Synthesis and evaluation of a pentafluorobenzamide stationary phase for HPLC separations in the reversed phase and hydrophilic interaction modes

Preparation of three structurally similar stationary phases with different ionizable terminal groups and evaluation of their retention performances under multiple modes in high performance liquid chromatography

Three structurally similar silane reagents with different terminal groups were prepared and bonded to silica to obtain three structurally similar stationary phases (Sil-Ph-COOH, Sil-Phe and Sil-Ph-NH2). The prepared stationary phases were characterized through elemental analysis (EA) and Fourier Transform Infrared Spectroscopy (FT-IR). These three stationary phases provided acceptable retention repeatability (relative standard deviations between 0.08% and 0.13%) and high column efficiency (7.3 × 104 plates/m for uridine on Sil-Phe). The retention behavior of the three columns was investigated under different chromatographic conditions including different mobile phase ratio, salt concentration, pH etc. The retention mechanisms were explored by linear solvation energy relationships and Van't Hoff plots. Applications in separation under reversed phase liquid chromatography (RPLC), hydrophilic interaction liquid chromatography (HILIC) and ion exchange chromatography (IEC) mode were investigated. The results showed that the retention capacity of the stationary phases with different terminal groups to the analytes is very different, especially for carboxylic acids, because the surface charges of amino groups and carboxyl groups under weakly acidic conditions produce different electrostatic effects with dissociated carboxylic acids. Finally, the Sil-Phe column was employed to detect ibuprofen extracted from pharmaceutical ibuprofen capsules and vitamins extracted from vitamin tablets.

A Compendium of the Principal Stationary Phases Used in Hydrophilic Interaction Chromatography: Where Have We Arrived?

Hydrophilic interaction liquid chromatography (HILIC) today is a well-known and largely applied technique to analyse polar compounds such as pharmaceuticals, metabolites, proteins, peptides, amino acids, oligonucleotides, and carbohydrates. Due to the large number of stationary phases employed for HILIC applications, this review aims to help the reader in choosing a proper stationary phase, which often represents the critical point for the success of a separation. A great offer is present for achiral applications in contrast to the chiral phases developed for HILIC enantioseparations. In the last case, up-to-date solutions are presented.

A Survey of Polar Stationary Phases for Hydrophilic Interaction Chromatography and Recent Progress in Understanding Retention and Selectivity

Various polar stationary phases have become available for hydrophilic interaction chromatography (HILIC) and help drive continuous applications in biomedical, environmental and pharmaceutical areas in the past decade. Although the stationary phases for HILIC have been reviewed previously, it is an appropriate time to take another look at the progresses during the past five years. The current review provides an overview of the polar stationary phases commercially available for HILIC applications in an effort to assist scientists in selecting suitable columns. New types of stationary phase that were published in literature in the past five years are summarized and discussed. The trend in stationary phase research and development is also highlighted. Of particular interest is the experimental evidence for direct interactions of polar analytes with the ligands of the stationary phases under HILIC conditions. In addition, two different approaches have been developed to delineate the relative significance of the partitioning and adsorption mechanisms in HILIC, representing an important advancement in our understanding of the retention mechanisms in HILIC.

Synthesis and chromatographic evaluation of a new stationary phase based on mild thiol-Michael addition reaction

Click chemistry has attracted increasing attention for the synthesis of novel stationary phases. Considering the advantage of click chemistry, a strategy based on thiol-Michael addition was developed for the preparation of a new stationary phase herein, and a phenyl vinyl sulfone stationary phase (M-PVS) was prepared. The resulting M-PVS bonded silica was characterized by elemental analysis, solid-state ¹³C cross-polarization/magic-angle spinning NMR and infrared spectroscopy, confirming the successful immobilization of phenyl vinyl sulfone on the silica support. The retention properties of M-PVS were investigated and exhibited unambiguous reversed phase retention characteristics. Moreover, shape selectivity and silanol activity were studied to reveal the diverse interactions of M-PVS, including hydrophobic, π-π, hydrogen bonding, and ion-exchange interactions. In addition, de-wetting tolerance and hydrophilic properties were evaluated and a pronounced "U" retention curves were obtained, indicating enhanced retention for polar analytes and transitions of different interaction modes. Selectivity differences between M-PVS column, phenyl column and conventional C₁₈ column were examined using series natural standards. The diverse interactions of M-PVS demonstrated its improved selectivity for the compounds with similar hydrophobic skeleton but different polar substituents.

Tetra-proline-modified calix[4]arene-bonded silica stationary phase for simultaneous reversed-phase/hydrophilic interaction mixed-mode chromatography

A new water-soluble tetra-proline-modified calix[4]arene-bonded silica stationary phase was prepared straightforwardly by an indirect method and characterized by elemental analysis, energy dispersive Spectrometry, solid-state ¹³ C NMR spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. Due to the simultaneous introduction of polar tetra-proline and nonpolar calix[4]arene, the developed column possessing a double retention mode of reverse-phase liquid chromatography and hydrophilic interaction liquid chromatography. A series of hydrophobic and hydrophilic test samples, including nucleosides and nucleotides, amines, monosubstituted benzenes, chiral compounds, and phenols, were used to evaluate the developed stationary phase. A rapid separation capability, high separation efficiency, and selectivity were achieved based on the multiple interactions between solutes and tetra-proline-modified calix[4]arene-bonded silica stationary phase. Moreover, the developed stationary phase was further used to detect and separate hexamethylenetetramine in rice flour. All the results indicated the potential merits of the developed stationary phase for simultaneous separation of complex hydrophobic and hydrophilic samples with high selectivity.