Use of calixarene compounds as selectivity modifiers in capillary electrophoresis separations

Open tubular capillary electrochromatography of underivatized amino acids using Rh(III) tetrakis(phenoxyphenyl)porphyrinate as wall modifier

The separation of 17 "common" underivatized amino acids was attempted by open tubular capillary electrochromatography (OT-CEC) in fused-silica capillaries coated with Rh(III) tetrakis(phenoxyphenyl)porphyrinate (Rh(III)TPP(m-OPh)4OAc) using sodium phosphate and Tris-phosphate buffers as background electrolytes (BGEs). The OT-CEC separation of amino acids was compared with that obtained by capillary zone electrophoresis in bare fused-silica capillaries using the same BGEs. The amino acids were not derivatized and the UV-absorption detection was set at 200 nm. Depending on the experimental conditions at least 15 amino acids were separated. The best separations were obtained in a Rh(III)TPP(m-OPh)4OAc-coated capillary in 50 mM Tris-100 mM phosphate buffer at pH 2.25. Separation of the critical triplet Val-Ile-Leu was always at least indicated being better at higher BGE concentrations. Regarding the sensitivity of the method, lower concentration limits of detection (LODs) in the coated capillary were obtained for Thr, Gly, Tyr, and Val; the other amino acids exhibited lower LODs in the uncoated capillary. The separation of acidic amino acids was not achieved.

Influence of buffer zone concentrations on efficiency in partial filling micellar electrokinetic chromatography

The potential of counter pressure-moderated partial filling micellar electrokinetic chromatography (PF-MEKC) was investigated in this work. Plate numbers of homologous omega-phenylalcohols were measured in a two-plug PF-MEKC system varying the concentrations and hence the ionic strengths of the background buffer compared to the sodium dodecyl sulfate-containing separation buffer and the counter pressure on the cathodic buffer reservoir. It was observed that plate numbers are strongly influenced by both the buffer concentrations and the counter pressure. Highest plate numbers were obtained with a buffer system where the concentrations are adjusted such that the electroosmotic flow velocities in both zones are equal. Differences in the local electroosmotic flow velocities of the zones caused by different buffer concentrations are responsible for tremendously reduced plate numbers. The efficiency drop is explained in several models by the formation of an intersegmental pressure which produces a parabolically shaped laminar flow component in both zones. Thus, the electroosmotic plug-like flow profile is distorted and the efficiency is reduced. The effect of counter pressure on efficiency turned out to be very complex in dependence on the buffer system applied.

Study of a novel cationic calix[4]arene used a selectivity modifier in capillary electrophoresis with electrochemical detection

The use of a novel cationic calixarene, p-(quaternary ammonium) calix[4]arene, as selectivity modifier in capillary electrophoresis coupled with electrochemical detection was reported. The calixarene displayed good selectivity for the positional isomers of benzenediol and aminophenol and their successful separation was obtained under optimum conditions. The interaction mechanism between p-(quaternary ammonium) calix[4]arene and the solutes is discussed using the molecular modeling method. The detection limits by electrochemical detection for the most solutes studied here were below picogram level, which was approximately 2 orders of magnitude lower than those reported in the literature using UV detection. The results showed that electrochemical detection is especially suitable for an electrophoresis system where calixarenes are used as modifier.

Recent progress in capillary electrophoresis of metal ions

Advances in the fundamental studies and methodology of capillary electrophoresis (CE) as applied to metal ion analysis over the last two years are reviewed, with the objective of providing the interested reader with a state-of-the-art picture of technique's potentialities in the area. In particular, novel strategies for separation selectivity control and CE system innovations designed to enhance the detection sensitivity are described. In addition, a brief overview of the primary metal analytes and samples for which the technique appears to be best suited is given. The current limitations of the technique regarding most of all the implementation for routine use are considered along with the approaches on how they could be addressed. Finally, some pointers as to the likely trends in the future research are discussed.

Analysis of amines in plant materials

Biogenic amines are conveniently divided into aliphatic monoamines, aliphatic di- and polyamines and aromatic amines. These compounds are shown to fulfill an array of roles in cellular metabolism. Thus, amines are needed for growth and development and their metabolism appears to be coordinated with the cell cycle. Di- and polyamines, among which are putrescine, spermidine and spermine, are ubiquitous polycationic molecules that occur in all living cells. However, plants accumulate a number of specific related compounds under free or conjugated forms. In plant tissues, the molecular diversity combined with the fact that amine contents are highly responsive to developmental and environmental signals encouraged analysts to develop specific procedures for their isolation and characterization. The main goals were to develop high performance routine procedures in terms of selectivity, repeatability and detectability with minimum running costs. Domains of application concern not only fundamental aspects of amine biochemistry and physiology in plants but also increasing needs in the control of food and beverage quality from plant origin. The present review reports the most recent advances in extraction, identification and quantitation of amines in plant tissues with special interest in the analysis of original and uncommon metabolites. Emphasis is directed towards chromatographic and electrophoretic separation methodologies and new detection technologies of both derivatized and underivatized compounds including photometry, fluorometry, amperometry and mass spectrometry.

Recent advancements in amino acid analysis using capillary electrophoresis

Recent advances in the analysis of amino acids using capillary electrophoresis are addressed. This area of research continues to receive increased attention as is evident from the 62 references reviewed. This review discusses current detection strategies including UV absorbance, laser-induced fluorescence, electrochemical, and others. Separation methodologies for both derivatized and underivatized amino acids are reviewed. Both direct and indirect enantiomeric resolution of amino acids are addressed. Applications utilizing capillary electrophoresis for the analysis of amino acids are discussed. This review covers literature published in 1997 and 1998.