Investigation of the temperature dependence of water adsorption on silica-based stationary phases in hydrophilic interaction liquid chromatography

Silica Hydride: A Separation Material Every Analyst Should Know About

This review describes the development, special features and applications of silica hydride-based stationary phases for HPLC. The unique surface of this material is in contrast to ordinary, standard silica, which is the material most frequently used in modern HPLC stationary phases. The standard silica surface contains mainly silanol (Si-OH) groups, while the silica hydride surface is instead composed of silicon-hydrogen groups, which is much more stable, less reactive and delivers different chromatographic and chemical characteristics. Other aspects of this material are described for each of the different bonded moieties available commercially. Some applications for each of these column types are also presented as well as a generic model for method development on silica hydride-based stationary phases.

Adsorption mechanism of triterpenoid saponins in reversed-phase liquid chromatography and hydrophilic interaction liquid chromatography: Mogroside V as test substance

In this paper, adsorption mechanism of triterpenoid saponins in reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) was proposed based on the study of the retention behavior of mogroside V as test substance. The change of peak shape of mogroside V and its influencing factors was first investigated. As the increase of sample loading, a tailing peak of mogroside V was observed in MeOHH₂O of both two modes. It was the fronting peak in ACNH₂O of HILIC while there was a transition from fronting peak to tailing peak in ACNH₂O of RPLC that was largely affected by column temperature and ACN concentration. The adsorption isotherm of mogroside V in ACNH₂O of RPLC was fitted by Moreau model, where a monolayer adsorption with large inter-molecular interaction was formed on the C18 surface. While in ACNH₂O of HILIC, the adsorption of mogroside V was in accordance with BET model, showing multilayer adsorption behavior. In MeOHH₂O of both HILIC and RPLC, there was always monolayer adsorption, which was fitted by Langmuir model. At last, by choosing the suitable chromatographic mode, controlling the key factors such as the solvent concentration and column temperature, and predicting the broadening trend of peak, three methods were screened out, namely, C18 column with 22% ACN (30 °C), Click XIon column with 90% MeOH or 70% ACN, to get mogroside V of purity greater than 98% from Siraitia grosvenorii extract. Among them, the RPLC method of 22% ACN that showed the highest loading sample per hour (1.92%) and the lowest solvent consumption emerged as the best approach.

Sources of Nonlinear van't Hoff Temperature Dependence in High-Performance Liquid Chromatography

In HPLC, the nonlinear behavior of the retention factor k' with temperature (dependence of ln k' on 1/T) can be attributed to the multiple interactions of a unique analyte in the separation process and/or to the existence in solution of multiple forms of the analyte (also leading to different free enthalpies of interaction). In this study, several examples of nonlinear retention-temperature dependence are evaluated for both reversed-phase (RP) and hydrophilic interaction chromatography (HILIC) separations. The potential explanation for nonlinear retention-temperature behavior is evaluated for each example, some caused by multiple interactions in the separation system of a unique analyte and others by multiple forms of the analyte. In cases where the analyte does not have more forms and the separation is based predominantly on one type of interaction (e.g., hydrophobic interaction in RP-HPLC), the dependence is linear, as expected. By studying the changes in the chemical structure of a compound as a function of pH it is possible to decide, in many cases, if a unique form or multiple forms of a compound are present in the solution. The use of this information allows us to determine when the lack of linearity (when present) is caused by multiple interactions in the separation system (for one form of the compound) and when more forms are causing the lack of linearity. The approximation with a quadratic form for the nonlinear dependence has been verified in most cases to be good, and only minor improvements were obtained when using higher polynomial dependencies.