Summary of the reasons for the instability of pH meter
① Check whether the electrode is damaged.
② It should be that the electrode has been used for too long, so calibrate it first to see if it is effective.
③ Try soaking the probe with 2.5mmoL/L KCL solution.
(4) clean the glass ball, isn't it a long time, some organic matter is attached to it, which makes the reaction insensitive.
⑤ There is a chemical equilibrium CO2+H2O→H++HCO3- in water, and the pH will always rise because the equilibrium moves to the positive reaction direction due to the weak alkalinity of ordinary pure water or surface water.
⑥ neutral salt (such as KCL) is added to the water sample to be measured as an ionic strength regulator to change the total ionic strength in the solution, increase the conductivity and make the measurement fast and stable. The national standard GB/T6P04.3-93 stipulates: "In order to reduce the influence of liquid connection potential and quickly achieve stability when measuring water samples, a drop of neutral 0.1moL/LKCL solution is added to every 50ml water sample." Although this method changed the ionic strength in water sample and caused the change of its pH value to a certain extent, the experiment proved that this change only changed the value by about 0.01pH, which was completely acceptable. However, when using this method, it must be noted that the KCL solution added should not contain any alkaline or acidic impurities. Therefore, KCL reagent should be high purity, and the water quality of the prepared solution should also be high purity neutral water quality.
How to maintain pH electrode?
After the electrode is used for a period of time, if it is found that the slope becomes lower and the response speed becomes slower, the following methods can be tried:
① If the measured sample contains protein, the electrode membrane can be cleaned with pepsin/hydrochloric acid lotion.
② If the measured sample is oily/organic liquid, it can be washed with acetone or ethanol.
(3) If the liquid winding part of the electrode is found to be dirty and black, the liquid winding part can be cleaned with mercaptan cleaning 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.
