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Droplet counter-current chromatography of alkaloids. The influence of ph-gradients and ion-pair formation on the retention of alkaloids.

The separation of the alkaloids strychnine, brucine, quinine, dihydroquinine, and berberine by using pH-gradients in Droplet Counter-Current Chromatography was studied. Gradients from pH 8-2.5 resulted in separation of the alkaloids mentioned. It was further concluded that the anions play an important role in the distribution of the alkaloids between the organic and aqueous phase. Based on these conclusions a solvent system is proposed consisting of a pH = 4 Mcllvaine buffer containing 1 M sodium perchlorate - methanol - chloroform (3:5:5), using the aqueous phase as mobile phase (ascending mode) for the separation of the alkaloids. By using a gradient with a decreasing concentration of the counterion, the retention time of the alkaloids can be reduced.