查看更多>>摘要：Pavel Jandera was a world‐leading analytical chemist who devoted his entire professional life to research in the field of high‐performance liquid chromatography. During his scientific career, he worked at the Department of Analytical Chemistry at the University of Pardubice, Czech Republic. His greatest contribution to the field of liquid chromatography was the introduction of a comprehensive theory of liquid chromatography with programmed elution conditions. He was also involved in the research of gradient elution techniques in preparative chromatography, modeling of retention and selectivity in various phase systems, preparation of organic monolithic microcolumns, and, last but not least, in the development of theory and practical applications of two‐dimensional liquid chromatography, mainly in the comprehensive form. In this review article, we have tried to capture the highlights of his scientific career and provide the readers with a detailed overview of Pavel Jandera's contribution to the evolution of separation sciences.
查看更多>>摘要：The current performance of commercially packed liquid chromatography columns is limited by the random structure of the packed bed and by the wall‐to‐center heterogeneity of its structure. The minimum reduced plate heights observed are not smaller than 1.4, whereas they could theoretically be as low as 0.1 for dense and perfectly ordered packings of spheres. To bridge this gap, a wide inner diameter column with an ordered macroporous structure is printed in three dimensions by stereolithography of poly(ethylene glycol diacrylate) resin. Feature sizes below 100?μm are achieved by combining conventional polymer stereolithography with photolithography using photomasks. A layer‐by‐layer polymerization is performed by alternating two distinct photomasks having horizontally and vertically oriented patterns. Despite the inevitable printing imperfections, minimum reduced plate heights around unity are measured for nonretained analytes. The next challenges for the successful printing of highly efficient and large volume liquid chromatography columns are threefold: reducing the feature size down to below 10?μm, keeping minimum the unevenness of the flow channel dimensions, and tackling additive manufacturing of silica aerogels at such small feature sizes for higher mechanical stability and broader range of retention/selectivity than those delivered by polymer materials.
查看更多>>摘要：In liquid chromatography, it is often very useful to have an accurate model of the retention factor, k, over a wide range of isocratic elution conditions. In principle, the parameters of a retention model can be obtained by fitting either isocratic or gradient retention factor data. However, in spite of many of our own attempts to accurately predict isocratic k values using retention models trained with gradient retention data, this has not worked in our hands. In the present study, we have used synthetic isocratic and gradient retention data for small molecules under reversed‐phase liquid chromatography conditions. This allows us to discover challenges associated with predicting isocratic k values without the confounding influences of experimental issues that are difficult to model or eliminate. The results indicate that it is not currently possible to consistently predict isocratic retention factors for small molecules with accuracies better than 10%, even when using synthetic gradient retention data. Two distinct challenges in fitting gradient retention data were identified: 1) a lack of ‘uniqueness’ in the parameters and 2) an inability to find the global optimum fit in a complex fitting landscape. Working with experimental data where measurement noise is unavoidable will only make the accuracy worse.
Josef PlanetaDana MoravcováPavel KarásekMichal Roth...
8页
查看更多>>摘要：Highly crosslinked monolithic capillary columns with inner diameters in the range of 50–530?μm were prepared by radical polymerization of pentaerythritol tetraacrylate, polyhedral oligomeric silsesquioxane‐methacrylate, and n‐octadecyl methacrylate in the presence of methanol, dodecyl alcohol, and polyethylene glycol lauryl ether. Columns were evaluated by inverse size‐exclusion chromatography employing a set of polystyrene standards of narrow molecular‐size distribution and by scanning electron microscopy. Chromatographic performance under reversed‐phase conditions was also evaluated. The combination of two effective crosslinkers as pentaerythritol tetraacrylate and polyhedral oligomeric silsesquioxane‐methacrylate in the polymerization mixture allows for the preparation of robust and efficient monolithic capillary columns within a fairly wide range of internal diameters.
Martin GilarKenneth D. BertheletteThomas H. Walter
12页
查看更多>>摘要：We compared the separation selectivities of 19 different hydrophilic interaction chromatography columns. The stationary phases included underivatized silica and hybrid particles, cyano‐bonded silica, materials with neutral ligands such as amide, diol, pentahydroxy, and urea, zwitterionic sorbents, and mixed‐mode materials with amine functionalities. A set of 77 small molecules was used to evaluate the columns. We visualized the retention behavior of the different columns using retention time correlation plots. The analytes were classified as cations, anions, or neutral based on their estimated charge under the separation conditions. This involved adjusting the dissociation constants of the analytes for the acetonitrile content of the mobile phase and experimentally determining the pH of the mobile phase containing 70% acetonitrile. The retention correlation plots show that the selectivity differences strongly depended on ionic interactions. Comparisons of the neutral stationary phases (e.g., diol vs. amide) showed more similar selectivity than did comparisons of neutral columns versus columns with cation or anion exchange activity (bare silica or amine columns, respectively). The zwitterionic columns did not behave as perfectly neutral. The correlation plots indicated that they exhibited either cation or anion exchange activity, although to a lesser degree than the silica and amine‐containing stationary phases.
查看更多>>摘要：This paper describes an approach to rapidly and easily calculate the linear solvent strength parameters, namely log k0 and S, under reversed‐phase liquid chromatography conditions. This approach, which requires two preliminary gradient experiments to determine the retention parameters, was applied to various representative compounds including small molecules, peptides, and proteins. The retention time prediction errors were compared to the ones obtained with a commercial HPLC modeling software, and a good correlation was found between the values. However, two important constraints have to be accounted for to maintain good predictions with this new approach: i) the retention factor at the initial composition of the preliminary gradient series have to be large enough (i.e., log ki above 2.1) and ii) the retention models have to be sufficiently linear. While these two conditions are not always met with small molecules or even peptides, the situation is different with large biomolecules. This is why our simple calculation method should be preferentially applied to calculate the linear solvent strength parameters of protein samples.
Wolfgang BickerMarkus KramerWolfgang LindnerMichael L?mmerhofer...
15页
查看更多>>摘要：The present work reports on a novel stable‐bonded amino silica stationary phase obtained by crosslinking of surface aminopropyl moieties using triglycidyl isocyanurate. The obtained cross‐linked amido‐amino network silica material exhibited superior hydrolytic stability compared to classical 3‐aminopropyl phases and showed, inter alia, excellent separation of nine therapeutically effective sulfonamides in hydrophilic interaction/weak anion exchange chromatography elution mode. Additionally, the separation of carbohydrates was investigated under classical hydrophilic interaction chromatography conditions as well proving the suitability of the novel phase for such applications. For the evaluation of the hydrolytic stability the prepared material, as well as two commercially available benchmark columns and a set of in‐house synthesized amino‐modified materials, were exposed to harsh aqueous mobile phase conditions for in total of 50?h at elevated temperature. In this context, the materials were examined by elemental analysis, (13C and 29Si cross‐polarization/magic angle spinning) solid‐state nuclear magnetic resonance, and a chromatographic test before and subsequent to the exposure to these stress conditions. Lastly, the new stationary phase was classified in comparison to a set of commercially available stationary phases by principal component analysis of resultant retention factors gained from chromatographic standard tests.
NSTL
Wiley