Lead acetate method for the detection of amino acids

1. Experimental principle
Amino acids can react with specific reagents to produce unique phenomena for identification. Lead acetate interacts with amino acids under specific conditions, which can show characteristic changes that can be used to judge the presence or absence of amino acids. This is based on the chemical interaction between specific functional groups of amino acids and lead ions and other components in lead acetate, which in turn produces obvious phenomena such as precipitation and color change, which can be used as the basis for the detection of amino acids.

2. Experimental materials
1. ** Reagents **: lead acetate solution, which needs to be precisely configured at a certain concentration to ensure the accuracy of the experiment; various known amino acid standards are used for controlled experiments; unknown samples, that is, samples to be detected for amino acids.
2. ** Instrument **: several clean test tubes for carrying the reaction liquid; dropper, accurate absorption and drip addition of reagents; constant temperature water bath pot, control the reaction temperature, so that the reaction can be carried out in a suitable environment.

III. Experimental steps
1. ** Preparation stage **
- Take an appropriate amount of known amino acid standard solutions in different clean test tubes, and mark them clearly as a positive control. For example, take glycine, alanine and other standard solutions of 2mL each in the corresponding test tube.
- Take an appropriate amount of unknown sample in another clean test tube and mark them well.
2. ** REACTION STAGE **
- Use a dropper to add lead acetate solution dropwise to a test tube containing a known amino acid standard solution and an unknown sample test tube. Shake while adding dropwise. Pay attention to observe the change of the solution. Generally add 5 - 8 drops of lead acetate solution dropwise to ensure that the reaction is sufficient.
- Put all the test tubes into a constant temperature water bath, set a suitable temperature, such as 37 ° C, and react for 10 - 15 minutes to make the reaction reach a stable state.
3. ** Observation Record **
- After the reaction is over, take out the test tubes, observe and record the phenomenon of the solution in each test tube. In the positive control, if amino acids react with lead acetate, there may be characteristic phenomena such as white precipitation or solution color change. Compare the positive control to observe whether similar phenomena occur in the test tube of the unknown sample. If similar precipitation or color change occurs, it is preliminarily inferred that the unknown sample may contain amino acids; if there is no obvious change, it may not contain amino acids.

4. Precautions
1. During the experiment, the dropper should be cleaned in time after use to prevent cross-contamination of different reagents and affect the accuracy of the experimental results.
2. Lead acetate solution has a certain toxicity, and care should be taken during operation to avoid contact with the skin and accidental ingestion. If it is inadvertently touched, rinse with plenty of water immediately and seek medical attention in time.
3. The temperature of the constant temperature water bath needs to be strictly controlled. Excessive or too low temperature may lead to abnormal reactions and affect the judgment of experimental results.