Preparation and quality evaluation of a volatile oil microemulsion from Flos magnoliae and Centipeda minima

In order to improve the water solubility of the volatile oils extracted from Flos magnoliae (FM) and Centipeda minima (CM), they were prepared as a microemulsion (ME), which were then used in the development of an FM and CM volatile oil ME for the treatment of allergic rhinitis (AR). ME was prepared by phase inversion emulsification, and the prescription factors such as emulsifier, co-emulsifier, oil phase, Km, which represents the ratio of the mass of emulsifier to that of the co-emulsifier, and preparation factors such as temperature affecting the formation of the ME were selected according to the formation area of ME in a pseudo-ternary phase diagram. The quality of the ME was evaluated based on its appearance, particle size, Zeta potential and stability. The content of eucalyptol in ME was determined by gas chromatography-mass spectrometry (GC-MS). The cumulative permeability of the ME within 24 h was measured with a transdermal diffusion tester. The results revealed that the best formula for preparation of the ME was as follows: Castor oil polyoxyethylene ether (EL-40) was the emulsifier; the co-emulsifier was anhydrous ethanol; the Km was 2:1; the mixed phase of volatile oil and isopropyl myristate with mass ratio of 1:1 was used as oil phase; and the preparation temperature was 25°C. The content of eucalyptol in the ME was 2.57 mg/g, and the cumulative permeability of the ME in 24 h was significantly increased compared with that of the reference oil solution. The appearance of the ME was uniform, and the solution was transparent. In conclusion, compared with traditional preparations, FM and CM volatile oil ME is a novel, improved and more effective preparation for the treatment of AR.