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

• Published in: Journal of Chromatography A 2023-01, Vol.1689, p.463740, Article 463740
• Main Authors: Tereba-Mamani, C.J., Janczuk, M.A., Ruiz-Angel, M.J., García-Alvarez-Coque, M.C.
• Format: Article
• Language: English
• Subjects: Aqueous liquid chromatography; Ionic liquids; Sodium dodecyl sulphate; β-Adrenoceptor antagonists
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2022.463740

•Mixtures of ionic liquid and anionic surfactant explored for liquid chromatography.•Basic compounds separated with aqueous mobile phases without organic solvent.•Retention behavior is a combination of hydrophobic and ionic interactions.•Retention is modulated by varying the ratio of both additives.•Elution strength stronger compared to solutions with only surfactant or ionic liquid. In conventional reversed-phase liquid chromatography (RPLC) with hydro-organic solvents, basic cationic solutes yield retained, broad, asymmetric peaks, owing to their interaction with free anionic silanols in the stationary phase. RPLC mobile phases to which the anionic surfactant sodium dodecyl sulphate (SDS), or an ionic liquid (IL) are added, have been proposed as solutions, since these additives are able to block the silanol effect thus improving the chromatographic performance. With these additives, it is however necessary to increase the elution strength by adding an organic solvent, such as an alcohol or acetonitrile. A novel aqueous liquid chromatographic mode (in the absence of organic solvent) is here proposed, where the mobile phases contain only a mixture of aqueous solutions of SDS and an IL derived from 1-alkyl-3-methylimidazolium associated to chloride, both environmentally friendly. When these reagents are added, the anionic surfactant adsorbed on the stationary phase is able to attract the cationic solutes, whereas the adsorbed IL cation repels them. The combination of both effects (attraction and repulsion) allows the modulation of retention, by varying the IL/SDS ratio. Given the character of the additives, a type of green liquid chromatography is achieved. In this work, the chromatographic behavior of six basic compounds of pharmaceutical interest, the β-adrenoceptor antagonists acebutolol, atenolol, carteolol, metroprolol, oxprenolol and propranolol, is examined. In order to assess the chromatographic behavior of the mixed mobile phases containing SDS and IL, changes in retention, peak profile and resolution of mixtures of the analytes were explored at varying concentration of the additives.