Aqueous liquid chromatography with mobile phases of sodium dodecyl sulphate and ionic liquid

In conventional reversed-phase liquid chromatography (RPLC) with hydro-organic solvents, basic cationic solutes create broad, asymmetric peaks due to interactions with free anionic silanols in the stationary phase. To mitigate this, mobile phases using the anionic surfactant sodium dodecyl sulphate (SDS) or ionic liquids (ILs) have been proposed, as these additives block the silanol effect and enhance performance. However, improving elution strength typically requires organic solvents like alcohol or acetonitrile. This study presents a novel aqueous chromatographic mode that eliminates organic solvents, utilising only a mixture of aqueous SDS and an environmentally friendly IL derived from 1-alkyl-3-methylimidazolium with chloride. In this setup, the SDS adsorbed on the stationary phase attracts cationic solutes, while the IL cation repels them, allowing for retention modulation by varying the IL/SDS ratio, thus achieving green liquid chromatography. The research investigates the chromatographic behaviour of six pharmaceutical β-adrenoceptor antagonists: acebutolol, atenolol, carteolol, metoprolol, oxprenolol, and propranolol. It explores changes in retention, peak profiles, and resolution of analyte mixtures at varying SDS and IL concentrations.