Reversed-phase high-performance liquid chromatographic separation of potato glycoalkaloids and hydrolysis products on acidic columns

As part of a program of potato improvement, improved procedures were developed for reversed-phase high-performance liquid chromatographic (HPLC) separation of the alkaloids present in commercial potatoes: the two major glycoalkaloids, alpha-chaconine and alpha-solanine; hydrolysis products or metabolites derived from these two compounds, the so-called beta- and gamma-chaconines and solanines; and their aglycon, solanidine. For comparison, we also included the glycoside solasonine, present in wild potatoes, and its aglycon solasodine. Column "acidity", caused by active silanol sites on the packing's surface, was found to strongly influence chromatographic separation of Solanum alkaloids. Ten commercially available HPLC columns with reversed-phase packings in a total of 13 configurations were evaluated for relative acidity, with the aid of two standards: diphenhydramine and 5-(p-methylphenyl)-5-phenylhydantoin. Resolution of the glycoalkaloids improved with increasing acidity. The peaks associated with the glycoalkaloids lacked the tailing and excessive retention usually observed with basic compounds on acidic columns. The aglycons, however, required a nonacidic column for optimum chromatography. These studies facilitated choosing conditions to optimize the separation and quantitative estimation of Solanum alkaloids, both in pure form and in potato extracts, and proved the usefulness of acidic columns in certain applications. The possible value of these findings to food safety and plant physiology is discussed