L-Lysine-derived highly selective stationary phases for hydrophilic interaction chromatography: Effect of chain length on selectivity, efficiency, resolution, and asymmetry

Poly(carboxyethyl acrylate-co-ethylene glycol dimethacrylate) precursor monolith with bonded Tris ligands for use in hydrophilic interaction capillary electrochromatography

The facile preparation of a monolithic capillary column with surface bound polar ligands for use in hydrophilic interaction capillary electrochromatography is described. It involved the conversion of poly(carboxyethyl acrylate[CEA]-co-ethylene glycol dimethacrylate[EDMA]) precursor monolith (the so-called carboxy monolith) into a Tris bonded monolith by a post-polymerization functionalization process in the presence of a water soluble carbodiimide, namely N-(3-dimethylaminopropyl)-N´-ethylcarbodiimidehydrochloride. The carbodiimide assisted conversion, allowed the covalent attachment of the carboxyl group of the precursor monolith to the amino group of the Tris ligand via a stable amide linkage. This resulted in the formation of Tris poly(CEA-co-EDMA) monolith, which exhibited the typical retention behavior of hydrophilic interaction stationary phase when analyzing polar and slightly polar neutral or charged compounds. In fact, neutral polar species such as dimethylformamide, formamide and thiourea were retained in the order of increased polarity with acetonitrile rich mobile phase. Also, neutral p-nitrophenyl maltooligosaccharides (PNP-maltooligosaccharides) served as a polar homologous series for gauging the hydrophilicity of the Tris poly(CEA-co-EDMA) monolith, thus forming a versatile testing homologous series for other hydrophilic columns. Other polar anionic species (e.g., hydroxy benzoic acids and nucleotides) and weakly polar anionic compounds (e.g., dansyl amino acids and phenoxy acid herbicides) as well as polar weak bases namely nucleobases and nucleosides were used to probe the hydrophilic characters of the Tris poly(CEA-co-EDMA) monolith. The various polar and weakly polar compounds just mentioned revealed the wide potentiality of the hydrophilic interaction column under investigation.

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.