Summary of the reasons for the digital instability of the pH meter:
① Check whether the electrodes are damaged.
②It should be that the electrode has been used for too long, first calibrate to see if it is effective.
③ You can try soaking the probe with 2.5mmoL/L KCL solution.
④ Clean the glass ball, is it a long time, some organic matter is attached to it, resulting in insensitive reaction.
⑤There is a chemical level CO2 + H2O→H+ + HCO3- in water, and the pH will always rise because the balance moves to the positive reaction direction because the general pure water or surface water is weakly alkaline.
⑥Add a neutral salt (such as KCL) to the water sample to be tested as an ionic strength regulator to change the total ionic strength in the solution, increase the conductivity, and make the measurement fast and stable. This method stipulates 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, add a drop of neutral 0.1moL/LKCL solution to every 50ml water sample." Although this method Changing the ionic strength in the water sample caused a change in its pH value to a certain extent, but it was proved by experiments that this change only changed about 0.01pH in value, which is completely acceptable. However, when using this method, it must be noted 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 solution should also be high-purity neutral water.
How to maintain the pH electrode?
After using the electrode for a period of time, if you find that the slope becomes lower and the response speed becomes slower, you can try the following methods:
① If the measured sample contains protein, the electrode membrane can be cleaned with pepsin/hydrochloric acid washing solution.
② If the measured sample is oily/organic liquid, it can be rinsed with acetone or ethanol.
③ If the junction of the electrode is found to be dirty and black, the junction can be cleaned with mercaptan cleaning solution.
④ Activate the electrode membrane. Activation method: soak in electrode regeneration solution for 30 seconds, then soak in 3mol/L KCl solution for 5 hours.
