Péter Hajós

Retention model for the separation of anionic metal-EDTA complexes in ion chromatography

Abstract A retention model is derived for complex anions eluted from an anion-exchange column with multiple ionic eluents containing hydrogencarbonate, carbonate, and hydroxyl species and the sample solution, containing transition metals, anions and complexing ligand. The theory is based on the generalized ion-exchange equilibrium, protonation and complex-formation equilibria. The unknown parameters of chromatographic ion-exchange equilibrium constants for sample and eluent species are determined from the experimental retention data by iterative minimization, using a non-linear regression algorithm. The model was utilized to predict the retention behaviour of CdEDTA2−, CoEDTA2−, MnEDTA2− and NiEDTA2− ions. The capacity factors of complex ions were determined for wide ranges of pH values and eluent concentrations. Good agreement was obtained between the observed and predicted retentions.

Sample Preparation for the Analysis of Complex Carbohydrates by Multicapillary Gel Electrophoresis with Light-Emitting Diode Induced Fluorescence Detection

This paper evaluates various sample preparation methods for multicapillary gel electrophoresis based glycan analysis to support electrokinetic injection. First the removal of excess derivatization reagent is discussed. Although the Sephadex G10 filled multiscreen 96-well filter plate and Sephadex G10 filled pipet tips enabled increased analysis sensitivity, polyamide DPA-6S pipet tips worked particularly well. In this latter case an automated liquid handling system was used to increase purification throughput, necessary to feed the multicapillary electrophoresis unit. Problems associated with the high glucose content of such biological samples as normal human plasma were solved by applying ultrafiltration. Finally, a volatile buffer system was developed for exoglycosidase-based carbohydrate analysis.

High performance ion chromatography of haloacetic acids on macrocyclic cryptand anion exchanger

A new high performance ion chromatographic method has been developed for the separation of the nine chlorinated-brominated haloacetic acids (HAAs) that are the disinfection by-products of chlorination of drinking water, using a macrocycle-based adjustable-capacity anion-exchange separator column (IonPac Cryptand A1). A gradient method based on theoretical and experimental considerations has been optimized in which 10 mM NaOH-LiOH step gradient was performed at the third minute of the analysis. The optimized method allowed us to separate the nine HAAs and seven possibly interfering inorganic anions in less than 25 min with acceptable resolution. The minimum concentrations detectable for HAAs were between 8.0 (MBA) and 210 (TBA) microg L(-1), with linearity included between 0.9947 (TBA) and 0.9998 (MBA). To increase sensitivity, a 25-fold preconcentration step on a reversed phase substrate (LiChrolut EN) has been coupled. Application of this method to the analysis of haloacetic acids in real tap water samples is illustrated.

Ion chromatographic separation of car☐ylic acids prediction of retention data

Abstract The retention behavior of biologically relevant monovalent (formic, acetic, propionic, lactic and pyruvic) and divalent (oxalic, malonic, succinic, fumaric, maleic and tartaric acids) car☐ylic acids together with inorganic analytes (chloride and sulphate) has been studied. The separation was performed on a latex-based strong anion-exchange resin using carbonate buffer systems in suppressed IC. The retention behaviour of analytes was investigated at different pH values and [HCO 3 − ]+[CO 3 2− ] concentrations. A theoretical model, involving ion-exchange equilibria of sample and eluent anions, was derived and applied to the chromatographic data obtained. Chromatographic ion exchange selectivity values were determined and retention data were calculated for the anions using different carbonate eluent conditions. The average of errors between the predicted and the measured retention volumes of the analytes studied does not exceed 4.0%. The study effectively characteristics the behaviour of different analytes under elution conditions of practical importance.

Mixed-mode liquid chromatography of carboxylic acids and inorganic anions on a latex-based pellicular stationary phase

Abstract The retention behaviour of mono-, dicarboxylate and inorganic anions on latex-based pellicular anion-exchanger was investigated. This paper is focused on the possible retention mechanism providing a retention database on a variety of mobile phase compositions. It has been demonstrated that anions can interact with the cation-exchange layer on the highly crosslinked latex-based pellicular phase as well as with the anion-exchange sites. A hypothesis is proposed to explain a mixed-mode retention of the series of analytes. A combination of two mechanisms has been found responsible for the enhanced selectivity: ion-exchange and ion-exclusion. Applications include the separation of formate, acetate, propionate, lactate, pyruvate, oxalate, malonate, succinate, tartrate, fumarate, maleate , chloride, nitrate and sulphate with NaOH eluent using suppressed conductivity detection. The study effectively characterizes the behaviour of different analytes under elution conditions of practical importance.

Preparation and ion chromatographic application of surface-sulphonated cation exchangers

Summary Low-capacity (0.007–0.500 mequiv./g) surface-sulphonated cation exchangers can be produced from unswollen polystyrene-divinylbenzene copolymers. The optimal sulphonation conditions were determined. The applicability of the resin was demonstrated by the ion chromatographic separation of Li + and K + ions. The homogeneity of the surface of the resin was proved by scanning electron micrographs and by determining the sulphur distribution by X-ray analysis.

Histidine as a dipolar eluent component in cation chromatography

Abstract Acidified l -histidine [2-amino-3-(4-imidazolyl)propionic acid] was found as an eluent in membrane-suppressed cation chromatography. Both mono- and divalent cations such as alkali and alkaline-earth metals can be separated by simple isocratic chromatography using conductivity detection. The effect of eluent pH and concentration on the retention was determined. The elution and suppression behavior can be easily governed by the pH of the mobile phase. The eluent exists as the divalent driving cation at lower a pH than 2, with the ability to elute strongly retained ions, and has very low conductivity background at the pH of the isoelectric point of histidine. Results are compared with another combination of 2,3-diamino-propionic acid eluent as a dipolar component. The applicability of the phase system is demonstrated by the analysis of a high purity water sample.

Effect of stationary phase hydrophobicity and mobile phase composition on the separation of carboxylic acids in ion chromatography

In a previous work, we studied the retention behavior of monovalent and divalent carboxylic acids on a highly cross-linked polystryene-divinylbenzene anion-exchange column (IonPac AS4A-SC) using a carbonate-based buffer, and a retention model was applied to the chromatographic data obtained. In this work we characterized the retention of carboxylates (formic, acetic, propionic, lactic, pyruvic, oxalic, malonic, succinic, fumaric, maleic, tartaric, glutaric, adipic, malic, mucic, trans-beta-hydromuconic, trans,trans-muconic acids) on a column with higher hydrophilicity (IonPac AS11) according to analyte and stationary phase properties, using previously investigated eluent compositions and comparing the retention data obtained. Moreover, the effect of organic modifiers (CH3OH and CH3CN) in the eluent on the retention factors was also evaluated. The chromatographic data obtained on the IonPac AS11 column were fitted by the retention model and allowed one to obtain and to compare ion-specific selectivity constants (parameters of the model) with the ones obtained with the previous column.

Studies on the retention behaviour of metal-EDTA complexes in cation chromatography

Abstract Separation of metal-EDTA complexes (e.g. with Cu 2+ , Ni 2+ and Pb 2+ ) has been carried out with a cation-exchange polymer based column. Two mobile-phase systems, containing either nitric or perchloric acid, have been studied and the metal complexes with EDTA have been detected by UV spectrophotometry. A retention model has been developed. It takes into account both ion-exchange and adsorption phenomena of all positive, neutral and, as an attempt, negative metal-EDTA species. The ion-exchange behaviour of the metal-EDTA complexes and the adsorption effects due to neutral species have been applied for an on-line preconcentration procedure.

High performance ion chromatography of transition metal chelate complexes and aminopolycarboxylate ligands

A simple ion chromatographic method was developed for the separation of transition metal chelates (CuEDTA, CuDCTA, ZnEDTA, ZnDCTA) and free anionic complexing ligands (EDTA, DCTA) using alkaline carbonate eluents and conductivity detection. The complex equilibria and kinetic process of separations were studied in order to understand major factors in the control of selectivity and retention order of complex anions. A systematic study was applied to identify the additional peaks of the system as NaEDTA(3-), NaHEDTA(2-), Na(2)EDTA(2-), EDTA(4-)/HEDTA(3-), DCTA(4-)/HDCTA(-3). On the basis of microequilibrium considerations of chelating ligand, it was shown that one should expect the peaks of sodium chelates when the ligand is in excess in the sample solution. The probability density function was introduced for calculation of complex chromatograms, because complexing ligands can exist in at least two different interconvertible forms in the presence of metal ion. The chromatogram of interconverting chelate species can be given as the sum of probability density functions (P) weighed by the molar fractions of complexed (Φ(ML)) and dissociated (Φ(L)) forms. The influences of kinetic rate of complex formation and dissociation on the distribution of components between eluents and ion exchange stationary phases were quantitatively described and demonstrated by elution profiles. The applicability of the developed method is represented by the simultaneous analysis of transition metal chelates and inorganic anions. ICP-AES analysis and FTIR-ATR technique were used for confirmation of IC results for metals and ligands, respectively. Collection protocols for the heart-cutting procedure of chromatograms were applied in the analysis of target components. The limit of detection and linearity of the method in the range of 0.01-0.25 mM sample concentration were also presented.