Paper electrophoresis of pyrrolizidine alkaloids

Abstract

The electrophoretic mobilities of 27 pyrrolizidine alkaloids and related compounds are recorded for seven electrolytes. In non- complexing electrolytes the compounds migrate as cations, and electrophoresis at controlled pH affords useful separations of mixtures, depending on differences in molecular weight and base strength of the alkaloids.     In sodium borate and sodium arsenite, compounds containing vicinal glycol groups also form anionic complexes to an extent determined by their stereochemistry, and the cationic migration is reduced or changed into anionic migration. Electrophoresis in complex-forming electrolytes permits easy separation of some alkaloids which are chromatographically indistinguishable, such as esters of trachelanthic and viridifloric acids. Electrophoresis in borate is analytically useful for the separation and determination of alkaloids of Heliotropium europaeum L.     Electrophoresis gave no evidence for interaction between the alkaloids and copper, lead, or zinc ions in neutral or slightly acidic solution.     Marked reduction of the cationic mobilities of the alkaloids occurs in phosphate buffer at or near neutrality and is probably caused by formation of ion-pairs from alkaloid cations and phosphate ions. The mobilities of diesters of retronecine are most strongly depressed, suggesting that a common structural feature in these alkaloids is especially favourable for association with phosphate ions.