pH meter is an indispensable instrument in the field of electrochemical analysis, which is widely used in environmental monitoring, food testing, biomedical research and other fields. It can directly reflect the content and quality factors of the constituent elements of the measured substance, and the accuracy of its measurement results is crucial for scientific research and practical application. The pH meter is mainly composed of two parts: electrode and electrometer, in which the quality of the electrode directly determines the accuracy of pH value and other parameters in the readout value. Therefore, it is of great significance to detect electrode aging in time and correct the parameters to ensure the accurate measurement of pH meters.
Measuring principle
The pH value is measured by a chemical sensor, an electrode, which converts the pH value in the solution into electricity, which is then amplified, adjusted, and read out by the display circuit. This measurement method is known in analytical chemistry as transient metamorphosis analysis, i.e., both the electrode and the solution are stationary, the concentration gradient on the electrode surface is time-dependent, and the electrode's response signal is dependent on the chemical composition of the solution attached to its surface. In terms of measurement principle, the electrode response signal can be regarded as an autoactive battery, where the pH measuring electrode is an electrochemical half-cell and the other electrochemical half-cell is a reference electrode.
Analysis of the causes of errors
Measure the effect of electrode potential
The stability of the measured electrode potential depends mainly on the chemical state and physical properties of the electrode surface. The glass electrode is a commonly used pH measurement electrode, which has good versatility and does not involve an electron exchange process, and is a hydrogen ion electrode that is not affected by oxidants and reducing agents. However, when the glass electrode is first immersed in an aqueous medium, it forms a hydrated (outer) layer, which expands the glass film. The rate at which the hydrate dissolves depends on the composition of the glass and the properties of the sample solution, which determines the lifetime of the electrode. Therefore, the ambient temperature has a great influence on the measuring electrode, and the use of different measuring electrodes at different temperatures for different solutions can reduce the reading error of the measuring electrode and prolong the service life of the electrode. In addition, contamination of the glass film can also lead to a failure to reach a fast equilibrium between the electrode and the solution, which can affect the accuracy of the measurement results.
Effect of reference electrode potential
The potential of the reference electrode is generally considered to be constant, but in reality it can also be affected by some factors. For example, a change in the concentration of the electrolyte solution in the reference electrode, a change in the physical state of the electrode, etc., can cause fluctuations in the potential of the reference electrode. Therefore, choosing the right reference electrode and keeping it in good working order is essential to improve the accuracy of pH measurements.
Effect of junction potential of liquids
Liquid junction potential refers to the potential difference that is formed between two different solutions. In pH measurements, the magnitude and stability of the liquid junction potential also affect the measurement results. The generation of liquid junction potential is mainly due to the diffusion and migration of ions in the solution, and its magnitude is related to the concentration of the solution, ion type, temperature and other factors. In order to reduce the effect of the junction potential of the liquid, it is usually necessary to make the filled solution as an isomobility solution as much as possible, and the difference error should be less than 5%. At the same time, it is necessary to avoid the quality of the solution due to contamination and leakage of the liquid.
Error correction method
(1) Experimental screening
Through experimental screening, it was found that the reading error of the old and new electrodes in different solutions was related to the solution temperature. For example, a pair of new electrodes and an old electrode that had been used for 11 months were placed in a borax solution to measure the pH and found that the reading error of the old and new electrodes was about 0.5 pH. This indicates that the aging degree of the electrode has a great influence on the measurement results, so it is necessary to detect the aging of the electrode in time and correct the parameters.
(2) Application of intelligent control technology
With the continuous development of microcontroller technology, it has become an effective means to apply it to error correction in pH meters. Process monitoring with a microcontroller system enables measurement and compensation tasks to be completed automatically and accurately. First of all, the simulation and debugging of the relevant software modules are completed through the host computer, and then the microcontroller software that has been debugged is downloaded to the intelligent module of the pH meter through the RS-232 serial interface, so that the instrument is transformed into a portable intelligent pH meter. The user can interact with the LCD display by touching the keys, and the instrument can prompt the measurement operation steps, display the measurement results, and automatically complete the error compensation.
conclusion
Based on the in-depth analysis of the causes of pH meter errors, combined with the application of experimental screening and intelligent control technology, an improved pH meter error correction method is proposed. This improved pH meter combines intelligent control with traditional measurement technology, avoids the adverse effects of various interference measurement parameters, and improves the ability of automatic measurement and effective error compensation. It not only improves the measurement accuracy and reliability of pH meters, but also proposes a new method to implement integrated technologies in applied chemistry, electronics and microcomputer applications. In future research, other advanced sensor technologies and signal processing methods can be further explored to further improve the performance and application range of pH meters.
