Hydrophilic Liquid Chromatography versus Reversed-Phase Liquid Chromatography in the Absence and the Presence of 1-Hexyl-3-methylimidazolium Chloride for the Analysis of Basic Compounds

In reversed-phase liquid chromatography (RPLC), positively charged basic compounds often produce broad, asymmetric peaks due to ionic interactions with free silanols on conventional silica-based columns. Various methods have been proposed to mask silanophilic activity, improving peak shape. This study evaluated hydrophilic interaction liquid chromatography (HILIC) as an alternative to adding an ionic liquid (IL) to the aqueous-organic mobile phase used with RPLC columns for analysing eight β-adrenoceptor antagonists. ILs alter the behaviour of RPLC stationary phases by adsorbing onto their surfaces, while HILIC forms an adsorbed water layer on the stationary phase. The complex retention mechanisms involve cationic basic compounds associating with additive ions, hydrophilic partitioning in HILIC, and other interactions. The chromatographic behaviour was assessed based on retention, elution strength, selectivity, peak shape, and resolution, using acetonitrile-water mobile phases at pH 3. Both RPLC with ILs and HILIC effectively addressed the issue of poor peak shape for basic compounds.