Preparation of ammonium acetate buffer (pH7)
1. Required materials
1. Ammonium acetate (analytical purity)
2. Acetic acid (analytical purity)
3. Sodium hydroxide (analytical purity)
4. Ultrapure water
5. pH meter

2. Preparation steps
1. Accurately weigh an appropriate amount of ammonium acetate and place it in a clean beaker. According to the theoretical calculation, the amount of ammonium acetate is determined according to the concentration and volume of the required buffer. For example, to prepare 1L of ammonium acetate buffer with a concentration of 0.1mol/L, it is necessary to accurately weigh the ammonium acetate solid (the molar mass of ammonium acetate is about 77.08g/mol) $0.1mol/L × 1L × 77.08g/mol = 7.708g $.
2. Add an appropriate amount of ultrapure water to the beaker containing ammonium acetate and stir with a glass rod to promote the full dissolution of ammonium acetate. This process needs to ensure that the ammonium acetate is completely dissolved and there is no solid residue to ensure the accuracy of the buffer concentration.
3. Calibrate the pH meter to ensure the accuracy of the measurement data. After the calibration is completed, insert the electrode of the pH meter into the solution in which the ammonium acetate has been dissolved.
4. Slowly add acetic acid or sodium hydroxide solution dropwise, while closely observing the pH meter. If the pH value of the solution is higher than 7, add acetic acid solution dropwise for adjustment; if the pH value is lower than 7, add sodium hydroxide solution dropwise for adjustment. During the adjustment process, stir while adding dropwise to make the solution fully mixed until the pH meter number stabilizes at 7.00.
5. Transfer the pH-adjusted solution to a suitable volume volumetric flask, rinse the beaker and glass rod with ultrapure water several times, and transfer the rinsing liquid to the volumetric flask together, then bandwidth evaluation to the required volume, fully shake well. For example, if 1L buffer is prepared, bandwidth evaluation to the 1L scale line.
6. Transfer the prepared ammonium acetate buffer (pH7) to a clean, dry and well-sealed reagent bottle and label it with key information such as the name of the buffer, pH value, and preparation date.

III. Precautions
1. The reagents used must be of analytical purity level to ensure the purity and quality of the buffer.
2. In the process of adjusting the pH value, the dripping speed should be slow to avoid excessive pH adjustment, resulting in the buffer not meeting the requirements.
3. Solution transfer and bandwidth evaluation operations need to be standardized to ensure the accuracy of buffer concentration.
4. After the preparation is completed, the buffer should be used as soon as possible. If it needs to be stored, it should be placed in a suitable temperature environment to prevent the deterioration of the buffer from affecting the use effect.