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Open AccessArticle

Estimation of Solute-Stationary Phase and Solute-Mobile Phase Interactions in the Presence of Ionic Liquids

Departament de Química Analítica, Universitat de València, 46010 València, Spain
Separations 2019, 6(3), 40; https://doi.org/10.3390/separations6030040
Received: 5 June 2019 / Revised: 19 July 2019 / Accepted: 23 July 2019 / Published: 13 August 2019
(This article belongs to the Special Issue Recent Advances on Ionic Liquid Uses in Separation Techniques)
The presence of free silanols on alkyl-bonded reversed-phase stationary phases is responsible for broad and asymmetrical peaks when basic drugs are chromatographed with conventional octadecylsilane (C18) columns due to ionic interactions. In the last few years, ionic liquids (ILs) have attracted attention to reduce this undesirable silanol activity. ILs should be considered as dual modifiers (with a cationic and anionic character), which means that both cations and anions are able to adsorb on the stationary phase, creating a positively or negatively charged layer, depending on the relative adsorption. The accessibility of basic compounds to the silanols is prevented by both the IL cation and anion, improving the peak profiles. A comparative study of the performance of six imidazolium-based ILs, differing in their cation/anions, as modifiers of the chromatographic behavior of a group of ten β-adrenoceptor antagonists, is addressed. Mobile phases containing cationic amines (triethylamine and dimethyloctylamine) were used as a reference for the interpretation of the results. Using a mathematical model based on two chemical equilibria, the association constants between the solutes and modified stationary phase as well as those between solutes and the additive in the mobile phase were estimated. These values, together with the changes in retention and peak shape, were used to obtain conclusions about the retention mechanism, changes in the nature of the chromatographic system, and silanol suppression effect. View Full-Text
Keywords: ionic liquids; basic drugs; RPLC; peak shape; chemical equilibria ionic liquids; basic drugs; RPLC; peak shape; chemical equilibria
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Ruiz-Ángel, M.J. Estimation of Solute-Stationary Phase and Solute-Mobile Phase Interactions in the Presence of Ionic Liquids. Separations 2019, 6, 40.

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