Search results for "Selectivity"
showing 10 items of 1148 documents
Influence of template basicity and hydrophobicity on the molecular recognition properties of molecularly imprinted polymers
1996
Abstract Triazine herbicides were used as model templates for a basic study of the molecular recognition process in imprinted polymers. Five structurally related triazine herbicides (atrazine, ametryn, cyanazine, prometryn and terbutylazine) that differ in basicity and hydrophobicity were imprinted. Chromatographic evaluation of the resulting materials in an aqueous-poor mobile phase showed that the selectivity for the template increased with its Bronsted basicity whereas it did not correlate with template hydrophobicity. Thus, the highest and lowest affinity and selectivity for the template was observed using the ametryn-imprinted (p K a =4.1) and the cyanazine-imprinted polymers (p K a =1…
Study of liquid–liquid extraction of ethanol + water azeotropic mixtures using two imidazolium-based ionic liquids
2018
Abstract The present work was focused on the study of two imidazolium-based ionic liquids (ILs) as solvents in liquid–liquid extraction of ethanol from aqueous mixtures. With this aim, the experimental liquid–liquid equilibria (LLE) data of water (1) + ethanol (2) + 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) (3) and water (1) + ethanol (2) + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]) (4) systems were obtained at different temperatures: 283.2, 303.2, and 323.2 K, in order to check the influence of temperature. The results were correlated by non-random two-liquid (NRTL) and universal quasichemical (UNIQUAC) models with good c…
Evaluation of advanced silica packings for the separation of biopolymers by high-performance liquid chromatography
1987
Following previous studies of the use of non-porous monodisperse 1.5-microns n-octyl- and n-octadecyl-bonded silicas in gradient elution of proteins, this work was aimed at elucidating further the properties of this novel column material for peptide and protein separations in comparison with wide-pore silicas. First, it is demonstrated that with short columns (e.g., 35 X 8 mm I.D.) packed with these non-porous reversed-phase materials, mixtures of small peptides and mixtures of proteins can be very efficiently resolved. When the chain length of the bonded ligand was varied, the retention of a test set of proteins in gradient elution followed the ligand sequence C18 greater than C8 approxima…
Solvent selection in liquid chromatography
2017
Many solvents and additives are used to prepare mobile phases in liquid chromatography (LC). Also, mixtures of solvents at different ratios are used to modify the mobile-phase properties. This can make solvent selection for method development a puzzling task, unless suitable guidelines are followed. This chapter summarizes the most common strategies used by skilled chromatographers in reversed-phase, normal-phase, and hydrophilic interaction LC. These are based on considerations about the global polarity of solutes, stationary phase, and mobile phase, which determine the elution strength, and on the particular profile of the contributions of intermolecular interactions to the global polarit…
Solid phase extraction of amines
2005
Abstract The objective of this paper is to provide information about solid phase extraction (SPE) as an alternative to liquid–liquid extraction of amines from several matrices. Different sorbents ranging from non-polar phases, such as C 18 silica to more polar such as cyanopropylsilica (CN) have been tested for analysis of aliphatic amines as monoamines, diamines and polyamines. Phenylalkylamines such as amphetamine or methamphetamine and heterocyclic amines such as histamine or cephalosporins (which also contain a carboxylic group), have also been studied. The different steps involved in the extraction procedure have been tested (conditioning, retention, pre-concentration, washing and elut…
Affinity chromatography with triazine dyes immobilized onto activated non-porous monodisperse silicas
1988
Abstract Non-porous monodisperse silicas with a particle diameter of 2.1 μm were modified with different silanes for immobilization of various triazine dyes including Procion Red HE3B, Procion Red MX5B, and Cibacron Blue F3GA. Lactate dehydrogenase and malate dehydrogenase from different species and aldehyde reductase from rat brain were purified by affinity elution using the substrate of the enzyme and NADH. With Cibacron F3GA the selectivity for NADH-dependent enzymes was higher than with the two Procion dyes. The utility of these immobilized triazine dye systems on non-porous silica supports for the rapid separation of Cohn Fraction III plasma proteins, including plasminogen, is also des…
Modelling of retention behaviour of solutes in micellar liquid chromatography
1997
In micellar liquid chromatography (MLC), the resolution for a given multi-component mixture can be optimized by changing several variables, such as the concentrations of surfactant and organic modifier, the pH and temperature. However, this advantage can only be fully exploited with the development of mathematical models that describe the retention and the separation mechanisms. Several reports have appeared recently on the possibilities of accurately predicting the solute retention in MLC. Although the retention and selectivity may strongly change with varying concentrations of surfactant, organic modifier and/or pH, the observed changes are very regular, and are well described by simple m…
Interpretive optimisation of organic solvent content and flow-rate in the separation of β-blockers with a Chromolith RP-18e column
2009
The chromatographic performance of a Chromolith RP-18e column was comprehensively examined for a group of basic drugs (beta-blockers), eluted with isocratic ACN-water mixtures at increasing flow-rate up to 6 mL/min. As the flow-rate increases at fixed mobile phase composition, peak distribution (selectivity) is maintained, but the relative peak widths increase. This reduces the resolution below satisfactory values for closely eluting compounds. With the monolithic column, flow-rate becomes thus an important factor to be optimised, in addition to the mobile phase composition. Since, theoretically, retention factors (k) are independent of the flow-rate, the classical quadratic model relating …
Resolution assessment and performance of several organic modifiers in hybrid micellar liquid chromatography
2001
The performance of four criteria that measure the elementary resolution (modified selectivity, modified RS, peak purity, and orthogonal valley-to-peak ratio) was critically assessed using as global resolution function, the product of elementary measurements. The peak purities and valley-to-peak criteria yielded the best description of the overall separation according to the shape of the resolution surfaces compared to the peak arrangements in the chromatograms, the capability of defining unambiguously the composition regions of complete resolution, and the resolution achieved in the predicted optimums. Peak purities were used to compare the effect of five organic modifiers (1-propanol, 1-bu…
Protocol to compare column performance applied to hydrophilic interaction liquid chromatography
2019
Abstract The lack of retention of highly polar solutes in liquid chromatography with reversed phase columns (RPLC) can be solved through the use of the hydrophilic interaction liquid chromatographic (HILIC) mode. Due to the complexity of the separation mechanisms in HILIC and the different factors that may have significant influence, the selection of the appropriate stationary phase plays a fundamental role in the development of analytical procedures to obtain good performance. In this work, the chromatographic performance of bare silica and six polar stationary phases with different functionalized groups (with neutral, cationic, anionic and zwitterionic character) are investigated. The beh…