Derivatization of alkaloids for gas

A new method for the rapid separation of alkaloids, inter alia atropine, has been elaborated, using chromatography on paper that is impregnated with zirconium oxide.57 Cation-exchange h.p.l.c. analysis of tropane alkaloids has been developed,58 followed by post-column derivatization using the fluorimetric ion-pair technique.58,59 Gas chromatography of tropanes has been reviewed.60... 

HPLC analysis for pharmaceutical preparations of alkaloids started about 30 years ago. Gas chromatography (GC) is suitable for volatile compoxmds and requires laborious derivatization. Thus, GC is unsuitable to analyze the bisindole alkaloids due to their high boiling point. HPLC can provide better analytical precision and higher sample loading capacity. HPLC methods coupled to UV and MS detection have been applied for the determination of the active compounds in Catharanthus roseus. 

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... 

Floberg et al. applied glass capillary gas chromatography for the analysis of theophylline and caffeine in plasma. The alkaloids were analyzed as such, or after derivatization. 

Owing to the low volatility and thermal instability of many alkaloids, derivatization is performed to give them better gas chromatographic properties. Derivatization is, however, also done to give alkaloids better detection properties and for quantitative determinations. 

A number of various derivatization reactions have been used, as shown in Table 14.25. The derivatization has been carried out as off-column or on-column derivatization, mostly in order to give morphine and related alkaloids with phenolic or alcoholic hydroxyl groups better gas chromatographic properties. Especially for quantitative determination of morphine in opium or biological material such derivatization was necessary. Street et al. found, however, that the problem of adsorption of a phenolic alkaloid, such as morphine, because of "active sites" on the solid support could be solved by deactivation of the solid support by treatment of it (diatomaceous earth) with benzoyl chloride in pyridine before coating it with the stationary phase. 

Insufficient volatility and thermal stability are the biggest challenges in the application of gas chromatography for the analysis of steroids. The development of gas chromatography (GC) methods for steroids analysis should take in consideration thermal stability, the derivatization step to increase volatility, the stationary phase, and the detector. Several GC methods have been summarized for the analysis of various steroids including anabolic steroids, brassinosteroids, corticoids, estrogen, endocrine-disrupting chemicals, neurosteroids, sterols, steroid saponins, and steroid alkaloids. 

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