Standard Method for the Preparation of pH Meter Calibration Standards
1)pH4, Potassium hydrogen phthalate standard buffer solution:
Accurately weigh 10.12g of potassium hydrogen phthalate [KHC8H4O4] dried at 115 ± 5 ℃ for 2-3 hours, dissolve and dilute to 1000ml with water.
2)pH7, Phosphate standard buffer solution (pH 7.4):
Accurately weigh 4.303g of anhydrous disodium hydrogen phosphate and 1.179g of potassium dihydrogen phosphate dried at 115 ± 5 ℃ for 2-
3 hours, dissolve and dilute to 1000ml with water.
Additional information: Precisely weigh 3.533g of anhydrous disodium hydrogen phosphate and 3.387g of potassium dihydrogen phosphate dried at 115 ± 5 ℃ for 2-3 hours using phosphate standard buffer solution (pH 6.8), dissolve and dilute to 1000ml with water.
3)pH9, Borax standard buffer solution:
Accurately weigh 3.80g of borax [Na2B4O7 · 10H2O] (note: avoid weathering), add water to dissolve and dilute to 1000ml, place in a polyethylene plastic bottle, seal tightly, and avoid contact with carbon dioxide in the air.
summary
From the current use of pH meters, domestically produced pH meters or acidity meters in China have two types of calibration buffer solutions:
1) The standard solution can be purchased on the market and is usually stored in a sealed polyethylene bottle. It is generally advisable to store standard solutions at room temperature for 1-2 months. When turbidity, mold, or precipitation is observed, they cannot be continued to be used. Store in a refrigerator at 4 ℃, and the used standard solution is not allowed to be poured back.
2) You can also buy buffering agents yourself to configure. But generally, when manufacturers ship, due to national regulations that prohibit the presence of liquids or drugs, only dry pH buffering agents can be included. Customers need to configure them themselves when using them, as long as they dissolve them in deionized water that has been boiled for 15-30 minutes beforehand, and rinse the residual reagents in the reagent bag appropriately. Pour into a 250ml volumetric flask, dilute to the mark, and shake well.
