Ákos Bartha
Delft University of Technology
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Featured researches published by Ákos Bartha.
Journal of Chromatography A | 1984
Ákos Bartha; Gy. Vigh; Hugo A.H. Billiet; L. de Galan
Abstract Adsorption isotherms of straight chain sodium alkanesulphonates (from butane to octane) were determined by the breakthrough method in aqueous phosphate buffer on ODS-Hypersil, along with retention data of similarly and oppositely charged ionic and non-ionic solutes. The effects on the solute retention of the chain length of the pairing ion were examined both at varying and constant counter ion (sodium) concentrations, in terms of both the mobile phase and stationary phase pairing ion concentrations. A practical consequence of the use of systems with constant counter ion concentration is that pairing ions with different chain lengths (members of a homologous series) are interchangeable in terms of their surface concentrations.
Journal of Chromatography A | 1983
Ákos Bartha; Gy. Vigh
Abstract The adsorption isotherms of symmetrical tetraalkylammonium ion-pair reagents (tetramethyl, tetraethyl, tetrapropyl and tetrabutyl) on LiChrosorb RP-18 in 25 mM H3PO4NaH2PO4 aqueous buffer were determined from breakthrough curves at a constant Br− counter ion concentration of 200 mM, maintained by the addition of sodium bromide. The Langmuir and Freundlich isotherms were tested with the data and a poor fit was observed at higher mobile phase concentrations. The adsorption isotherms of tetrabutylammonium bromide were measured in the same system, in 0–70% (v/v) methanol—aqueous buffer eluents, at seven eluent compositions. Stationary phase ion-pair reagent concentration versus methanol concentration (at constant mobile phase pairing ion concentrations), and stationary phase versus mobile phase pairing ion concentration (at constant methanol concentrations) plots were obtained. With these plots, pre-selected stationary phase ion-pair reagent concentrations can be set (either held constant or varied according to a programme) under widely varying chromatographic conditions.
Journal of Chromatography A | 1984
Ákos Bartha; Hugo A.H. Billiet; Leo de Galan; Gyula Vigh
Abstract Adsorption isotherms of sodium 1-butanesulphonate and retention data of both positively and negatively charged ions have been determined in the presence and absence of sodium bromide, in aqueous phosphate buffer, on ODS-Hypersil. Large differences are found in the retention of ionic solutes when the concentration of the pairing ion in the mobile phase is increased over the same range with constant or changing counter ion concentration. Retention maxima are observed for positively charged ions when the pairing ion and the counter ion concentrations increase simultaneously, but not when the counter ion concentration in the eluent is kept constant at a high value. A unifying picture is given for the retention of oppositely charged solutes in terms of the ratio of the concentration of the adsorbed pairing ion and the mobile phase concentration of the counter ion, Ps/Cm.
Journal of Chromatography A | 1988
Peter J. Schoenmakers; Joost K. Strasters; Ákos Bartha
Abstract The resolution function is commonly used to describe the extent of separation between successive peaks in a chromatogram. However, the resolution is usually defined in such a way that it is applicable only to symmetrical (Gaussian) peaks. Moreover, the resolution does not provide a realistic estimate of the extent of separation between two peaks with greatly different areas. Nevertheless, the main advantage of the resolution is that its value can be predicted from retention and efficiency data for the individual peaks. Simple methods are described to correct the resolution function for (i) large variations in peak areas and (ii) peak asymmetry. The corrections are derived as modifications of the resolution equation. An important consequence of these modifications is that the resolution for a pair of peaks has two different values, one for each peak. The new resolution equations were evaluated using computer-generated (exponentially modified Gaussian) peak profiles. The effects of varying degrees of peak asymmetry and varying peak-area ratios were studied.
Journal of Chromatography A | 1983
Ákos Bartha; Gy. Vigh
Abstract The retention of positively and negatively charged ions, as well as of neutral solutes, was studied in 0–70% methanol in 25 mM aqueous phosphate buffer (pH 2.1–3.4) eluents as a function of the tetrabutylammonium bromide ion pair reagent concentration. The log k′ vs. mobile phase pairing ion concentration (Pm) plots (which showed Pm- and [methanol]-dependent maxima) could be transformed into log k′ vs. stationary phase pairing ion concentration (Ps) curves by using the simultaneously determined adsorption isotherms of tetrabutylammonium bromide. While the shape of the log k′ vs. Pm curves of oppositely charged solutes changed considerably with the concentration of methanol in the eluent, the log k′ vs. Ps curves were more similar, and their maxima are in the 80–120 μmole/g range. The log k′ vs. Pm curves of similarly charged solutes were more alike. The methanol concentration of the eluent influences the retention of oppositely charged solutes more sensitively than that of the similarly charged solutes. At constant Pm the log k′ vs. [methanol] curves of oppositely charged solutes were S-shaped, while the log k′ vs. [methanol] curves at constant Ps values ran similar to the log k′ vs [methanol] curves obtained in the absence of ion-pairing reagents.
Journal of Chromatography A | 1988
Jan Ståhlberg; Ákos Bartha
Abstract To understand the mechanism of ion-pair chromatography, a correct description of the adsorption isotherm of the amphiphilic modifier is important. The adsorption isotherms of butyl-, hexyl- actylsulphonate were investigated according to the concepts of the electrostatic theory of ion-pair chromatography. This theory was also extended to include the simultaneous effect of surface potential and competition between the amphiphile and the analyte for the available surface area. It was found that there is good agreement between the theory and experimental results.
Chromatographia | 1985
Ákos Bartha; Gy. Vigh; Hugo A.H. Billiet; L. de Galan
SummaryThe retention of positively and negatively charged and neutral solutes was studied in an aqueous phosphate buffer eluent, with constant inorganic-counterion concentration, on ODS-Hypersil stationary phase in the presence of various sulfonic acid ion-pairing reagents. The adsorption isotherms of the ion-pairing reagents d-camphor-10-sulfonic acid, sodium cyclohexylsulfamic acid and sodium alkylsulfonates (butyl-, hexyl- and octyl-) were determined by the breakthrough method.
Journal of Chromatography A | 1989
Gary K.-C. Low; Ákos Bartha; Hugo A.H. Billiet; Leo de Galan
Abstract Separation selectivity of ionized solutes in reversed-phase ion-pair chromatography can be varied by manipulating a number of mobile phase variables. From a study of computer-simulated mixtures of differently charged solutes it became obvious that the selection of the parameter space for systematic solvent optimization is constrained principally by the nature of the charged species present in the mixture. For most sample mixtures there are preferred combinations of the mobile phase variables, leading to a significant reduction of the optimization search area. A systematic strategy is shown here for the determination of the charge type and the relative retention (hydrophobicity) of the components in samples for which this information is not known. The first part of the strategy identifies the weak acids and bases according to their retention behavior in two gradient separations at pH 2.5 and 7.5, respectively. The second part determines the presence of strong acids and bases by the same two gradients but “pulsed” with a negatively and a positively charged ion-pairing reagent, respectively. Solutes are classified according to their characteristic retention shifts using a sequential-elimination scheme. Solutes without retention shifts are classified as non-charged solutes.
Journal of Chromatography A | 1990
Ákos Bartha; Jan Ståhlberg
Abstract Based on the electrostatic model of reversed-phase ion-pair chromatography, a practical equation was developed to describe the relationship between the capacity factor of ionic solutes and the eluent concentration of the amphiphilic pairing ion. At constant ionic strength and organic modifier concentration, the logarithm of solute capacity factor can be approximated as a linear function of the logarithm of the pairing ion concentration. The slope of this relationship is determined by the sign and number of charges of the solute ion and the pairing ion. The limitations and the practical use of the proposed model are discussed in detail.
Journal of Chromatography A | 1990
Joost K. Strasters; Frank Coolsaet; Ákos Bartha; Hugo A.H. Billiet; Leo de Galan
Abstract A peak tracking strategy based on multivariate analysis of multiwavelength spectral data was applied to four chromatograms of a mixture of eight local anaesthetics and extended to cope with coelution of components having identical spectral characteristics. The resulting characterization of the retention behaviour of the individual components was used to select a suitable parameter space for the subsequent improvement of the observed separation.
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Commonwealth Scientific and Industrial Research Organisation
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