Effect of chromatographic conditions on the separation of selected alkaloids on phenyl stationary phase by an HPLC method

Some alkaloid standards and synthetic or natural alkaloid mixtures were chromatographed on phenyl-silica stationary phases using various aqueous eluents: aqueous methanol or acetonitrile mixture, buffered aqueous mobile phases at pH 3 to suppress silanols' ionisation, or at pH 8 to suppress alkaloids' ionisation. Strong silanophilic interactions that can occur with these analytes and the adsorbent surface can lead to poor peak shape and resolution. Mobile phases with anionic ion-pairs such as sodium dodecyl sulphate, octanesulfonic acid sodium salt, or HDEHP were used to improve efficiency, peak shape, and selectivity. The effect of silanol blockers - different amines on the retention, efficiency, and peak shape for RP systems, was analysed.