Reasons for pH meter electrode poisoning
The electrode of a flow reference pH meter relies on the micro osmotic pressure of the electrolyte inside the electrode to form an electrical channel, allowing the electrolyte to penetrate into the measurement solution. When the pressure or concentration of the medium is high, the replenishment channel is not smooth, or there are bubbles present, it may hinder the leakage of the electrolyte, increase the impedance in the middle of the electrical path. If the medium infiltrates back into the pH meter electrode, it may contaminate the salt bridge and even cause chemical reactions with the electrolyte or internal electrode (such as AgCl sulfide → Ag2S), leading to electrode poisoning.
In strongly oxidizing media, the loss of alkaline substances (mainly monovalent cations) in the sensitive glass film can damage the hydration layer and cause poisoning of the pH meter electrode. Acid resistant pH meter electrodes can be selected, and special process measures (special addition of ion formula) are used in the manufacturing process to enhance the anti acid toxicity ability of the glass film. At the same time, the zero potential of the electrode corresponds to pH 0=2, thus correcting the linearity within the acidic range.
The pH meter electrode does not have a good linear relationship outside of pH 2-pH 9, and is prone to the formation of a large number of hydrated hydrogen ions H3O in strongly acidic solutions, resulting in a relative decrease in the number of H on the surface of the pH meter electrode and an increase in pH. Na in strong alkaline medium also participates in the exchange process between H in the solution and H on the electrode hydration layer, resulting in an increase in electrode potential and a decrease in pH value of the pH meter.
