Summary of the causes of pH meter digital instability
1. Check if the electrodes are damaged;
2. It should be because the electrode has been used for too long. First, calibrate it to see if it is effective;
3. You can try soaking the probe in a 2.5MMOL/L KCl solution;
4. Clean the glass ball, is it possible that some organic matter has adhered to it over time, causing the reaction to be insensitive;
5. There exists a chemical equilibrium in water~CO2+H2O → H++HCO3-. Due to the weak alkalinity of pure water or surface water, this equilibrium shifts towards the positive reaction direction, resulting in a continuous increase in pH. Personally, I think this is the case;
6. Adding neutral salts (such as KCl) as ion strength regulators to the tested water sample can change the total ion strength in the solution, increase conductivity, and make the measurement fast and stable. This method is specified in the national standard GB/T6P04.3-93, which states: "In order to reduce the influence of liquid contact potential and quickly achieve stability when measuring water samples, a drop of neutral 0.1mol/L KCl solution is added to every 50ml of water sample." Although this method changes the ion strength in the water sample to some extent, it has been experimentally proven that this change only changes the pH value by about 0.01pH, which is completely acceptable. However, when using this method, it is important to note that the added Kcl solution should not contain any alkaline or acidic impurities. Therefore, the Kcl reagent should be of high purity, and the water quality of the prepared solution should also be of high purity neutral water quality;
7. During the measurement, CO2 is absorbed and the pH continues to rise;
8. The principle of measuring pH value with a pH meter is to insert an electrode consisting of an indicator electrode and a reference electrode into a solution to form a primary battery. At room temperature (25 ℃), each unit of pH value is equivalent to a change in electromotive force of 59.1mv, which is directly represented by the pH reading on the instrument. The temperature difference is compensated by a device on the instrument. Because pure water has very few ions and cannot form a stable primary battery, neutral salts (such as KCl) are added to the tested water sample as ion strength regulators to change the total ion strength in the solution, increase conductivity, and make the measurement fast and stable;
9. The pH meter reading is unstable: if the measured solution is acidic, use a pH 4 buffer to correct the slope, and if the measured solution is alkaline, use a pH 9 buffer to correct the slope. The closer the pH of the solution with slope adjustment is to the pH value of the measured solution, the better;
10. It may be due to poor contact;
