What are the precautions for the determination of acetic acid moisture by the Karl Fischer method?

What are the precautions for the determination of acetic acid moisture by the Karl Fischer method?

Karl Fischer method is a classical volumetric analysis method for the determination of moisture content in substances, which is widely used in chemical, pharmaceutical, food and other fields. In the determination of acetic acid moisture, Karl Fischer method is widely used because of its high sensitivity and accuracy. Some key points need to be paid attention to during the experiment to ensure the accuracy and reliability of the measurement results. This paper will analyze in detail the matters needing attention in the determination of acetic acid moisture by Karl Fischer method.

The Principle and Reagent Preparation of 1. Karl Fischer Method

the Karl Fischer method is based on the principle of the reaction of iodine with sulfur dioxide with moisture in the presence of pyridine. The reaction is as follows:

$$ I2 SO2 Py \xrightarrow{H2O} 2HI SO_2 \cdot Py $$

in this reaction, moisture reacts with iodine, resulting in the consumption of iodine in proportion to the water content. Therefore, in the process of determination, it is necessary to accurately prepare the Fischer reagent (iodine-sulfur dioxide-pyridine solution) and ensure the accuracy and stability of its concentration.

Note:

1. accuracy of reagent preparation: The preparation of Fischer reagent should be strictly in proportion to avoid deviation of determination results due to inaccurate reagent concentration.
2. Preservation conditions of reagents: Fischer reagent should be kept away from light and moisture to prevent the influence of moisture and oxygen in the air on its performance. Generally, Fischer reagents should be stored in a closed container and placed in a cool, dry place.
3. Validity period of reagent: Due to the failure of Fischer reagent due to environmental factors, it is necessary to replace the reagent regularly and confirm its activity before each use.

2. Sample Pretreatment and Titration Operation

in the determination of acetic acid moisture, the sample pretreatment and titration operation directly affect the accuracy of the determination results.

Note:

1. representativeness of samples when sampling, ensure the representativeness of the sample and avoid the deviation of the results due to uneven sampling.
2. Drying of samples: Before titration, the sample should be fully dissolved, and avoid containing other volatile substances in the sample, so as not to interfere with the determination.
3. Control of the titration process: Feisal reagent should be added slowly during titration to observe the change of end point. Typically, the end point is judged by the change of the solution from red to colorless, taking care to avoid the addition of excess reagent.

Calibration and Maintenance of 3. Instruments

the results of the Karl Fischer method depend on the accuracy and stability of the instrument. Therefore, the calibration and maintenance of the instrument is the key to ensure the accuracy of the measurement.

Note:

1. calibration of the burette the burette needs to be calibrated regularly to ensure the accuracy of its volume measurement. It is recommended to use the standard solution for verification.
2. Maintenance of Moisture Analyzer the instrument should be cleaned and maintained regularly, especially the titration head and pipeline part, to prevent sample residue or reagent crystallization from affecting the determination.
3. The accuracy of the balance: Sample weighing requires the use of a high-precision balance to ensure the accuracy of the weighing.

4. the influence of environmental factors

the experimental environment is also an important factor affecting the results of the Karl Fischer method, especially the interference of temperature and humidity on the experiment.

Note:

1. temperature and humidity control in laboratory during the experiment, the temperature and humidity of the laboratory should be controlled to avoid the influence of the external environment on the reagents and samples.
2. Anti-vibration and dust-proof of the test bench: The test bench should be far away from vibration source and dust source to prevent external interference from affecting the titration results.
3. Light-proof preservation of reagents reagents and samples should avoid direct sunlight to prevent chemical reactions caused by light.

5. common problems and solutions

in the actual measurement process, some problems may be encountered, such as the end point is not obvious, the measurement results are high or low.

Note:

1. the end point is not obvious: May be due to reagent failure or impure sample. At this point, the reagent needs to be reconstituted and the sample quality checked.
2. High results: This may be due to the presence of other volatile substances in the sample or the expiration of the reagent. Re-test the sample and confirm the validity of the reagent.
3. Determination results are low: May be due to insufficient reagent or improper operation during titration. Reagent preparation and titration operations need to be checked for specification.

6. Summary

karl Fischer method for the determination of acetic acid moisture is a highly technical work, which should be carried out in strict accordance with the experimental procedures. During the experiment, attention should be paid to the preparation and preservation of reagents, the pretreatment of samples, the calibration and maintenance of instruments, and the influence of environmental factors. Only through standardized operation and detailed analysis can the accuracy and reliability of the measurement results be ensured, and reliable data support can be provided for production and quality control.

Through the above analysis, we can see that the success of the Karl Fischer method for the determination of acetic acid moisture depends not only on the scientific nature of the experimental method, but also on the standardization of the experimental operation and the degree of detail treatment in place.