Optimization of the Mobile Phase for HPLC Separation of S-Alk(en)yl-L-Cysteine Derivatives and Their Corresponding Sulfoxide Isomers

Using the "PRISMA" optimization model, a total of 15 S-alk(en)yl-L-cysteine derivatives, including five thioethers and their corresponding sulfoxide isomers, could be separated following pre-column derivatization with o-phthaldialidehyde/tert.-butylthiol. Optimal isocratic separation of the sulfoxides was achieved with a limited number of experiments using a quaternary solvent system consisting of tetrahydrofuran, 1,4-dioxane, acetonitrile, and aqueous phosphate buffer of pH 7.15. Using a selective multisolvent gradient elution (SMGE) techniqe, which involves a simultaneous change in selectivity and solvent strength of the mobile phase, the full range of the examined sulfur amino acids (most of them are found in various Allium species) could be resolved in a single chromatographic run. Development and realization of the chromatographic optimization is shown and discussed. A simple computer program (written in Microsoft Basic) for the calculation of the actual mobile phase composition is added.