Temperature Responsive × Fast Chiral Comprehensive Liquid Chromatography: a New 2D-LC Platform for Resolving Mixtures of Chiral Isomers

Chiral resolution of solutes occurring in mixtures of unrelated species is of relevance in life sciences and in pharmaceutical analysis. While this is conceptually achievable by comprehensive two-dimensional liquid chromatography (LC × LC), few approaches exist whereby the second dimension comprises the chiral separation. The latter is preferable in combination with a conventional reversed phase type of separation in the first dimension as it offers an extension of a conventional achiral analysis. The implementation of such rapid chiral analyses in the second dimension was, thus far, limited by the challenging transfer of the first dimension mobile phase to the second dimension while still achieving chiral separation. In this study, the combination of temperature-responsive and reversed-phase chiral liquid chromatography is assessed in terms of enantioselective separation of a broad range of pharmaceutical compounds. Applying temperature-responsive liquid chromatography (TRLC) in the first dimension allows for analyses to be performed under purely aqueous conditions, which then allows for complete and more generic refocusing of (organic) solutes prior to the second dimension. This offers an enhanced ability to employ fast and broad compositional gradients over the chiral dimension, which broadens the applicability of the technique. In the proposed platform, seven chiral columns (superficially porous and fully porous columns (comprising both polysaccharide and macrocyclic antibiotic phases)) and four mobile phase gradients were screened on a pharmaceutical test mixture. The platform was shown to be able to offer the necessary resolving power for the molecules at hand and offers a new approach for chiral screening of mixtures of unrelated compounds.