Improving the Understanding of the Properties and Retention Behavior of Chemically Bonded Stationary Phases Employing Suspended-state HR/MAS NMR Spectroscopy

Molecular recognition processes are predicted to become the basis of all advanced separation techniques. In solution and recently also in suspension ligand-receptor interactions can be studied using methods of high-resolution (HR) suspended-state NMR spectroscopy, for example by employing the saturation transfer difference (STD) NMR technique. In this approach molecular recognition processes of (R) and (S)-flurbiprofen on different derivatized polysaccharide-based silica chiral stationary phases (CSP) typically used in high performance liquid chromatography (HPLC) have been investigated. In addition to chromatographic investigations suspended-state high-resolution/ magic angle spinning (HR/MAS) NMR measurement were performed. A separation of racemic flurbiprofen was obtained on two out of three CSP column materials under identical chromatographic conditions. Hence, we expected significant different binding affinities resulting in spatial interactions stabilizing one transient diastereomeric complex relative to the other. Due to these differences we used for screening purposes T1 relaxation time measurements and the saturation transfer difference (STD) NMR methodology to study the interaction strength between (R) and (S) enantiomers and the three CSP materials used. Thus, saturation transfer difference (STD) NMR experiments can provide valuable information for the design and implementation of novel, task-specific or tailored stationary phases.