great variety of stationary phases is available to analyze an even larger array of compounds. Stationary phases in which organic moieties (alkyl chains, aryl, amine, cholesterolic, phospholipids, phenol groups, etc.) are grafted onto a silica surface are the most popular. Sometimes the stationary phases themselves must be characterized, such as for quality control purposes. Often, interpreting chromatographic data is difficult because even columns that are "identical"-produced by the same manufacturer-exhibit different chromatographic properties. Determining the structure and properties of new stationary phases is also extremely important so that the retention mechanism, which plays a significant role in selectivity, can be described accurately. Chromatographic separation occurs because of the differences in the affinities of solute molecules for the stationary phase-retention is a process of solute transfer from a mobile phase onto/into a stationary phase (1).Column quality depends on a number of factors, the most important of which are homogeneity of both particle packing in the column bed and arrangement of the chemically bonded phase on the adsorbent surface. These factors determine the reproducibility of chromatographic data, and the large number of these factors is why there are a lot of methods for characterizing columns. Obviously, no ideal single technique can characterize all the © 2 0 0 4 A M E R
Evaluation of HPLC columns: A study on surface homogeneity of chemically bonded stationary phasesThe aim of the current work is to study the heterogeneity of the adsorbent surface on the basis of physicochemical investigations and chromatographic tests. A series of packing materials with octadecyl chains chemically bonded to a silica matrix were prepared for this purpose. The surface and structural properties of bare silica and silica-based octadecyl phases were characterized by porosimetry, elemental analysis, 29 Si CP/MAS NMR, etc. The most advanced characterization methods based on adsorption microcalorimetry (heat of wetting) measurements were employed to obtain information about the heterogeneity and topography of unmodified and modified silica gel. For the chromatographic study, these phases were evaluated on the basis of the retention data under non-aqueous conditions. A test series of solutes with various chemical properties, such as pK a values, was used. It was found that heterogeneity of the packing surface results in low HPLC resolution. Use of a non-aqueous mobile phase (n-hexane) reduces analytical interference by eliminating hydrophobic interactions between alkyl ligands and the analyte.
The chemical character, geometry, and architecture of chemically formed surface layers determine interactions between stationary phase, analyte, and mobile phase, and therefore the retention mechanisms (partitioning, adsorption, ion exchange, steric exclusion) of separated analytes. These interactions also depend on the structure and chemical character of the solutes and the composition of the mobile phase. High-molecular-weight fullerenes (C60 and C70) and water-soluble selenium-containing peptides (833 and 2607 Da) were used for the evaluation of laboratory-prepared octadecyl stationary phases with high and low coverage density before and after end-capping. The aim of this work was to study differences in surface coverage density and homogeneity and conformational changes of chemically bonded moieties and the influence of these parameters on the separation of mixtures of selenopeptides and fullerenes with significantly different molecular masses. A topographical model of the chemically modified stationary surface is presented.
Analysis of the modified nucleosides is particularly important in the medical area because of a possibility of cancerogenic processes studies. The aim of this work was to study the selectivity tuning of modified nucleosides through the investigations of interactions analyte (modified nucleoside) <==> stationary phase <==> mobile phase. A series of homemade stationary phases with different surface properties has been utilized. All of them contain various interaction sites such as: cholesterol (SG-CHOL); n-acylamide (SG-CHOL, SG-AP); aminopropyl (SG-CHOL, SG-AP, SG-NH2, SG-MIX); cyanopropyl, phenyl, octyl (SG-MIX), octadecyl (SG-MIX, SG-C18) and silanols localized on the silica gel surface of all packings. The attempt to predict the main interactions responsible for the retention between nucleosides and stationary phase ligands was done on the basis of the elemental analysis, and proportional part of an individual ligand bonded to silica surface results. In order to study the influence of different packing types on the analyzed nucleosides retention, the relationship between pH of the mobile phase buffer and the selectivity of a stationary phase was investigated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.