How to deal with the failure of pH electrode in use

When preparing pH electrodes, rinse them with distilled water before and after measurement. Blot the excess water off the electrode head with a non-hemp swab. Do not wipe, otherwise static electricity will be generated and interfere with the accurate measurement of pH.

pH electrodes will encounter various problems when using, so how do you deal with these problems?

1. The service life of PH electrode?

The guarantee period of the electrode stipulated in the national standard: from the manufacturing date marked on the electrode, within the validity period of one year, when unpacking and using, its performance meets all the requirements of this standard. Within the guarantee period, if the electrode is found to be unable to work normally due to the manufacturer's reasons, the manufacturer shall be responsible for repair or return. It can be seen that the quality guarantee period of the electrode is not used as the premise, the period is one year, so the general life of the electrode is one year, is not correct, the life of the electrode and the use of the environment, for high temperature, strong corrosive places, the life of the electrode will be greatly reduced. For better measurement environment, the service life can reach one to two years.

2. Regular calibration of PH electrode?

For electrochemical meters, the maintenance is generally larger than that of thermal meters. During the use of PH electrodes, the zero point and slope will change. This is because in the process of measurement, the liquid connection is blocked, the glass film is gradually aging, the loss of reference liquid leads to the reduction of chloride concentration, the increase of asymmetric potential and diffusion potential, and so on. Therefore, in order to ensure the measurement accuracy, timely calibration must be carried out. The calibration cycle is usually about a few weeks or even a few months, depending on the site environment. First, test the standard solution that is closer to the measured solution, and determine whether recalibration is necessary according to the error size, but it must be recalibrated under the following circumstances: 1) the electrode base used for a long time and the newly replaced electrode. 2) Measurement of concentrated acid (pH< 2) After, or measurement of concentrated alkali (ph> 12) After. 3) After measuring the solution containing fluoride or the concentrated organic solution. 4) When the temperature of the measured solution is too different from the standard solution temperature (or room temperature).

3. Electrode contamination?

The contamination of the electrode and the formation of the electric channel depend on the micro-osmotic pressure of the electrolyte in the electrode, so that the electrolyte can penetrate into the measurement solution. When the medium pressure or concentration is high and the rehydration channel is not smooth, or there are bubbles, etc., it may hinder the electrolyte exosmosis, increase the electrical path impedance, if the medium reverse infiltration electrode, then pollution salt bridge, and may even have a chemical reaction with the electrolyte or the inner electrode (such as: AgCl+ sulfide →Ag2S) and make the electrode pollution or poisoning.

4. Temperature compensation?

Temperature compensation generally includes three parts: electrode slope temperature compensation, solution temperature compensation, electrode zero temperature compensation; However, the measurement error of solution temperature compensation and electrode zero temperature compensation is very small and can be ignored. Only the electrode slope term (2.303RT/F, Nernst equation) is considered. For every 1℃ temperature increases, the potential will cause a pH change of 0.2mv/per. Represented by pH value, the 1pH value changes to 0.0033pH value every 1℃. That is to say: for the measurement between 20~30℃ and around 7pH, there is no need to compensate the temperature change; For applications where the temperature is >30℃ or<20℃ and="" the="" ph="" is="">8pH or 6pH, the temperature change must be compensated. If the temperature is 50℃ and the PH value is 10, the error is 0.25PH without temperature compensation.

5, Detect and judge the PH electrode is good or bad?

The quality of the electrode is mainly determined by the relevant parameters of the electrode, which are generally zero and slope. For the electrode with zero PH=7.00, the factory standard is generally 95%-- 105%, zero potential: ±20mv; After use for a period of time, the zero point and slope of the electrode will change, but the requirement for the electrode is that the zero point is not more than ±50mv, and the slope is not less than 70%.

6, High pure water PH measurement should pay attention to the problem?

High pure water has weak buffer capacity and poor conductivity, and is prone to pollution and interference. At the same time, in the flow process, static electricity will be generated, affecting the stability and accuracy of measurement. Therefore, low resistance sensitive film electrode must be used in the measurement of pure water. There are few ions in high purity water and the diffusion potential is unstable. Therefore, the distance between the reference electrode and the measuring electrode should be avoided as far as possible in PH measurement, so as to reduce the impedance between the two electrodes. The spherical composite electrode must be used. The flow velocity has a great influence on the measurement of high pure water. If the flow velocity is not stable, it will lead to the instability of liquid connection potential and flow diffusion potential. Therefore, the flow velocity range must be guaranteed during the measurement.

7. Requirements for high temperature PH electrodes?

The high temperature of the medium solution is generally above 100℃. Under such conditions, the erosion effect of the solution on the glass electrode is particularly serious, especially in the alkaline pH range is more intense. This erosion effect causes the potential drift of the glass electrode and the electrode performance deteriorates. Therefore, high temperature pH measurement should first solve the corrosion resistance of the electrode. In the pharmaceutical, fermentation, food and other industries of microbial breeding tank, pH measurement requires that the glass electrode can withstand the high temperature of 120-130 ℃, that is, the electrode can withstand the erosion of high temperature solution. Therefore, high temperature electrode is generally required to enhance the mechanical strength and corrosion resistance of glass film, the use of special glass film can meet the requirements.