Identification, and Determination Procedures

The methods employed for isolation of the alkaloids depend on the nature of the compounds, and specific conditions have frequently been devised for the selective isolation of particular types of compounds. Usually, fresh or dried plant material is extracted with dilute acid solution or with alcohol, and the extract obtained is further fractionated by extraction into organic solvents with variation of pH. Extraction columns (288), membrane processes (425), and ion-exchange materials (288-290) may be particularly useful for subfractionation or isolation procedures. For further identification and isolation of separate compounds, preparative thin-layer chromatography, (288, 291, 292, 426), liquid chromatography (293, 294), or gas chromatography may be used (202, 296, 297). Because some of the products reviewed in this chapter occur naturally in very small amounts, they have not been isolated in crystalline form. Gas chromatography-mass spectrometry (87, 213, 299), mass fragmentography (192), and mass spectrometry-mass spectrometry (301, 359) have proved to be particularly useful techniques for identification of trace alkaloids in complex mixtures. 

The oriental crude drug Mao (Epedrae Herba) is contained in various oriental pharmaceutical preparations (255). Since the content of ephedrine alkaloids in this drug may vary with the Ephedra species used for its preparation and with, e.g., harvest conditions, it has been important to develop quantitative analytical methods in order to evaluate the quality. 

In recent years several sensitive and specific methods for the simultaneous determination of ephedrine alkaloids in plant material have been published. These include thin-layer chromatography (292,426), gas chromatography (251), straight-phase and reversed-phase high-performance liquid chromatography (253, 255, 302, 355, 427), isotachophoresis (303, 356), and 13C-NMR (304). Resolution of enantiomeric alkaloids by HPLC has been achieved on chiral stationary phases (417, 418) or after derivatization with a chiral agent on an achiral stationary phase (419). Chromatographic separation and analytical detection of 

---