Search results for "Elution"
showing 10 items of 337 documents
Study on resolution capacity and secondary mechanisms of three different TSK gels for organic SEC.
2005
A comparative study on the elution behavior in size-exclusion chromatography (SEC) of three polymeric TSK gel packings, named H, H H R , and H X L types, is performed. The deviations of the universal calibration (u.c.) curves of seven solvent-polymer systems show evidence that the existence of secondary effects accompanying the main SEC mechanism. These secondary mechanisms are a consequence of the binary enthalpic interactions between the different components of the chromatographic system, such as polymer-solvent, polymer-gel and solvent-gel. However, in the present case, the observed deviations from a unique u.c. curve can mainly be attributed to adsorption of polymeric solutes (analytes)…
Solution Properties of Poly-Electrolytes. XI. Adsorption Effects in Aqueous Size-Exclusion Chromatog-Raphy of Polyanions
1994
Abstract Elution profiles of a series of polymer standards such as sodium poly(styrene sulphonate), poly(acrylic acid) and poly(L-glutamic acid) have been obtained from size-exclusion chromatography experiments using separately two types of hydrophilic supports. A variety of mobile phase compositions have been performed to enhance adsorption effects in order to study how this phenomenon can affect to the chromatographic separation mechanism of polyanions. Distribution coefficient values, in general greater than unity, have served to quantify the adsorption effect, as well as to analyze their dependence on eluent ionic strength, on the ionic groups of the support and on the chemical nature a…
Half-width plots, a simple tool to predict peak shape, reveal column kinetics and characterise chromatographic columns in liquid chromatography: Stat…
2013
Peak profiles in chromatography are characterised by their height, position, width and asymmetry; the two latter depend on the values of the left and right peak half-widths. Simple correlations have been found between the peak half-widths and the retention times. The representation of such correlations has been called half-width plots. For isocratic elution, the plots are parabolic, although often, the parabolas can be approximated to straight-lines. The plots can be obtained with the half-widths/retention time data for a set of solutes experiencing the same kinetics, eluted with a mobile phase at fixed or varying composition. When the analysed solutes experience different resistance to mas…
Electrokinetic chromatographic estimation of the enantioselective binding of nomifensine to human serum albumin and total plasma proteins
2012
This report is the first evidence of enantioselective binding of nomifensine to human serum albumin (HSA) and plasma proteins. The overall process with HSA included: (i) consistent experimental design along two independent sessions; (ii) incubation of nomifensine–HSA designed mixtures; (iii) ultrafiltration for separating the unbound enantiomers fraction; (iv) electrokinetic chromatography (EKC) using heptakis-2,3,6-tri-O-methyl-β-cyclodextrin as chiral selector to provide experimental data for enantiomers (first, E1, and second, E2, eluted ones); and (v) a recent direct equation allowing univariate tests and robust statistics to provide consistent parameters and uncertainty. A significant …
Evaluation of the enantioselective binding of imazalil to human serum albumin by capillary electrophoresis
2015
In this work, a methodology for the evaluation of enantioselective binding of imazalil (IMA) enantiomers to human serum albumin (HSA) that does not require the separation of free and bound to HSA fractions is developed. This methodology comprises the incubation of IMA–HSA designed mixtures for 30 min directly in the capillary electrophoresis system and the subsequent direct injection and chiral separation of IMA employing highly sulfated β-cyclodextrin as chiral selector and the complete filling technique. Two mathematical approaches were used to estimate apparent affinity constants (K1), protein binding and enantioselectivity (ES) for both enantiomers of IMA. Moderate enantioselective bind…
Automated determination of clozapine and major metabolites in serum and urine.
1997
Clozapine is an atypical neuroleptic that is increasingly used for the treatment of schizophrenia. An automated method was developed for the routine quantification of clozapine and its major metabolites, N-desmethylclozapine and clozapine N-oxide, in human serum and urine by column switching and online high-performance liquid chromatography with ultraviolet detection. The method included adsorption of clozapine and its metabolites on a cyanopropyl-coated clean-up column (10 microns; 10 mm x 4.0 mm ID), washing interfering serum constituents to waste by deionized water, and, after column switching, separation on C18 ODS Hypersil reversed-phase material (5 microns; 250 mm x 4.6 mm ID). The co…
Gas chromatography/mass spectrometry of catechol estrogens
1992
Abstract Catecholestrogens (CCEs), namely 2- or 4-hydroxyestradiol and hydroxyestrone, are highly polar, reactive, and extremely labile estrogen metabolites in many experimental conditions. For these reasons, indirect assay methods mainly have been used. Some experimental evidence suggests that CCEs are synthesized and biologically active mostly in target cells. At this level, unfortunately, the indirect assays cannot be used. We present a method of gas Chromatographic/mass spectral (GC/MS) analysis for the identification of individual CCEs; the major fragmentation ions of authentic estrogen standards as trimethylsilylether derivatives, and the MS patterns of the major CCEs, namely, 2-hydro…
Determination of fatty alcohol ethoxylates by derivatisation with maleic anhydride followed by liquid chromatography with UV-vis detection.
2007
The esterification of fatty alcohol ethoxylates (FAEs) by melting with maleic anhydride has been studied in the presence of urea. The reaction rate and yield of non-ethoxylated and ethoxylated alcohols increase largely when grinded urea is suspended in the reaction medium, a 100% yield being achieved at 80 degrees C in 15 min. The procedure is tolerant to the presence of large amounts of water. The UV-vis response factors of the derivatives of individual FAE oligomers vary little with the number of carbon atoms in the alkyl chain, n, and the number of ethylene oxide units, m. Derivatised samples of industrial FAE mixtures, cleaning products and river and sea waters were chromatographed on a…
A Qualitative Analysis of Secondary Mechanisms in SEC of Polymers Through the Mean Value of the Viscosimetric Exponent
2001
Abstract Size exclusion chromatography (SEC) universal calibration curves for poly(dimethylsiloxane), polybutadiene and poly(2-vinylpyridine) samples have been obtained in columns packed with cross-linked polystyrene gel using cyclohexane, toluene, benzene, dioxane and tetrahydrofuran as eluents at 25°C. The eluents exhibit different thermodynamic quality for the polymeric solutes and for the gel matrix which is reflected in the values of their Mark-Houwink-Sakurada exponents a. The plots of log(hydrodynamic volume) versus retention volume for the polymeric solutes in different eluents are displaced to higher retention volumes than that of THF-polybutadiene (ideal SEC), evidencing the exist…
An Analysis of the Concentration Effects on Elution Volumes by Using the Preferential Solvation Parameter in Two SEC Packings
2002
Size exclusion chromatography (SEC) elution behavior of different solvent/polymer systems has been analyzed from chromatographic, thermodynamic, and hydrodynamic points of view in two organic column packings based on polystyrene/divinylbenzene (PS/DVB) copolymer, μ-styragel and TSK-Gel H HR . Although both packings present similar chromatographic properties, some differences arise when eluting the same systems. The values of the adsorption distribution coefficients, K p , have been correlated with the preferential solvation coefficient, λ (see Figure), for both packings, showing that those systems with lower and negative λ values (denoting higher preferential solvation of the polymer by the…