Reversed-phase Ion-interaction Chromatography Research Articles

Investigation of the retention/pH profile of zwitterionic fluoroquinolones in reversed-phase and ion-interaction high performance liquid chromatography

The retention/pH profiles of three fluoroquinolones, ofloxacin, norfloxacin and ciprofloxacin, was investigated by means of reversed-phase high performance liquid chromatography (RP-HPLC) and reversed-phase ion-interaction chromatography (RP-IIC), using an octadecylsilane stationary phase and acetonitrile as organic modifier. Sodium hexanesulphonate and tetrabutylammonium hydroxide were used as sources of counter ions in ion-interaction chromatography. The retention/pH profiles under in RP-HPLC were compared to the corresponding lipophilicity/pH profiles. Despite the rather hydrophilic nature of the three fluoroquinolones positive retention factors were obtained while there was a shift of the retention maximum towards more acidic pH values. This behavior was attributed mainly to non-hydrophobic silanophilic interactions with the silanized silica gel material of the stationary phase. In ion-interaction chromatography the effect of counter ions over a broad pH range was found to be ruled rather by the ion pair formation in the mobile phase which led to a drastic decrease in retention as a consequence of the disruption of the zwitterionic structure and thereupon the deliberation of a net charge in the molecules. At pH values at which zwitterionic structure was not favored both the ion-exchange and ion pair formation mechanisms were assumed to contribute to the retention.

HPLC Separation of Diastereomeric Metal Complexes of the Form Δ,Λ-[Ru(diimine)2(S)-aminoacidate

Complete separation of the photosensitive diastereomeric complexes of the general form [Ru(diimine)2(S)-aminoacidate], in which the diimine is 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy) and S-amino or N-methyl-S-aminoacidate are S-aspartate, S-tryptophanate or N-methyl-S-tryptophanate, has been achieved by reversed-phase ion-interaction chromatography. This has allowed the photo-equilibrated isomeric ratios for each complex to be estimated.

Preconcentration and separation of haloacetic acids by ion chromatography

A comparative study was made of the chromatographic behaviour of five haloacetic acids (mono-, dibromoacetic and mono-, di-, trichloroacetic acids). The techniques investigated included reversed-phase ion interaction chromatography with UV detection, suppressed and non-suppressed anion-exchange chromatography. The systems are discussed studying the retention as a function of the mobile phase parameters and the stationary phases used (LiChrospher 100 RP-18, IonPac AS9, AS10 and AS11). A preconcentration step, performed on different substrates, namely LiChrolut-EN and activated vegetal carbon, has been optimized in order to reduce the method detection limits. Results obtained for drinking water samples are shown.

Retention Model for Anionic, Neutral, and Cationic Analytes in Reversed-Phase Ion Interaction Chromatography

A model for the prediction of retention data for 1- and 2-charged analytes in ion interaction chromatography, previously developed by our group, has been extended to account for the retention behavior of cationic and neutral analytes. By using a single mathematical procedure, it is possible to develop applicative equations to describe the simultaneous effect of the concentration of ion interaction reagent, organic modifier, and counterion on the capacity factor k‘ of analytes with different charges (neutral, negative, and positive). The modeling considers the retention process as a result of several adsorption and ion exchange equilibria, whose constants can be calculated by an iterative method of nonlinear regression. The applicability of the equation developed has been tested on different classes of organic (aromatic sulfonates and carboxylic acids) and inorganic analytes. The experimental design has been planned in order to describe the chromatographic behavior as a function of the mobile phase components: cetyltrimethylammonium chloride, sodium chloride, and methanol.

Temperature Dependence of Retention in Reversed-Phase Ion-Interaction Chromatography

The dependence of retention on temperature in reversed-phase ion-interaction chromatography is investigated. 5mM octylammonium o-phosphate in aqueous solution is used as the interaction reagent, and retention of analytes characterized by different chemical properties is considered in the temperature range of 25-55°c. Variation of the thermodynamic parameters of enthalpy and entropy for the transfer process of the solute from the mobile to the stationary phase are evaluated. The results indicate that the retention process proceeds in the temperature range investigated through only a single mechanism and that similar retention mechanisms characterize all the analytes studied, independent of their chemical structure.

The Role of pH of the Mobile-Phase in Ion-Interaction RP-HPLC

The dependence of retention on pH of the mobile phase is investigated in reversed-phase ion interaction chromatography, being the mobile phase an aqueous solution of 5.0 mM octylammonium and ortho-...

Retention of Anions as a Function of Mobile Phase PH in Ion-Interaction RP-HPLC

Abstract Retention of typical anions as a function of pH of the mobile phase in reversed-phase ion-interaction chromatography was studied. The different behaviours observed for anions of acids characterized by different pKa values were discussed, in comparison with literature results obtained in reversed-phase and in reversed-phase ion-pair chromatography.

Separation of metal-cyanide complexes by reversed-phase ion-interaction high-performance liquid chromatography

Reversed-phase ion-interaction chromatography has been used to study the separation of Cu(I), Ag(I), Ni(II), Au(I), Co(III), Fe(III), and Fe(II) cyano complexes on silica and carbon-based reversed-phases with UV detection at 215 nm. Separation of the metal-cyanide complexes was affected by a number of experimental factors including the nature and concentration of the organic modifier, nature and concentration of the ion-pairing reagent, pH, and ionic strength of the mobile phase. Differences between the elution order of metallo-cyanides observed in the present work and in other investigations under similar experimental conditions are explained by a difference in the ionic strength of the mobile phase. Finally, this technique is used to analyze metal-cyanide complexes in a gold mill solution.

Sulfate determination in lagoon water (venice) by reversed-phase ion-interaction chromatography ? a method validation

The validation of a new ion-interaction chromatographic method for sulfate determination is presented by the comparison with results obtained by ionchromatography. The two procedures were employed to quantify sulfate in model solutions and in samples of Venice lagoon water. The statistical t-test for multiple samples showed no significant difference between the two methods, at the 99% confidence level.

Separation of some metals as their anionic oxalate complexes by reversed-phase ion-interaction chromatography

The separation of some metal cations in the form of their oxalate complexes was investigated in a reversed-phase system with tetrabutylammonium cation

Reversed-phase ion-interaction chromatography of metal ions by EDTA precomplexation

Conditions for the isocratic separation by reversed-phase ion-interaction chromatography of Bi(III), Fe(III), Co(III), Ni(II), Cu(II) and Pb(II) chelates with ethylenediaminetetraacetic acid have been studied using UV-Vis detection. Both chromatographic and spectrophotometric conditions for the determination of these metal chelates are discussed including ion-interaction reagent concentration, water/methanol ratio, ionic strength, pH and absorbing wavelengths. Detection limits are particularly satisfactory for Bi(III), Fe(III) and Co(III) chelates.

Determination of melatonin and monoamines in rat pineal using reversed-phase ion-interaction chromatography with fluorescence detection

A method is reported for the ion-interaction, reversed-phase separation of 24 compounds (chiefly monoamines) arising from the metabolism of tyrosine and tryptophan. These compounds were separated as two groups. The first group comprised 3,4-dihydroxyphenylethylene glycol, tyrosine, 3-methoxy-4-hydroxyphenyl glycol, 5-hydroxytryptophan, norepinephrine, 3,4-dihydroxyphenylacetic acid, epinephrine, 5-hydroxyindole-3-acetic acid, homovanillic acid, 5-hydroxytryptophol, dopamine, tryptophan. N-acetylserotonin, N-acetyltryptophan, 5-methoxytryptophan and serotonin. The mobile phase consisted of a 6.8:93.2 (v/v) mixture of acetonitrile and an aqueous solution containing 0.16 M ammonium phosphate, 0.06 M citric acid, 0.15 mM disodium EDTA, 10 mM dibutylamine and 6 mM sodium 1-octanesulphonate at pH 4.50. The second group of compounds comprised 6-hydroxymelatonin, 5-methoxyindole-3-acetic acid, indole-3-acetic acid, 5-methoxytryptamine, tryptamine, 5-methoxytryptophol, melatonin and tryptophol. The mobile phase consisted of a 16:84 (v/v) mixture of acetonitrile and an aqueous solution containing 0.05 M ammonium phosphate, 0.05 M citric acid, 0.15 mM disodium EDTA, 25 mM dibutylamine and 5 mM sodium 1-octanesulphonate at pH 5.30. Detection was by fluorescence measurement (lambda ex = 280 nm, lambda em = 340 nm). The proposed method exhibited linear calibration over the biochemically significant concentration range, with detection limits in the 10-200 pg range. Excellent precision for peak areas and retention times was observed, even over a period of 24 h. The applicability of amperometric detection (at 0.72V) is also demonstrated. The method is applied to the determination of monoamines in individual rat pineals. Low nanogram levels of tyrosine, norepinephrine, 5-hydroxyindole-3-acetic acid, tryptophan, serotonin and 6-hydroxymelatonin, and picogram levels of 5-hydroxytryptophan, 5-hydroxytryptophol, 5-methoxyindole-3-acetic acid, indole 3-acetic acid, 5-methoxytryptophol and melatonin were indicated in most of the samples.

Simultaneous determination of creatinine, uric, L(+)-ascorbic and orotic acids in milk by reversed-phase ion-interaction HPLC chromatography

Separation methods have been developed by means of reversed-phase ion-interaction HPLC chromatography, using octylamine ortho-phosphate as the interaction reagent. In particular the separation of some antioxidants of relevant interest (known also as radical scavengers) such as L(+)-ascorbic acid, uric acid, orotic acid and cysteine, as well as the separation of creatine and creatinine have been performed. The results have been applied to the analysis of different kinds of milk, namely a dairy farm milk, a commercial whole fresh milk and a UHT-sterilized one: creatinine, uric, L(+)-ascorbic and orotic acids were identified and quantified.

Factors Influencing the Resolution of Positionally Isomeric Alkane Monosulfonates in Reversed-Phase Ion-Interaction Chromatography with Indirect Photometric Detection

L'effet des parametres influencant la selectivite en chromatographie a interaction d'ions est etudie pour separer des decanemonosulfonates, isomeres de position. L'optimisation des parametres tels que les reactifs choisis (le chlorure de methylpyridinium, le sulfate de cuivre), la temperature, revele l'efficacite considerable de la methode pour des applications analytiques

Multifactor simultaneous statistical optimization of the mobile phase composition for the separation of inorganic anions in reversed-phase ion-interaction chromatography

The optimization of the analysis of a mixture of five anions with reversed-phase ion interaction chromatography has been investigated. The criteria selected were the resolution of the most critical peak pair, R s1 (NO − 2-Br −), the total analysis time which corresponds to a certain range of R s2 (NO − 3-SO 2− 4) and the peak height of Cl −, NO − 3 and SO 2− 4. The factors selected to realize the optimization were the mobile phase concentrations of tetrabutylammonium iodide and phthalate buffer, and the pH. Only a limited number of experimental data points, ordered in a central composite design, were required for the computation of the response function with a non-linear regression model. Application of this computer-aided multifactor simultaneous statistical approach resulted in a rapid optimization of the selected criteria. The computed global optimum is close to the best experimentally obtained result.

Retention and separation of inorganic anions by reversed-phase ion-interaction chromatography on octadecyl silica

The retention behaviour of chloride, nitrite, bromide, nitrate and sulphate was investigated using Partisil 10 ODS-3 as the stationary phase and a solution of tetrabutylammonium in aqueuos phthalate or phosphate buffer as the eluent. The quaternary ammonium ion adsorption behaviour and the influence of the quatenary ammonium concentration, the pH and the buffer concentration on the retention of the inorganic anions is discussed. The major adsorption and ion-exchange equilibria in the retention process were studied and used to develop a retention model for the different analytes. This retention model was verified experimentally. Ion-interaction reversed-phase chromatography with an octadecyl-bonded silica stationary phase and tetrabutylammonium iodide—phthalate eluent was found to be successful system for the separation and determination of inorganic anions and when conductivity detection is used.

Trace determination of sulfide by reversed-phase ion-interaction chromatography using pre-column derivatization

Trace determination of sulfide by reversed-phase ion-interaction chromatography using pre-column derivatization

Trace determination of sulfide by reversed-phase ion-interaction chromatography using pre-column derivatization

Analyse de traces de sulfure apres une reaction avec le N,N-dimethylphenylenediamine-1,4 pour former le bleu de methylene

Reversed-phase ion-interaction chromatography of leukotrienes, lipoxins and related compounds

A novel mobile phase containing heptafluorobutyric acid has been used for ion-interaction high-performance liquid chromatography of leukotrienes, lipoxins and related compounds on octadecyl-silane silica columns. The use of a hydrophobic perfluorinated carboxylic acid as an ion-interaction agent at optimized concentration and pH permitted rapid, isocratic separation of leukotrienes, lipoxins and monohydroxyeicosatetraenoic acids. A completely volatile mobile phase suitable for preparative chromatography was obtained by using triethylamine as the base for pH adjustment. With this novel mobile phase, leukotrienes and monohydroxyeicosatetraenoic acids were completely separated in less than 15 min.

Computer-assisted selection of mobile phase composition in reversed-phase liquid chromatography : Definition of the optimisation search area

In order to reduce the time required for successful implementation of computer-assisted methods for the selection of the optimal mobile phase composition in reversed-phase liquid chromatography, it is desirable to limit the range of the mobile phases that are to be considered. This is conventionally achieved by defining an optimisation search area bounded by isoeluotropic binary mobile phases of water with methanol, acetonitrile or tetrahydrofuran. This process requires the use of equations (or “transfer rules”) relating the eluotropic strengths of these three organic modifiers. By reference to the separation of seven amines by reversed-phase ion-interaction chromatography, published transfer rules are shown to be unreliable as a means of calculating isoeluotropic mobile phases. New transfer rules were derived for a small group of structurally related amines, and use of these rules to define the optimisation search area gave improved performance of the optimisation process. Nevertheless, these new transfer rules also showed considerable error in predicting isoeluotropic mobile phases. It is concluded that the optimisation search area is best established empirically, using transfer rules initially to estimate isoeluotropic mobile phase compositions, followed by experimentation to confirm that the mobile phases selected are isoeluotropic. When this approach was applied- to the isocratic separation of ten fat-soluble vitamins, excellent results were obtained.