Analysis of alkaloids in Lotus (Nelumbo nucifera Gaertn.) leaves by non-aqueous capillary electrophoresis using ultraviolet and mass spectrometric detection

Lotus leaves are a popular remedy in Asia to treat obesity, insomnia and mental impairment; alkaloids are considered most relevant for bioactivity. In this study the first CE method for the determination of all major alkaloids ((−)-nuciferine, (−)-nornuciferine, (−)-caaverine, (−)-armepavine, (+)-norarmepavine, (+)-isoliensinine and (+)-pronuciferine) in Nelumbo nucifera leaves was developed. The optimum buffer showed to be a solution of 100 mM ammonium acetate in a mixture of methanol, acetonitrile and water, also containing 0.6% acid acetic. Applied voltage, temperature and detection wavelength were 25 kV, 30 °C and 225 nm; the required analysis time was 15 min. By CE–MS all standard compounds could be assigned in positive ESI mode, and two minor alkaloids were tentatively identified (n-nornuciferine and roemerine). A mixture of water, methanol and acetic acid served as sheath liquid in these experiments. The NACE assay was fully validated and utilized to analyze Lotus leaf samples collected in different parts of Vietnam. Respective results revealed significant qualitative and quantitative differences depending on growing area and season. Yet, in all samples (−)-nuciferine (0.34–0.63%), (−)-armepavine (0.13–0.20%), and (+)-isoliensinine (0.06–0.19%) were the most dominant alkaloids. The total alkaloid content varied from 0.72 to 1.41%.