Determination of Menthol Content in Mint by Gas Chromatogaphy

Chromatography Column: SK-WAX, 30m*0.32mm*0.25μm

Temperature-Programmed： Keep the column at an initial temperature of 70°C for 4 minutes, heat up to 120°C at a rate of 1.5°C per minute, then to 200°C at a rate of 3°C per minute, and finally to 230°C at a rate of 30°C per minute and keep for 2 minutes;

Carrier Gas: high purity nitrogen, constant Current Mode

Column Flow Rate: 2mL/min

Inlet Temperature: 200°C

Detector Temperature: 300°C

Hydrogen flow rate： 35mL/min

Air Flow Rate: 300mL/min

Injection Volume: 1μL

Injection Method: Split-flow injection with a 5:1 split ratio.

1.3 Reagents and Experiment Material

1.3.1 Reagents

Mint Sample

Menthol Standard

Ethanol, AR.

1.3.2 Equipment

Needle Filter

The third sieve

1.4 Sample Preparation

1.4.1 Preparation of Reference Solution

Take the appropriate amount of menthol control, precision weighing, add ethanol to make a solution containing 0.2mg per 1mL.

1.4.2 Preparation of Test Solution

Take 2g of product powder (through the third sieve), precision weighing, placed in a stoppered V-shaped bottle, and tightly stoppered after precision addition of 50mL of ethanol. Weighing, ultrasonic treatment (power 250W, frequency 33kHz) for 30 minutes, cooled, and then weighing. Make up the lost weight with ethanol, shake well, filter and take the subsequent filtrate.

2 Result and Communication

2.1 Chromatogram of Reference Solution

Take the reference solution and analyzed according to the test conditions of 1.2, and the results are shown below.

As shown in the figure and data, the peak shape is symmetrical, there is no other peaks, and the separation degree is higher than 1.5, which is good and met the requirements.

Take the reference solution, injected and detected 7 times sequential according to the test conditions in 1.2, the repeatability chromatogram as shown below. According to the test results, the retentionr time repeatability of the reference solution is 0.021% and the peak area repeatability is 0.47%, and the test repeatability is good.

2.2 Chromatogram of Test Solution

Take the test solution and analyzed according to the test conditions of 1.2, and the results as shown below. From the figure and the data, the peak shape is symmetrical, and there is no other peaks, and the separation degree is higher than 1.5, the separation is good and meets the requirements.

Take the reference solution, injected and detected 7 times sequential according to the test conditions in 1.2, the repeatability chromatogram as shown below. According to the test results, the retention time repeatability of the reference solution is 0.038% and the peak area repeatability is 0.49%, and the test repeatability is good.

3. Conclusion

In this paper, a method for the determination of menthol in mint is established by Wayeal gas chromatograph GC6000. The results showed that the menthol peaks in the chromatogram is symmetrical, the repeatability of the retention time of 7 injections is less than 0.5%, and the repeatability of the peak area is less than 0.5%, which showed a good test repeatability. The theoretical plate number is much higher than 10000, which meets the requirements of the Chinese Pharmacopoeia. This product is calculated according to the dry product, the content of menthol in the test sample is 0.50%, which meets the requirement of Pharmacopoeia of no less than 0.20%. This method can be a reference for the determination of menthol content in mint.