Determination of Menthol in Gel Analgesic Patch by Gas Chromatography with Solvent Extraction

In view of the large consumption of organic reagent and inconsistency between the determined value and the label value in the existing methods, the method as mentioned by the article was proposed. About 0.1 g of the sample was taken and placed into a headspace bottle after removing the anti-stick layer. After 5 mL of DMF was added, the mixture was shaken for 10 s, and heated at 80 ℃ for 1 h. An aliquot (2 mL) of the solution obtained was taken and centrifuged for 1 min. The supernatant of 100 μL was taken, diluted to 1 mL with ethyl acetate, and analyzed by gas chromatograph. Menthol was separated by VF-17ms capillary chromatographic column, and detected by flame ionization detector (FID). As found by the results, mass concentrations of menthol showed a linear relationship with peak areas in the range of 10-500 mg·L^-1, with detection limit (3S/N) of 0.02 mg·kg^-1. Tests for precision and spiked recovery were made on actual samples, and RSDs (n=6) of the determined values was 1.4%, giving recoveries in the range of 97.1%-103%. Compared with the method for detection of menthol powder in the pharmacopoeia of the People's Republic of China (2020 edition), there was a significant difference between the 2 methods, and some values determined by the pharmacopoeia method were lower than the label values. The proposed method was used for the analysis of 6 actual samples, and satisfactory results were obtained.