Summary of reasons for unstable pH meter numbers:
① Check if the electrode is damaged.
② It should be that 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 2.5mmoL/L KCL solution.
④ Clean the glass ball. Has it been too long and there are some organic substances attached to it, causing the reaction to be insensitive.
⑤ There is a chemical equilibrium CO2+H2O → H++HCO3- in water, and due to the weak alkalinity of general pure or surface water, the equilibrium shifts towards a positive reaction direction, resulting in a continuous increase in pH.
⑥ Add neutral salts (such as KCL) as ion strength regulators to the tested water sample to change the total ion strength in the solution, increase conductivity, and ensure rapid and stable measurement. This method is specified in the national standard GB/T6P04.3-93: "In order to reduce the influence of liquid junction potential and quickly achieve stability when measuring water samples, one drop of neutral 0.1mol/LKCL solution is added to every 50ml of water sample." Although this method changes the ion strength in the water sample and causes a change in its pH value to some extent, it has been experimentally proven that this change only changes around 0.01pH in numerical terms, which is completely acceptable. But when using this method, it is important to note that the KCL solution added 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.
How to maintain the pH electrode?
After using the electrode for a period of time, if the slope decreases or the response speed slows down, the following methods can be tried:
① If the measured sample contains protein, the electrode membrane can be cleaned with pepsin/hydrochloric acid wash.
② If the measured sample is an oily/organic liquid, it can be rinsed with acetone or ethanol.
③ If it is found that the electrode solution has become dirty and black, a thiol cleaning solution can be used to clean the solution solution solution.
④ Activate the electrode membrane. Activation method: Soak the electrode regeneration solution for 30 seconds, and then soak it in 3mol/L KCl solution for 5 hours.
