In the determination of sample content, many analytical methods need to use standard solution, and the standard solution is reflected by the standard concentration, the accuracy of the standard solution concentration directly affects the result of sample determination. The following is a small edition of Bolinda to share with you the precautions for preparing standard solutions.

Precautions for preparing standard solution:

1. The solution used in the analysis experiment should be prepared with pure water, and the container should be washed three times with pure water. Solutions with special requirements should be tested for blank values of pure water in advance. If AgNO3 solution is prepared, the water should be tested for the absence of CIˉ, and the solution prepared for EDTA coordination titration should be tested for the absence of impurity cations.

2, the solution should be filled with reagent bottles with plugs, the solution that is easy to decompose in light should be installed in brown bottles, the solution that is prepared with volatile reagents such as organic solvents, the bottle stopper should be tight, the solution that is easy to prepare and release corrosive gases should also be capped tightly, and the solution should be sealed with wax when stored for a long time. Concentrated lye should be used in plastic bottles, such as in glass bottles, with rubber plugs, not with glass grinding head plugs.

3, each bottle of reagent solution must have a label indicating the name, specification, concentration and preparation date.

4, the solution storage may have deterioration reasons:

Glass with water and reagents will be more or less eroded (especially alkaline solution), so that the solution contains sodium, calcium, silicate and other impurities. Some ions are adsorbed on the glass surface, which cannot be ignored for low concentration ion standard solution. Therefore, ionic solutions below 1mg/mL cannot be stored for a long time.

Due to poor sealing of the reagent bottle, CO2, O2, NH3 or acid fog intrusion in the air changes the solution, for example, ammonia absorbs CO2 to form NH4HCO3, KI solution is easily oxidized by oxygen in the air to form I2 in the light and becomes yellow, and reducing agent solutions such as SnCL2, FeSO4 and Na2SO3 are easily oxidized.

Some solutions see photodecomposition, such as silver nitrate, mercury salts, etc. Some solutions are gradually hydrolyzed after being placed for a long time, such as bismuth salt and antimony salt. Na2SO3 can also be gradually reduced by microbial action.

Some coordination titrations indicate that polymerization and oxidation reactions occur after the solution is placed for a long time, and can not be sensitive to indicate the end point, such as chromium T, xylenol orange, etc.

Due to the volatilization of volatile components, it is attempted to reduce, resulting in abnormal phenomena in the experiment.

5. When preparing sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and other solutions, the acid should be poured into the water. For reagents that release more heat during dissolution, they should not be prepared in reagent bottles to avoid bursting. When preparing sulfuric acid solution, sulfuric acid should be divided into small portions into water, stirring while adding, and cooling the outer wall of the beaker with cold water if necessary.

6, when preparing the solution with organic solvents, sometimes organic matter dissolved slowly, should be stirred from time to time, you can warm the solution in a hot bath, can not be directly heated. Easy ene solvent should be used away from open flame. Almost all organic solvents are toxic and should be operated in the fume hood, unnecessary evaporation of organic solutions should be avoided, and the beaker is capped.

7, to be familiar with some commonly used solution preparation methods. If the iodine solution should be dissolved in a concentrated potassium iodide solution, it can be diluted. The aqueous solution of readily hydrolyzed salts should be dissolved with an acid solution first, and then diluted with a certain concentration of dilute acid.

8. Do not touch corrosive and highly toxic solutions with your hands. Highly toxic waste liquid should be detoxification treatment, can not be directly poured into the sewer.

The above content is an introduction to the precautions for the preparation of standard solution, standard solution is a titration solution commonly used in capacity analysis, by which the content of the substance to be measured is measured, by which the concentration of the unknown solution is obtained.