Nonaqueous capillary electrophoresis‐electrospray ionization‐ion trap‐mass spectrometry analysis of pyrrolo‐ and pyrido[1,2‐a]azepine alkaloids in Stemona

Stemona alkaloids represent an outstanding class of natural compounds due to their pharmacological profile and their complex and unusual molecular structures. The aim of this study was the development of the first CE method for the separation, identification and quantification of these pyrrolo- and pyrido[1,2-a]azepine derivatives in three Stemona species. The best results were obtained with a NACE-ESI-IT-MS method, utilizing an electrolyte of 50 mM ammonium acetate, 1 M acetic acid and 10% methanol in ACN and a separation voltage of 30 kV. Samples were injected voltage-assisted with 20 kV for 1 s. Isopropanol:water (1:1) was used as ESI sheath liquid at a flow rate of 3 microL/min. The assay was applied for the qualitative profiling of Stemona alkaloids in S. curtisii, S. collinsae and S. tuberosa. For unambiguous peak assignment of more than forty unidentified alkaloids MS/MS experiments were performed and fragmentation patterns studied. Subsequently the method was validated for the quantitative determination of four selected derivatives (RSD inter- and intraday <6%, LODs <7.5 microg/mL, LOQs <25.0 microg/mL, for all analytes, recovery rates >98.9%) in several Stemona sp. extracts.