11 precautions for the preparation, assignment, and management of standard solutions

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11 precautions for the preparation, assignment, and management of standard solutions: The preparation and assignment of standard titration solutions as well as standard solutions used for impurity determination are carried out in accordance with GB/T 601-2016 \"Preparation of standard titration solutions for chemical reagents\" and GB/T 602-2002 \"Preparation of standard solutions for determining impurities in chemical reagents\" (the methods for downloading these standards are provided at the end of the text), as well as the requirements set forth in the method standards regarding the preparation of standard solutions； The number of significant digits of the indication value for the 2 standard solutions shall be retained in accordance with the requirements specified in the certificate or standards ； 3. The containers used for preparing and storing standard solutions should be washed with detergents such as acids, potassium dichromate, or cleaning solutions, and then rinsed repeatedly with distilled water until they are completely clean. The storage container must also be washed several times with this standard solution to prevent changes in its concentration. 4 Before calibration, the prepared solution to be calibrated should be thoroughly mixed; the burette should be washed repeatedly with this solution before filling it with the liquid for calibration. If necessary, blank experiments should also be conducted to rule out the influence of the blank on the standard solution concentration. 5 When directly preparing standard solutions for impurity determination, the reference reagents used must be those suitable for volumetric analysis, and the reference materials should be pre-treated as required for preparing standard solutions, such as by calcination or drying. 6 After calibration, the standard solution should be placed in a reagent bottle that has been pre-washed with the standard solution, sealed, and labeled. 7 The laboratory should use uniform labels that include at least the name of the standard solution, concentration, measurement uncertainty, solvent, preparation date, expiration date, name of the person who prepared it, and the person responsible for storing it. 8 The calibrated standard solutions should be properly stored as required. Generally, standard solutions are stored in sealed, clean reagent bottles; for those with special requirements, the laboratory shall provide the necessary storage conditions in accordance with those requirements. For example, silver nitrate standard solution should be stored in brown reagent bottles because it decomposes easily when exposed to light. For standard solutions with a concentration of 9 < 0.02 mol/L, it is usually necessary to dilute higher-concentration standard solutions using boiled and cooled water before use; when needed, they should be recalibrated to ensure that their readings are accurate and reliable. 10 Standard solutions should be checked regularly; if phenomena such as turbidity, precipitation, or color changes occur during use, it is necessary to determine whether they have deteriorated and to further verify whether re-standardization is required ； 11 Standard solutions should be re-calibrated regularly. The recalibration period for standard titration solutions at room temperature is generally no more than two months. For some special standard solutions, such as hydrochloric acid standard solutions, they must be calibrated before each use.