Quinine and quinidine are diastreoisomers. Quinine is an alkaloid with fever-reducing analgetic and anti-inflammatory properties. Both compounds have the same structure, and the only difference is optical position at two centers. These two diastereoisomers were separated on achiral mixed-mode cation-exclusion Primesep B column. No separation is observed on traditional achiral reversed-phase column. This examples shows that even diastereoisomers can be separated on mixed-mode HPLC columns.