Selective adsorption of plant products

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Abstract
The results from this study demonstrate that neutral resins can selectively concentrate specific indole alkaloids from dilute aqueous mixtures. Adsorption was observed to provide a one to two order of magnitude improvement in concentrating these alkaloids, as compared to an equivalent single‐staged extraction. Since the sorption correlates with the concentration of the neutral form of the dissolved alkaloid, the adsorption is dependent on both the pH of the medium and the pKa of the alkaloids. Also, adsorption is dependent on specific sorbent‐sorbate characteristics. In this study, by exploiting differences in the acid‐base properties and the sorption characteristics of specific indole alkaloids, separation factors of 20–30 were observed. Although this behavior is valuable for analytical separations, the present study considers the application to the primary recovery of alkaloids from plant cell processes. Throughout this study it was also observed that the polycarboxylic ester resin (XAD‐7) behaved quite differently from the styrene divinylbenzene resin (XAD‐4). Despite a lower capacity, the XAD‐7 resin was considerably more selective in adsorbing indole alkaloids than the XAD‐4 resin. These alkaloids could also be desorbed from the XAD‐7 resin by acidifying the liquid, while organic solvents were required to desorb these compounds from the XAD‐4 resin.