High performance liquid chromatography of selected alkaloids in ion-exchange systems

A HPLC procedure on strong cation exchange column (SCX) has been developed for the analysis of selected alkaloids from different chemical groups. The retention, separation selectivity, symmetry of peaks and system efficiency were examined in different eluent systems containing different types or concentrations of buffers at various pH and the addition of organic modifiers: methanol (MeOH), acetonitrile (CH3CN), tetrahydrofuran (THF) or dioxane (Dx). The retention factors as the function of the concentration of buffers, the mobile phase pH and the percentage of modifier in the eluents were investigated. More symmetrical peaks and the highest theoretical plate number were obtained in eluents containing acetonitrile or tetrahydrofuran. In most cases, the increase of buffer concentration caused the decrease of alkaloids' retention, the improvement of peaks' symmetry and the increase of theoretical plate number. The improved peak symmetry and the efficiency of system for most investigated alkaloids were observed in the systems containing buffers at strongly acidic pH. The obtained results also reveal a large influence of salt cation used for buffer preparation. The results obtained on SCX column were compared with those obtained on a C18 column. The most efficient and selective systems were used for the separation of alkaloid standard mixture.