Reversed-phase Liquid Chromatography Conditions Research Articles

Comparison of solute descriptors for predicting retention of ionic compounds (phenols) in reversed-phase liquid chromatography using the solvation parameter model

Two solute descriptors that account for the ionization of phenols under reversed-phase liquid chromatographic conditions are compared for the prediction of retention of phenols and neutral compounds at different mobile phase pH values using the solvation parameter model. One of the descriptors is the P descriptor (a scaled effective acid dissociation constant, P=(14−p K*)/10), proposed in a previous work. The other descriptor [log (1− D(1− f)] is based on the degree of ionization ( D) of the phenol and a retention derived parameter ( f) with the value f=10 −1.80 for the chromatographic system studied. Calculation of the P descriptor is straightforward since its value is constant for all mobile phase pH*, but estimation of retention requires a different correlation equation for each mobile phase pH*. In contrast, the log [1− D(1− f)] descriptor is pH* dependent, but it allows the same correlation equation to be used for the estimation of retention at any mobile phase pH*. The D derived descriptor can be successfully applied to the estimation of retention of basic and amphiprotic compounds, for which the P descriptor has yet to be applied.

Conjoint prediction of the retention of neutral and ionic compounds (phenols) in reversed-phase liquid chromatography using the solvation parameter model

The solvation parameter model can be modified to predict the retention of ionized compounds (phenols) under reversed-phase liquid chromatographic conditions by the addition of a further solute descriptor derived from the acid dissociation constant. Two solute descriptors are evaluated for this purpose. The degree of dissociation, D solute descriptor, is defined by Eq. (3), and the scaled effective acid dissociation constant, the P solute descriptor, by (14−p K *)/10. The P solute descriptor provided better predictive accuracy than the D solute descriptor and enabled the retention factor of phenols (log k) to be estimated to 0.1 to 0.2 log units depending on the pH * of the mobile phase. The P solute descriptor is also suitable for use in the conjoint analysis of neutral and ionized compounds with similar predictive accuracy. A significant fraction of the error in retention prediction is due to changes in the solute dipolarity/polarizability π H 2 and effective hydrogen-bond acidity Σ α H 2 accompanying ionization that are not allowed for in the current model.

Surface Diffusion Phenomena in Reversed-Phase Liquid Chromatography with Methanol/Water and Acetonitrile/Water Mixtures

Characteristics of surface diffusion phenomena were studied under low-loading or analytical conditions of reversed-phase liquid chromatography. As mobile phases, methanol/water and acetonitrile/water mixtures were used. In both systems, several similar relationships were confirmed for the enthalpy−entropy compensation effect, the linear free-energy relation, and some correlations between the surface diffusion coefficient, Ds, and mobile-phase composition, φ, and between the ratio of Ds to molecular diffusivity and φ. Similarity of the correlations indicated that the surface diffusion mechanism was essentially identical irrespective of the type of the organic modifiers. A strong influence of φ on Ds was confirmed. A nomograph concerning corresponding mobile-phase compositions for Ds as well as for adsorption equilibrium constant was proposed for the both mobile-phase systems. On the basis of the several correlations, Ds under various conditions in low-concentration systems can be estimated.

Retention behavior of synthetic corticosteroids in packed-column supercritical fluid chromatography

The retention behavior of the synthetic corticosteroids used in a therapy was investigated using packed-column supercritical fluid chromatography (SFC) modified from a commercial liquid chromatographic system. The influence of the stationary phase, modifiers, column pressure and temperature was studied systematically. An aminopropyl-bound silica column and carbon dioxide modified with methanol were selected. The selectivity and separation efficiency in the packed-column SFC were superior to those in the existing normal- and reversed-phase liquid chromatographic conditions. Seven polar corticosteroids, possessing 1 to 4 hydroxyl groups, showed baseline separation within 6.5 min on a modifier gradient.

Ion-pair reversed-phase high-performance liquid chromatography of algal chlorophylls

The Chromatographic behaviour of algal chlorophylls under ion-pair reversed-phase liquid chromatography conditions has been tested either on monomeric and polymeric octadecylsilica columns. Three five-carbon amino compounds (pentylamine, piperidine and pyridine), differing in their molecular shapes and chemical properties, have been used as counterions. The monomeric octadecylsilica column did not allow the separation of chlorophylls c 1 and c 2 with any amine, but separated chlorophyllide a, chlorophyll c 3 and Mg-divinylpheoporphyrin a 5 when pyridinium acetate was used as ion pair agent. The polymeric octadecylsilica column separated chlorophylls c 1 and c 2 with the three counterions, achieving the highest retention and overall separation of acidic chlorophylls when pyridinium was employed as counterion.

Studies on the behaviour of α-, β- and γ-cyclodextrins and some derivatives under reversed-phase liquid Chromatographic conditions

The separation processes of α-, β- and γ-cyclodextrins and their various methyl derivatives have been investigated with Knauer polarimetric (Chiralyser) and refractive index (RI) detectors. RP18 and RP8 hydrocarbon packings and an NH 2 bonded phase were applied as stationary phases. Aqueous methanolic or ethanolic solutions were used as mobile phases. It has been found that the Chiralyser detector response is approximately linear at low concentrations of solutes and that its detection capabilities are about 40 times better than those of the RI detector. Differences in the order of elution of α-, β- and γ-cyclodextrins have been observed for various stationary phases as well as for various mobile phase compositions. The optimal conditions for analytical determinations of cyclodextrins and their derivatives have been discussed.

Kinetics of recombinant human brain-derived neurotropic factor unfolding under reversed-phase liquid chromatography conditions

A model describing the pathway of unfolding of recombinant human brain-derived neurotrophic factor (rhBDNF) under reversed-phase high-performance liquid chromatographic conditions is introduced. The unfolding process is divided into two major steps. The first entails a series of events such as the dissociation of the dimer and the effect of the initial contact of the protein with the stationary phase. The second step is the unfolding of the monomer molecule on the hydrophobic surface exhibiting a rate constant comparable with the time scale of chromatography. The kinetics of rhBDNF unfolding is studied with respect to the type and composition of the organic solvents and as function of the temperature of chromatography. The experimental results validate the suggested multistep unfolding model. The activation energy of monomer unfolding in both solvent systems studied is similar, but the unfolding processes are different in 1-propanol and in acetonitrile.

Conformational changes of brain-derived neurotrophic factor during reversed-phase high-performance liquid chromatography

Recombinant human brain-derived neurotrophic factor (r-HuBDNF) is eluted as two peaks under reversed-phase liquid chromatographic conditions with gradient elution. Sodium dodecyl sulfate polyacrylamide gel electrophoresis confirmed identical molecular weights in the two peaks, while rechromatography of the separated peaks showed interconvertibility. The two peaks are identified as the monomeric forms of the parent molecules. The molecular weight of the components in the peaks was determined by on-line 90° light scattering using a fluorescence detector as a scatterograph. The early eluted peak is a folded form of the r-HuBDNF monomer, while the later eluted peak is an unfolded form of the BDNF monomer. The conformational states were established using a fluorescence detector both at a fixed wavelength and in the scanning mode.

Studies of the surface composition of phenyl and cyanopropyl bonded phases under reversed-phase liquid chromatographic conditions using alkanoate and perfluoroalkanoate esters

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStudies of the surface composition of phenyl and cyanopropyl bonded phases under reversed-phase liquid chromatographic conditions using alkanoate and perfluoroalkanoate estersR. K. Gilpin, Mieczyslaw. Jaroniec, and Shujywan. LinCite this: Anal. Chem. 1991, 63, 24, 2849–2852Publication Date (Print):December 15, 1991Publication History Published online1 May 2002Published inissue 15 December 1991https://doi.org/10.1021/ac00024a008RIGHTS & PERMISSIONSArticle Views58Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (513 KB) Get e-Alerts Get e-Alerts

Solution studies of .beta.-cyclodextrin-pyrene complexes under reversed-phase liquid chromatographic conditions: effect of alcohols as mobile-phase comodifiers

Solution studies of .beta.-cyclodextrin-pyrene complexes under reversed-phase liquid chromatographic conditions: effect of alcohols as mobile-phase comodifiers

Characterization of the surface composition of alkyl bonded phases under reversed-phase liquid chromatographic conditions using homologues of alkanoate and perfluoroalkanoate esters as solute probes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCharacterization of the surface composition of alkyl bonded phases under reversed-phase liquid chromatographic conditions using homologues of alkanoate and perfluoroalkanoate esters as solute probesR. K. Gilpin, M. Jaroniec, and S. LinCite this: Anal. Chem. 1990, 62, 19, 2092–2098Publication Date (Print):October 1, 1990Publication History Published online1 May 2002Published inissue 1 October 1990https://doi.org/10.1021/ac00218a009RIGHTS & PERMISSIONSArticle Views47Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (884 KB) Get e-Alerts Get e-Alerts

Liquid Chromatographic and Mass Spectral Analysis of 1-(3,4-Methylenedioxyphenyl)-1-propanamines: Regioisomers of the 3,4-Methylenedioxyamphetamines

The title 1-(3,4-methylenedioxyphenyl)-1-propanamines represent positional isomers of the N-substituted 3,4-methylenedioxyamphetamines, clandestinely produced drugs frequently encountered by forensic laboratories. These propanamines are prepared by reductive amination of 3,4-methylenedioxypropiophenone with a series of N-alkylamines. Analytical methods are developed to distinguish these compounds from the MDA series. The ultraviolet spectra of the propanamines are very similar to those of the MDAs with absorption maxima at 284 and 236 nm. The propanamines are separated under reversed-phase liquid chromatographic conditions by using a C18 stationary phase and a mobile phase of acidic (pH 3) acetonitrile containing methanol and triethylamine. The relative retention properties of these compounds parallel those observed in the MDA series. The electron impact mass spectra of the propanamines are determined by GC-MS, and the fragmentation pattern clearly distinguishes these compounds from those of the MDA series having the same molecular weight.

Flavonoid glycosides of spore-bearing stems ofEquisetum arvense

In an extract of spore-bearing stems ofEquisetum arvense L. (field horsetail) saponaretin, apigenin 5-glucoside, luteolin 5-glucoside, kaempferol 3-sophoroside, quercetin 3-glucoside, 4-hydroxy-6-(2-hydroxyethyl)-2,2,5,7-tetramethylindanone, and a compound of ketonic nature, isolated previously from an extract of the herbage of the field horsetail, have been identified by high-performance liquid chromatography. The characteristics of the chromatographic behavior of glycosylated flavones under the conditions of reversed-phase liquid chromatography have been studied and it has been shown that the glycosylation of flavones at position 5 of the molecule causes a greater fall in the affinity for a nonpolar stationary phase than in position 7 of the molecule.