Mixed-mode HPLC columns allow for separation of compounds with drastically different properties. In this application, highly hydrophilic ascorbic acid is retained and separated from highly hydrophobic retinol and Vitamin E Acetate. Ascorbic acid is retained by anion-exchange mechanism and hydrophobic compounds are retained by reversed-phase mechanism. Compounds are monitored by UV detection. Mobile phase is compatible with LC/MS and method can be used to monitor basic and acidic compounds in bio-fluids (serum, blood, urine, saliva, etc.)