Probing the interaction of solvents with the stationary phase of C18 high-performance liquid chromatographic column material by variable-temperature dependent 129Xe nuclear magnetic resonance spectroscopy

• Published in: Journal of Chromatography A Vol. 1121; no. 1; pp. 23 - 31
• Main Authors: Chagolla, Danny, Mathias, Errol V., Ba, Yong
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 14.07.2006; Elsevier
• Subjects: 129Xe NMR; Analytical chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography, High Pressure Liquid - instrumentation; Exact sciences and technology; HPLC column material; Interaction of stationary phase and solvents; Magnetic Resonance Spectroscopy - methods; Other chromatographic methods; Silicon Dioxide - chemistry; Temperature; Interaction of stationary phase and solvents; 129Xe NMR; HPLC column material; Solvent effect; Reversed phase chromatography; HPLC chromatography; Xenon 129; NMR spectrometry; Mobile phase; Bonded stationary phase
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2006.03.117

VT 129Xe NMR was applied to probe the interactions of solvents having different polarity indices with the stationary phase of a RP-C18 HPLC column material. It was observed that the highly polar ethylene glycol molecules do not mix with the alkyl chains of the RP-C18 stationary phase and the solvent is unable to enter the pores and the spaces between the particles. Three phases in this sample are defined as stationary/xenon phase, xenon gas phase (in the pores and the spaces between the particles) and ethylene glycol/xenon phase. In contrast to ethylene glycol, the nonpolar solvent cyclohexane was observed to be well mixed with the RP-C18 stationary phase. The capillary rise effect allows the solvent to enter the pores and the spaces between the particles. Two phases in this sample are defined as stationary/cyclohexane/xenon phase and cyclohexane/xenon phases. The properties of ethyl acetate are between those of ethylene glycol and cyclohexane. The 129Xe NMR results show that the rational reversed phases should be conditioned from highly solvating to more polar solvents to remove the trapped air. The 129Xe NMR results also show that pure stationary phase exists only when a highly polar solvent is used in reversed-phase chromatography. For a solvent with lower polarity, a stationary/solvent phase actually forms. This, together with the mobile phase, determines the selective factor for separating mixtures.