1. Preface

Formaldehyde is usually a colorless gas with a pungent smell. It is highly soluble in water and ether, and the maximum concentration of its aqueous solution can reach 55%. The formaldehyde content of the conventional reagents in the laboratory is approximately 37% to 40%. Usually, 8% to 14% methanol is added to prevent polymerization. Therefore, during the production process of formal reagent, to ensure the stability of its solution, it is necessary to control the proportion of the three well to prevent polymerization. Since water accounts for the largest proportion, detecting the moisture content is one of the effective methods to control its production.

The volumetric method for determining the moisture content of formaldehyde can quickly and accurately detect the moisture content of formaldehyde, providing an accurate and efficient basis for the determination of formaldehyde moisture.

2 Instruments and equipment

2.1 Instruments

JH-V3 Karl Fischer moisture titrator (volumetric method), double platinum electrodes, 5mL titration unit.

2.2 Reagents

Karl Fischer titrant two-component (for aldehydes and ketones).

3 Experimental Methods

3.1 Experimental Procedures

Through the liquid discharge device of the moisture titrator, the residual liquid is removed. Then, 50mL of solvent (specifically for aldehydes and ketones) 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, and add the sample to the titration cup with a syringe (the mass of the added sample is calculated by the difference method). Immediately cover the rubber stopper, click "Start Measurement", and use Karl. Titrate the Fischer titrant (specifically for aldehydes and ketones) to the endpoint, input the weighing amount of the sample, and calculate the moisture content of the sample.

Table 1  Parameter Settings

4 Results and Discussion

4.1 Experimental Results

Calculation formula:

In the formula:

X - represents the moisture content of the sample (%);

V1 - The volume (mL) of titration liquid consumed when titrating the sample;

m - The weighing amount of the sample (g);

T - represents the concentration of the titrant (mg/mL).

4.2 Conclusion and Discussion

The moisture content of formaldehyde was determined by the JH-V3 Karl Fischer moisture titrator (volumetric method). The data repeatability was good, and the measured moisture content was about 47%. The repeatability of the measured data was good, and the RSD value was about 0.6%, which could accurately detect the formaldehyde content.

References

[1] GB/T6283 Determination of Moisture in Chemical Products, Karl. The Fischer method (general method).[S]