years.
In potentiometric (electrometric) method for determining the activity of ions in solution is required electrode system consisting of two electrodes:
        measurement (glass) electrode, which is immersed in the test solution, the change of which affects the potential of the electrode,
        auxiliary electrode (comparison) with permanent potential.
The theory of building on the example of a glass electrode in determining the activity of hydrogen ions.
Glass (measuring) electrode - a system that includes a small vessel of glass placed in a buffer solution and internal shunts. Vessel has a neck made ​​of insulating glass, which is soldered to the end of the ball (disc) of special glass electrode, which has a significant electrical conductivity. Shunts can serve as an internal silver chloride electrode. Glass conducts electricity because it can migrate alkali metal ions (sodium or lithium), which are a part in its synthesis.
On the border of shunts (internal silver chloride electrode) and an internal buffer occurs quite some potential. Potential is generated and the border membrane glass with internal solution. During the measurement of the internal solution, and hence the sum of the internal potential remain constant.
The origin of the glass electrode potential can be represented as follows. When the electrode is placed into the solution, the surface layers of the glass electrode from the test solution rapidly penetrate the hydrogen ions, forcing the ions contained in the glass of the alkali metal. Energy state of the ions in the glass and the solution is different. This leads to the fact that hydrogen ions are so divided between the glass and the solution that the surfaces of these media (phases) acquire opposite charges and between the glass and the analyte solution potential difference. The magnitude of this potential difference depends on the pH, because the tendency of hydrogen ions to pass into the glass depends on their concentration in the solution. The larger it is, the greater is the desire. Potential difference so directed that it reduces the tendency of hydrogen ions to pass into the glass. At a certain concentration of hydrogen ions in the solution between the desire to move into the glass and electric forces that have to be overcome, equilibrium is established. The transition of H + ions from the solution in the glass will be the same rate as the reverse transition from the glass to the solution.
To measure the potential of the glass electrode uses an auxiliary electrode (comparison).
Potential auxiliary electrode in measuring the pH remains virtually unchanged since it depends on the concentration of chloride ions, which is about the system Ag / AgCL (if silver chloride electrode) is defined and remains constant. The auxiliary electrode is connected to the analyzed solution electrolytically key with a solution of potassium chloride. The role of this key - ensure that the current between the test solution and the auxiliary electrode to stabilize and minimize the potential at this boundary.
Graphically, the dependence of the emf electrode system consisting of a glass and auxiliary electrodes, the pH is a straight line (Figure 1).
In very acidic solutions can be observed "acid error" in a very alkaline - "alkaline error", ie curve deviates from the linear behavior. The position of these deviations depend on the glass composition and the nature of the ions.
The curve of the emf the pH value of a point (area), corresponding to a concentration of the ion, in which the electrode potential is independent of temperature. This isopotential point (Figure 1).

 

 

 

 

Figure 1. A plot of the emf electrode system of the pH value
The equation of this line (Nernst)

 

Е = Е0 + S? lg a, (1)

where
E - the potential difference between the measurement (glass) electrode and the auxiliary electrode mV;
0 - constant that depends largely on the properties of the electrode (standard electrode potential), mV;
S - slope of the electrode function of the electrode (Nernst slope of the)

 

(2)

where
R - gas constant, J? Mol -1? K-1;
n - ion charge because of its mark;
F - the Faraday, C / mol;
N - is the absolute temperature, º K;
a - activity of the corresponding ion.
Nernst equation for pH measurement can be written as

Е = Еи + St (рНt рНи), (3)

where
Eu, IDH - nominal values ​​of the coordinates of the isopotential point of the electrode system consisting of a glass (measuring) and auxiliary electrodes, respectively, mV, pH;
pH t - pH buffer solution at t, º C;
t - slope characteristics of hydrogen in mV / pH at t º C, calculated using the formula

(4)

where
t - temperature of the analyzed medium, º C;
n - ion charge.
The slope of the electrode system t depends on the temperature at 25 º C and a ten-fold change in the activity of the ion is determined it is 59.16 mV for singly charged ions, and 29.56 for the doubly charged ions. Usually, however, the slope of the electrode function is less than the theoretical value due to the presence of impurities or preventing aging liquid electrode.
For the convenience of assessing the actual slope of the electrode system S t real, as a rule, use the dimensionless ratio By S, taking into account the deviation of the real value of the slope of the theoretical value;

 

(5)

where
t the real - the real value of the slope of the electrode function, mV / pH;
t - the theoretical value of the slope of the electrode function, calculated by formula (4), mV / pH.
K factor S, mostly of 0.8 ... 1.2, allows the deviation of the slope of the electrode system t real from the theoretical value.
Plant started its activities with the issuance of common electrodes
not sealed design (Figure 2) for the measurement of pH in a narrow range.

Figure 2. Electrode is sealed design
In glass electrodes are not sealed design, particularly at temperature analyzed environment, can be broken seal, the internal buffer interacts not only with the glass body of the electrode, but also, and other materials that provide a seal (rubber, resin, etc.). As a result of this internal solution changes its composition, which leads to a rapid change of control of the electrode potential and change the coordinates of the isopotential point.

Currently, we are producing more sophisticated glass electrodes sealed construction is not only to measure the pH value in a wide range from 0.5 to 14 pH, but also for the measurement of other ions.
 
Our factory is the only company in the former Soviet Union, producing electrodes sealed construction.

 

 

 Figure 3. Electrode sealed design

 
Advantages of electrodes sealed design (Figure 3). Internal buffer, filling the electrode body is in a sealed glass tube, it is not in contact with any other materials, except glass, and therefore maintains its structure even during sudden temperature changes of the analyzed medium, resulting in long-term potential of the electrode remains almost unchanged that has a positive effect on the performance of the electrodes.
Gomel Plant instrumentation produces electrodes for potentiometric measurements as measurement (glass, membrane, Redox) and secondary (comparison).
 
For the measurement of pH, we suggest using our electrodes:
in the laboratory:
- Electrodes sealed design ESL-43-07, ECL-43-07SR, ECL-45-11 for temperatures from 0 to 40 º C;
- Electrodes sealed design ECL-63-07, ECL-63-07SR, ECL-15-11 for temperatures from 25 to 100 º C;
- Combined glass laboratory electrodes ESKL-08M.1, ESKL-08M for temperatures from 0 to 50 º C, the change in the diffusion potential electrolytic key auxiliary electrode in the electrode transfer from the acid to alkaline is ± 1 V;

in an industrial environment:
- Electrodes sealed design ESP-04-14 for temperatures from 0 to 40 º C;
- Electrodes sealed design ESP-01-14 for temperatures from 25 to 100 º C;
- Electrode design sealed ESP-31-06 for temperatures from 70 to 150 º C;
- Electrode sealed design of EC-71-11 - sterilizable, range of pH 0.5 to pH 12 at 25 º C (electrode without sterilization can be used for temperatures from 15 to 80 º C). Glass electrode used for the manufacture of the electrode ES-71-11, allows measurements in solutions with pH to -0.5 pH (in solutions containing sulfuric acid);
special electrodes:
- Electrode 5M2.840.019 sealed design - AN-72529/60 analyzers,
- Electrode 5M2.840.074 sealed design - for AS-7932 analyzer.
We also have glass ion-selective electrodes:
- Glass electrode ESL-51-07, ECL-51-07SR sealed design - to measure the activity concentration of sodium ions Na + and silver ions Ag +,
- Glass electrode ES-10-07 sealed design - to measure the activity concentration of sodium ions Na +, with the apparatus of the p and N-205measures the active concentration of sodium ions in a chemically demineralized water and condensate steam pressure boilers;
- Electrode sulfidserebryany ESS-01 - for the determination of sulfide ion S -2 in industrial conditions, including liquors of sulfate pulp and paper production, and also to measure the activity concentration of silver ions Ag +,
and ion-selective membrane electrodes:
- Electrode argentitovy EA-2 - to measure the activity of sulfide ions (of p S) and can be used in industrial sensors for automatic control of the concentration of sulfide ions p S in aqueous solution, is used in the programs our Signaling SC-2,
- Membrane electrode EM-I -01, EM-I-01SR - to measure the activity concentration of ions I -,
-   membrane electrodes EM-CN -01, EM-CN-01SR - to measure the activity concentration of the ion CN -; may be used in the chemical and mining industry, the analysis and purification of wastewater from electroplating facilities for enrichment plants in the flotation process using cyanide salts , is used in the programs our Signaling CX-2,
- Membrane electrode EM-Cl -01, EM-Cl-01SR - to measure the concentration of the active ions Cl; may be used in the chemical industry for the control of technological processes in the analysis and purification of wastewater from electroplating facilities, scientific research, medicine,
-   membrane electrodes EM-NO 3 -07, EM-NO 3-07SR - to measure the activity concentration of the ion NO - 3, can be used for soil analysis, crop production, food processing, can be used in laboratories in various industries, biology, medicine, environmental protection,
F or the measurement of redox potentials produce electrodes as with the use of precious metals and special glass electrode: EPV-1, EPV-1SR, ETP-02, EPL-02, EC-01.
Electrodes EPV-1, EPV-1SR, EPL-02 are the most common electrodes. In the reversible redox systems allow determination of the concentrations of components to 10 -5 N. In comparison with the electrode ETP-02 are less sensitive to impurities and long service life, especially at elevated temperatures and in media containing solids. However, gaseous oxygen and hydrogen, catalyst poisons affect the electrode potential. The electrodes are limited in scale oxidation potentials, especially in environments with low oxidation potentials due to a reversible system H 2 / H + on platinum.
ETP-02 electrode has high sensitivity and low polarizability due to the fact that the indicator portion is made ​​of fine platinum. This allows, in some cases a measurement solutions malobufernyh systems. The high sensitivity of the electrode due to the activity of fine platinum to hydrogen and oxygen, as well as to poisons (sulfur, arsenic, mercury) limits its use in dilute solutions and solutions containing hydrogen and oxygen catalyst poisons.
Electrode EO-01 (with an electron-conducting glass electrode) in most solutions of reversible redox systems have less current exchange than the platinum wire. As the electrodes EPV-1, EC-electrode 01 is, the determination of concentrations in reversible systems down to kontsentratsiy10 -5 N, but the time of establishing equilibrium potentials of several more. Electrode EO buy 01 not specific catalytic effects, not an effect of gaseous oxygen and hydrogen.Electrode enables measurements in solutions with mild redox properties (in solutions with relatively low buffer capacity). Because of the relatively low chemical stability of the glass electrode is limited by the scope of the electrode EO-01 pH (from 3 to 11 pH with direct potentiometric measurements).
Benefits of our glass electrodes.
Measuring glass electrodes with an inner filling - sealed design, the benefits of a sealed electrode design discussed earlier.
In addition, to exclude the effects of static electricity on high-resistance readings of the measuring laboratory electrodes: ESL-43-07, ECL-43-07SR,
ESL-63-07, ECL-63-07SR, ECL-45-11, ESL-15-11, ECL-51-07, ECL-51-07SR, ES-10-07 and ESP-31-06 ES-71-11, we use not only silent shielded coaxial cable with insulation resistance of more than 10 12 ohms, but shielding the inside of the electrode metal shield that reduces drift potential.
In the operational documents, we specify a linear range of the ion characteristics of the electrodes not only for the temperature of 25 º C (20 º C), but for the maximum temperatures of the analyzed medium (with state standards), which allows the consumer to choose necessary for their conditions electrode, while the other manufacturers normalized linear range of ionic data for a temperature of 25 º C.
The regulatory and operational documents to the measuring electrode, we specify the optimal temperature ranges for the analyzed environment and span that allows the consumer to choose the electrode for the continued operation of the electrodes without compromising their performance.
For all glass pH - electrodes interfering ions are alkali metal ions - mostly sodium ion, so we normalize the top of the linear range of the hydrogen characteristic pH-electrodes with the interference of sodium ions of 0.1 mol / l (with state standards).
In the absence of interfering ions, most glass pH electrodes have a linear function up to pH = 14