bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of electrolyte nature on the separation selectivity of amphetamines in nonaqueous capillary electrophoresis: Protonation degree versus ion pairing effects
Authors: Descroix Stéphanie , Varenne Anne , Geiser Laurent , Cherkaoui Samir , Veuthey Jean‐Luc , Gareil Pierre 
Published: May 2003

AbstractThe simultaneous analysis of Ecstasy and its derivatives in an acetonitrile‐methanol (80:20 v/v) mixture was previously shown to be strongly dependent on the nature of the electrolyte (acetate versus formate). To elucidate the phenomena involved, systematic experiments were conducted in this solvent medium. Conductivity measurements allowed to evaluate the ion‐pairing rate in the background electrolyte (BGE) and thereby distinguish between electrolyte concentration and ionic strength. The influence of electrolyte concentration on analyte effective mobilities (μeff) was studied by capillary electrophoresis (CE). As μeff extrapolated to infinite dilution proved to be independent of the nature of the electrolyte, selectivity changes could not be attributed to a modification in the protonation degree of amphetamines. Experimental mobility data were then confronted to existing theoretical mobility models to discriminate between ion pairing or simple ionic strength effect. Ion‐pair formation in a BGE containing acetate was highlighted with an ion‐pairing model and ion‐pair formation constants between each amphetamine and acetate ion were calculated.
The principles of migration and dispersion in capillary zone electrophoresis in nonaqueous solvents
Authors: Porras Simo P. , Riekkola Marja‐Liisa , Kenndler Ernst 
Published: May 2003

AbstractNonaqueous solvents are interesting media for capillary zone electrophoresis as they can affect all relevant parameters governing the separation of sample zones. However, for a rational planning of the working conditions and an appropriate interpretation of the results obtained, the basic principles of ion migration and zone dispersion must be understood. Many solvent induced effects need to be carefully considered and recognized before full exploitation of nonaqueous solvents can take place. It is the goal of this overview to present the fundamental physicochemical aspects of capillary zone electrophoresis in nonaqueous solvent systems. Therefore, the detailed discussion is related to the effect of organic solvents on electrophoretic mobilities (based on the theory of conductance), acid‐base dissociation behavior (based on the transfer activity coefficient and medium effect), pH, separation efficiency (with regard to mobility and diffusion coefficient in dilute solutions), resolution, and electroosmotic flow.
Enantioselective strong cation‐exchange molecular recognition materials: Design of novel chiral stationary phases and their application for enantioseparation of chiral bases by nonaqueous capillary electrochromatography
Authors: Constantin Stéphane , Bicker Wolfgang , Zarbl Elfriede , Lämmerhofer Michael , Lindner Wolfgang 
Published: May 2003

AbstractNew chiral stationary phases derived from enantiomerically pure derivatives of cysteine carrying sulfonic acid groups are synthesized and evaluated for enantiomer separation of chiral bases by non aqueous capillary electrochromatography after bonding to a linker and grafting upon thiol‐modified silica particles. Structural modifications of these low molecular weight chiral selectors are investigated and discussed in terms of apparent enantioselectivities and resolution factors based on the enantiomeric separations of a set of chiral bases including β‐blockers, β‐sympathomimetics and other basic drugs. The influence of the mobile phase constitution and its flow velocity on the enantioseparation by nonaqueous capillary electrochromatography is also briefly evaluated and discussed for the chiral substances investigated.
Heteroconjugation‐based capillary electrophoretic separation of phenolic compounds in acetonitrile and propylene carbonate
Authors: Kuldvee Ruth , Vaher Merike , Koel Mihkel , Kaljurand Mihkel 
Published: May 2003

AbstractA mixture of methyl‐ and hydroxy‐substituted phenols was separated by capillary electrophoresis in pure acetonitrile and propylene carbonate. Interactions between undissociated phenolic compounds and the background electrolytes were investigated. In the present work, benzyltriethylammonium chloride, tetrabutylammonium acetate, and two room temperature‐molten salts, 1‐butyl‐3‐methyl imidazolium trifluoroacetate and 1‐butyl‐3‐methyl imidazolium heptafluorobutanoate, were used as background electrolytes. The formation of a negative complex between background electrolyte anion and neutral phenolic compound was observed and the formation constant calculated. The formation constants for anion‐analyte complexes were approximately the same in propylene carbonate and in acetonitrile. In both solvents the formation constants were the highest for acetate and the lowest for trifluoroacetate. The separation of analytes was slightly influenced by the nature of the solvent: in acetonitrile the resolution between peaks was higher for 1,3‐dihydroxyphenol and 1,3,5‐trihydroxyphenol, in propylene carbonate 3‐methylphenol and phenol were better separated. It was demonstrated that traces of water influence the mobilities of anion‐phenol complexes in propylene carbonate.
Solvent effects in microemulsion electrokinetic chromatography
Authors: Klampfl Christian W. 
Published: May 2003

AbstractThe contribution of organic solvents to the mechanisms responsible for separation in microemulsion electrokinetic chromatography (MEEKC) is reviewed. Organic solvents are needed as constituents of microemulsions for a series of reasons. (i) A water‐immiscible organic substance is used to form the actual oil phase of the microemulsion, (ii) a less hydrophobic solvent is commonly employed as a so‐called cosurfactant, and (iii) in many cases an organic modifier is added to influence the solubility of the analytes in the aqueous phase of the microemulsion. All these organic solvents do not only participate in the separation in their actual function, but also interact with each other and the analytes. Variations in separation selectivities triggered by changes in the nature and/or concentration of these organic solvents present in microemulsions suitable for MEEKC are discussed in this work.
Capillary electrophoretic study of the binding of zinc(II) ion to bacitracin A1 in water‐2,2,2‐trifluoroethanol
Authors: Castagnola Massimo , Rossetti Diana Valeria , Inzitari Rosanna , Vitali Alberto , Lupi Alessandro , Zuppi Cecilia , Cabras Tiziana , Fadda Maria Benedetta , Podda Ilaria , Petruzzelli Raffaele , Giardina Bruno , Messana Irene 
Published: May 2003

AbstractBinding of Zn2+ to bacitracin A1 was studied by capillary electrophoresis in water/2,2,2‐trifluoroethanol (70/30 v/v) at different apparent pH values in order to estimate the association constant of metal, the acidic dissociation constants and the Stokes radii of both free and bounded peptide in apolar environment. The Stokes radii of the free peptide species were compared with those in aqueous solution, as obtained in a recent study performed by our group, indicating that apolar environment stabilizes bacitracin A1 in a conformational structure with the lateral chain of apolar amino acids exposed on the external surface. This conformation of the macrocyclic dodecapeptide is ready to interact with Zn2+ ion, as pointed out by the strong increase of the association constant measured in water/2,2,2‐trifluoroethanol with respect to the value obtained in aqueous solution. In addition, whereas Zn2+ ion binding in aqueous solution provides a sensible reduction of peptide Stokes radius, no sensible variations following to ion binding were observed in hydro‐organic solution. The present results suggest that the apolar environment, rather than the metal ion binding, could be responsible for the conformational transition that brings bacitracin A1 towards its biologically active structure.*
Peak dispersion and contributions to plate height in nonaqueous capillary electrophoresis at high electric field strengths: Propanol as background electrolyte solvent
Authors: Palonen Sami , Porras Simo P. , Jussila Matti , Riekkola Marja‐Liisa 
Published: May 2003

AbstractPeak dispersion effects in nonaqueous capillary electrophoretic separations of aromatic anionic analytes were investigated in a propanolic background electrolyte solution. Poly(glycidylmethacrylate‐co‐N‐vinylpyrrolidone) coating was applied to the capillary to suppress the electroosmotic flow and to improve the repeatability of the migration times. Electrical field strengths up to 2000 Vcm−1 were applied in separations and the separation efficiencies were compared with theoretical values calculated on the basis of plate height theory. The contributions to the total plate height were calculated for injection plug length, diffusion, Joule heating, electromigration dispersion, analyte adsorption to the capillary wall, and detector slit aperture length. Analyte diffusion coefficients were measured by Taylor dispersion method, while distribution constants were measured chromatographically. Agreement between the calculated and empirical results was fairly good even though some approximations were required. In most cases the longitudinal diffusion contribution governed the total plate height, while the contribution of Joule heating was insignificant even at exceptionally high field strengths used. The relatively long detection slit aperture was found to influence the separation efficiency strongly, while the other dispersion sources that were investigated were of minor importance, except for adsorption in the case of one analyte. With all analytes, the dispersive effect of longitudinal diffusion was reduced as the field strength was increased, leading to enhanced migration velocities and faster separations.
Microemulsion electrokinetic chromatography for the analysis of green tea catechins: Effect of the cosurfactant on the separation selectivity
Authors: Pomponio Romeo , Gotti Roberto , Luppi Barbara , Cavrini Vanni 
Published: May 2003

AbstractMicroemulsion electrokinetic chromatography (MEEKC) was applied to the separation of six catechins and caffeine, the major constituents of the green tea. The developed methods involved the use of sodium dodecyl sulfate (SDS) as surfactant, n‐heptane as organic solvent and an alcohol as cosurfactant. The separations were performed under acidic conditions (pH 2.5 phosphate buffer, 50 mM) to ensure good stability of the catechins, with reversed polarity (anodic outlet). The effect of the alcohol nature on the MEEKC selectivity was evaluated; nine alcohols were used as cosurfactant: 1‐butanol, tert‐butanol, 1‐pentanol, 2‐pentanol, 3‐pentanol, cyclopentanol, 1‐hexanol, 2‐hexanol, and cyclohexanol. The migration order of (+)‐catechin (C), (−)‐epicatechin (EC), (−)‐epigallocatechin (EGC), (−)‐gallocatechin (GC), (−)‐epigallocatechin gallate (EGCG), (−)‐epicatechin gallate (ECG), caffeine and theophylline was significantly affected by the alcohol used as cosurfactant. Using nine microemulsions, four different selectivities were achieved: A (cyclohexanol); B (2‐pentanol, 3‐pentanol, 1‐hexanol, 2‐hexanol); C (1‐butanol, 1‐pentanol, cyclopentanol); D (tert‐butanol). MEEKC methods, based on 2‐hexanol and cyclohexanol as cosurfactant were validated and successfully applied to the analysis of catechins and caffeine in commercial green tea products.
Effect of diluting agent on sensitivity in capillary electrophoresis with amperometric detection
Authors: Wang Qingjiang , Ding Fei , Li Hui , He Pingang , Fang Yuzhi 
Published: May 2003

AbstractBesides the running buffer, pH of buffer, separation voltage and sampling time, the diluting agent was studied in this paper as one of the important factors influencing the sensitivity in capillary electrophoresis (CE) with amperometric detection (AD) when electrokinectic sampling was used. Clonidine hydrochloride, hydrochlorothiazide and rutin, which are positively charged, neutral and negatively charged, respectively, in aqueous solutions, could be perfectly separated by CE with 25 mmol·L−1 Na2B4O7 ‐ 50 mmol·L−1 NaH2PO4 as running buffer and detected by measuring their current responses with AD. Before CE running, some kinds of diluents including water, methanol, formamide, running buffer, hydrochloric acid and sodium hydroxide were, respectively, applied to dilute the stock solutions of above three analytes and their effects on the sensitivity of CE‐AD were investigated. The results showed that for electrokinetic injection, the current responses of these three analytes were greatly affected in different ways when different diluting agents were used. This method was applied to simultaneously determine the active ingredients in one Chinese compound hypotensor named Zhen Ju Jiang Ya Pian, in which the contents of clonidine hydrochloride, hydrochlorothiazide and rutin is very different as 0.03 mg : 5 mg : 20 mg per tablet, and satisfactory results were obtained by adjusting their sensitivity by selecting the suitable diluting agent.
Method development for the analysis of trans‐fatty acids in hydrogenated oils by capillary electrophoresis
Authors: de Oliveira Marcone A. L. , Solis Victor E. S. , Gioielli Luiz A. , Polakiewicz Bronislaw , Tavares Marina F. M. 
Published: May 2003

AbstractA novel capillary electrophoresis methodology using UV indirect detection (224 nm) for the analysis of trans‐fatty acids in hydrogenated oils was proposed. The electrolyte consisted of a pH 7 phosphate buffer at 15 mmol·L−1 concentration containing 4 mmol·L−1 sodium dodecylbenzenesulfonate, 10 mmol·L−1 polyoxyethylene 23 lauryl ether (Brij 35), 2% 1‐octanol and 45% acetonitrile. Under the optimized conditions, ten fatty acids, C12:0, C13:0 (internal standard), C14:0, C16:0, C18:0, C18:1c, C18:1t, C18:2cc, C18:2tt and C18:3ccc were baseline‐separated in less than 12 min. The proposed methodology was applied to monitor the formation of trans‐fatty acids during hydrogenation of Brazilnut oil. A crude oil sample (42.1% linoleic acid, 37.3% oleic acid, 13.4% palmitic acid, and 7.0% stearic acid) was mixed with 0.25% of a nickel‐based catalyst and submitted to two independent hydrogenation conditions: 175°C, 3 atm, 545 rpm for 60 min (GH1 sample), and 150°C, 1 atm, 545 rpm for 30 min (GH2 sample). For the most severe hydrogenation condition (higher temperature and pressure, under longer reactional period), a more complete conversion of linoleic and oleic acids into stearic acid occurred with concomitant formation of the trans‐species, elaidic acid (C18:1t). For the milder hydrogenation procedure that generated sample GH2, larger amounts of linoleic and oleic acids remained, in addition to the transformations already observed in the GH1 sample.
Electrophoretic analysis of quinone anion radicals in acetonitrile solutions using an on‐line radical generator
Authors: Esaka Yukihiro , Okumura Noriko , Uno Bunji , Goto Masashi 
Published: May 2003

AbstractWe have investigated analysis of anion radicals of phenanthrenequinone (PhQ) and anthraquinone (AQ) using acetonitrile‐capillary electrophoresis (CE) under anaerobic conditions. PhQ and AQ have relatively high negative reduction potentials meaning that their anion radicals are re‐oxidized quite readily by the surrounding O2 to disappear during analysis and we failed to detect them with our previous system. In this work, we have developed an on‐line system combining a unique electrolysis cell for generation of the radicals and a CE unit to keep the analysis system free from external O2 molecules and to reduce analysis time remarkably. As a result, electrophoretic detection of the anion radicals of PhQ and AQ has been achieved. Furthermore, we have observed hydrogen‐bonding interaction between the anion radicals and dimethylurea (DMU) using the present system and have indicated a characteristic interaction of the anion radical of PhQ as an ortho‐quinone with DMU.
Effects of organic solvents on sample pretreatment and separation performances in capillary electrophoresis
Authors: Huie Carmen W. 
Published: May 2003

AbstractA review of recent developments in theoretical as well as application studies concerning the use of organic solvents, either as purely nonaqueous solvents, hydro‐organic mixtures, or a combination of an organic solvent with another organic modifier(s), in the sample matrix and/or separation buffer for effecting sample pretreatment and/or improving separation performances in capillary electrophoresis (CE) is presented. In particular, recent advances made in furthering the basic understanding of selectivity changes that occur in capillary zone electrophoresis due the presence of organic solvents in the separation medium, based on in‐depth studies of fundamental processes, such as acid‐base chemistry, ion‐ion and ion‐solvent interactions, were discussed in detail. The utilization of organic solvents for improving the resolution of highly challenging and important separations, i.e., those involving the separation of positional and optical isomers, was also critically reviewed. Furthermore, a comprehensive survey of the use of organic solvents for on‐line sample pretreatment, e.g., minimizing aggregration and maximizing solubilization of hydrophobic analytes, improving concentration detection sensitivity for analytes via the use of sample stacking, was presented and discussed. Moreover, recent applications involving the use of organic solvents for improving the CE separations of a variety of molecular species with significance in various disciplines, including biological, environmental and pharmaceutical areas, were summarized and tabulated.
The role of organic solvents in the separation of nonionic compounds by capillary electrophoresis
Authors: Fritz James S. 
Published: May 2003

AbstractAlthough nonionic compounds can be separated by micellar electrokinetic chromatography (MEKC), application of this technique is restricted by a somewhat limited elution range. Incorporation of organic solvents in the background electrolyte (BGE) greatly extends the scope of MEKC and provides a major variable in optimizing the separation of neutral analytes. This paper provides a systematic review of the principles and scope of the separation of neutral analytes by capillary electrophoresis (CE) in organic‐aqueous solution. The methods surveyed include those that use tetraalkylammonium salts, dioctyl sulfosuccinate, lauryl poly(oxyethylene) sulfate. Polyaromatic hydrocarbon (PAH) compounds can be separated using sodium hexadecyl sulfate in 70% methanol (30% aqueous) to 100% methanol.
Dual stacking of unbuffered saline samples, transient isotachophoresis plus induced pH junction focusing
Authors: Shim Sang‐Hee , Riaz Asif , Choi Kihwan , Chung Doo Soo 
Published: May 2003

AbstractA dual stacking mechanism based on transient isotachophoresis (TITP) and induced pH junction focusing is demonstrated as a means to increase the concentration sensitivity in capillary electrophoresis of highly saline samples. When stacking was carried out with an unbuffered saline sample of fluorescein between two zones of low mobility background electrolyte at high pH under an electric field of reverse polarity, two transient peaks at both boundaries of the sample zone were observed. One peak at the rear boundary could be inferred as a transient isotachophoretic stacked zone. Through computer simulations of an unbuffered sample with a high concentration of sodium chloride, we showed that the fast moving zones of sodium and chloride ions induced pH changes at both boundaries to satisfy the electroneutrality condition and that the peak at the front boundary was due to the induced pH junction. To verify the pH changes, an indicator, thymol blue, was added to an NaCl solution and the color changes under an electric field were observed. The proposed mechanism was supported by observing the dual stacking procedure for an unbuffered sample of 4‐nitrophenol and measuring additional sensitivity enhancements by dual stacking for ten weakly acidic compounds. For the ten analytes including nucleoside phosphates, every dual stacking of an unbuffered sample exhibited an additional enhancement up to 86% larger than that of usual transient isotachophoresis of the corresponding buffered sample without loss of separation efficiency and reproducibility. Therefore, it would be useful to skip over buffering in sample preparation for TITP, contrary to the general recommendation.
Effects of background electrolyte composition and addition of selectors on separation selectivity in nonaqueous capillary electrophoresis
Authors: Fillet Marianne , Servais Anne‐Catherine , Crommen Jacques 
Published: May 2003

AbstractThis review gives a survey of the approaches employed to obtain, enhance and tune selectivity in nonaqueous capillary electrophoresis (NACE). Recent developments in NACE are described and the effects of background electrolyte composition and addition of selectors on separation selectivity are discussed. The use of one organic solvent, a mixture of several organic solvents or the use of additives to tune separation selectivity in NACE is presented and a list of relevant applications is included.
Comparison of different algorithms to calculate electrophoretic mobility of analytes as a function of binary solvent composition
Authors: Jouyban Abolghasem , Chan Hak‐Kim , Clark Brian John , Kenndler Ernst 
Published: May 2003

AbstractTen different mathematical models representing the electrophoretic mobility of analytes in capillary electrophoresis in mixed solvents of different composition have been compared using 32 experimental data sets. The solvents are binary mixtures of water‐methanol, water‐ethanol and methanol‐ethanol, respectively. Mean percentage deviation (MPD), overall MPD (OMPD) and individual percentage deviation (IPD) have been considered as comparison criteria. The results showed that a reorganized solution model, namely the combined nearly ideal binary solvent/Redlich‐Kister equation, is the most accurate model among other similar models concerning both correlation ability and prediction capability.
Salt dependence on vancomycin‐herbicide enantiomer binding: Capillary electrophoresis study and theoretical approach
Authors: André Claire , Guillaume Yves‐Claude 
Published: May 2003

AbstractIn a previous paper, a mathematical model was developed for the estimation of binding constants by capillary electrophoresis (Guillaume and Peyrin, Anal. Chem. 1999, 71, 2046–2052). This model was applied to determinate the binding constant of the guest‐vancomycin complex as well as the degree of complexation nc (percent of complexed guest). In this work, the guest molecule were a series of acid herbicide enantiomers (aryloxypropionic, aryloxyphenoxypropionic, and aminopropionic acid). The effects of the run buffer salt concentration on the herbicide‐vancomycin binding was clearly described by the determination of specific physicochemical parameters as well as thermodynamic data. These results demonstrate that a better understanding of the interactions involved in the guest molecule‐vancomycin binding allows to optimize the enantiomeric separation of this chiral guest molecule.