Standard method for preparing pH meter calibration solutions
1) pH 4, potassium hydrogen phthalate standard buffer:
Precisely weigh 10.12g of potassium hydrogen phthalate [KHC8H4O4] dried at 115±5℃ for 2 to 3 hours, add water to dissolve and dilute to 1000ml.
2) pH7, phosphate standard buffer (pH7.4):
Precisely weigh 4.303g anhydrous disodium hydrogen phosphate and 1.179g potassium dihydrogen phosphate dried at 115±5°C for 2 to 3 hours, add water to dissolve and dilute to 1000ml.
Also added: Phosphate standard buffer (pH 6.8). Precisely weigh 3.533g anhydrous disodium hydrogen phosphate and 3.387g potassium dihydrogen phosphate dried at 115±5℃ 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, place in a polyethylene plastic bottle, seal tightly to avoid contact with carbon dioxide in the air.
Summarize
Judging from the current use of pH meters, domestically produced pH meters or acidimeters in China have two types of calibration buffers:
1) That is, the standard solution can be purchased on the market and is generally stored in a sealed polyethylene bottle. It is generally advisable to store the standard solution for 1 to 2 months at room temperature. If turbidity, mold, or precipitation is found, it cannot be used further. Store in a 4°C refrigerator, and used standard solutions are not allowed to be returned.
2) You can also buy buffer yourself and prepare it later. However, when manufacturers generally ship goods, due to national regulations, some liquids or drugs are not allowed to be shipped, so they can only contain dry pH buffers. Customers need to prepare them themselves when using them. As long as they are dissolved in pre-boiled water for 15 ~30 minutes of deionized water to properly rinse the remaining reagents in the reagent bag. Pour into a 250ml volumetric flask, dilute to volume, and shake well.
