(1) The electrode bulb and liquid junction are contaminated, and the dirt can be carefully removed with a fine brush, cotton ball or toothpick. The protective cover on the head of some plastic shell pH electrodes can be unscrewed, which makes cleaning more convenient. If the pollution is serious, you can use detergent to clean it according to the previous method.

(2) The external reference solution is polluted. For the rechargeable electrode, you can prepare a new KCl solution and add it. Note that it must be poured out when adding it for the first and second time, so as to clean the inner cavity of the electrode.

(3) Aging of the glass sensitive film: Soak the electrode bulb with 0.1mol/L dilute hydrochloric acid for 24 hours. Rinse with pure water, then soak in electrode soaking solution for 24 hours. If the passivation is serious, you can also soak the lower end of the electrode in 4% hydrofluoric acid solution for 3 to 5 seconds (solution preparation: 4ml hydrofluoric acid diluted with pure water to 100m1), wash it with pure water, and then put it on the electrode. Soak in the soaking solution for 24 hours to restore its properties.

1. pH4, Potassium Hydrogen Phthalate Standard Buffer:
Accurately weigh 10.12g of potassium hydrogen phthalate [KHC8H4O4] dried at 115±5 degree for 2 to 3 hours, add water to dissolve and dilute to 1000ml.

2. pH7, phosphate standard buffer solution (pH7.4):
Accurately weigh 4.303 g of anhydrous disodium hydrogen phosphate and 1.179 g of potassium dihydrogen phosphate, which were dried at 115±5 degree for 2 to 3 hours, add water to dissolve and dilute to 1000 ml.
Additional supplement: Phosphate standard buffer solution (pH6.8) Accurately weigh 3.533g of anhydrous disodium hydrogen phosphate and 3.387g of potassium dihydrogen phosphate, dried at 115±5 degree for 2 to 3 hours, add water to dissolve and dilute to 1000ml .

3. pH9, borax standard buffer:
Precisely weigh 3.80g of borax [Na2B4O7·10H2O] (note: avoid weathering), add water to dissolve and dilute to 1000ml, put it in a polyethylene plastic bottle, seal it tightly, and avoid contact with carbon dioxide in the air.