Dimethyl sulfoxide is important polar aprotic solvent, which is frequently used in pharmaceutical drug manufacturing, desolution, etc. DMSO is used as one of the solvents on protein chemistry due to universal ability to dissolve small molecules like amino acids. Amino acids and DMSO are very polar and have no retention on reversed-phase columns. In this HPLC application DMSO and glycine are separated on Primesep 100 mixed-mode column. DMSO is retained by weak reversed-phase mechanism and very low organic concentration is required in order to achieve any retention. Glycine, like any other underivatized amino acid, is retained by weak reversed-phase and moderate cation-exchange mechanism. Method uses acetonitrile/water/TFA gradient and UV detection.