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 of CO2+H2O → H++HCO3- in water, and due to the weak alkalinity of general pure water or surface water, this equilibrium shifts towards the positive reaction direction, resulting in a continuous increase in pH.
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 neutral 0.1mol/LKCL 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, KCL reagents should be of high purity, and the water quality of the prepared solution should also be of high purity neutral water quality.
