I. Preface

Citric acid, also known as citric acid, is an important organic acid and is commonly used as an acidity regulator and food additive. As a commonly used raw material for pharmaceuticals, there are clear indicators and requirements for its moisture content in the pharmacopoeia. That is, according to the moisture determination method in the pharmacopoeia, Karl. The Fischer volumetric method was used for determination. Dissolve the sample with methanol and use Karl. Titration was carried out with Fischer titrant.

This method adopts Carl. The Fischer volumetric method for determining the moisture content has good repeatability and can accurately measure the moisture content.

Ii. Instruments and Reagents

2.1 Instruments

JH-V5 Karl Fischer moisture titrator, analytical balance, etc

2.2 Reagents

Methanol, Karl Fischer titrant.

Iii. Experimental Methods

3.1 Sample Testing

Through the liquid discharge device of the moisture titrator, the residual liquid is removed. Then, 50mL of solvent methanol is added to the titration cup, with the solvent covering the electrode. After setting the parameters, the instrument starts the pre-titration. When the instrument is in standby mode, click on the system injection, open the rubber stopper of the feeding port, add the sample containing an appropriate amount of moisture to the titration cup, immediately cover the rubber stopper, and click Start measurement. Use Carl. Titrate the Fischer titrant to the endpoint, input the sample weight, and calculate the moisture content of the sample.

The parameters of the titrator are set as shown in Table 1:

Table 1 Titration Parameter Settings

Iv. Results and Discussion

4.1 Experimental Results

The experimental results are as shown in Table 2:

Table 2 Test Results

4.2. Conclusion

The moisture content of citric acid detected this time was 0.1204%. The data repeatability was good, the test was relatively rapid, and at the same time, it could reduce the influence of the external environment on the test results. Reduce the harm of experimental reagents to laboratory personnel.

References

[1] General Chapter 0832 Moisture Determination Method, Part IV, Chinese Pharmacopoeia 2020 Edition (Karl) The Pension Law [S].