In reversed-phase liquid chromatography, cationic basic compounds often produce broad, asymmetrical peaks due to ionic interactions with anionic silanol groups on silica-based stationary phases (typically C18-derivatised). A common method to improve peak shape is adding a cationic reagent (additive) to the mobile phase, which associates with the stationary phase, blocking analyte access to silanol groups. Cationic additives interact with anionic silanols and may also align with the stationary phase's alkyl chains, preventing silanol access. This results in a positively charged stationary phase, repelling protonated basic compounds, which elute quickly unless sufficiently non-polar. This study compares the performance of various amines and ionic liquids (1-butyl-3-methylimidazolium chloride and 1-hexyl-3-methylimidazolium chloride) as additives. Results showed that additive size and adsorption ability primarily determine their effectiveness in blocking silanol activity.
