Katsumi Uchiyama

Simultaneous separation of sixteen positional and optical isomers of the tryptophan family by ligand-exchange micellar electrokinetic chromatography

SummaryLigand-exchange micellar electrokinetic chromatography has been used for the simultaneous separation of 16 positional and optical isomers of the tryptophan family. The Cu(II) complex with L-hydroxyproline was used as the chiral selector. Two groups of anionic surfactant, linear alkylbenzenesulfonates (LAS) and straight-chain alkyl sulfates such as sodiumn-decyl sulfate (SDeS), sodium dodecyl sulfate (SDS) and sodiumn-tetradecyl sulfate (STS), were used for simultaneous separation. The best result was obtained by use of SDS. The influence of SDS concentration and of pH on the separation was investigated. The separation behavior in the absence of the Cu(II) complex with L-hydroxyproline was also examined. Use of organic modifiers causes the resolution to decrease. Relationships between the logarithm of the octanol-water partition coefficient (logPOW) and resolution, and between logPOW and migration time are discussed.

Determination of critical micelle concentrations of anionic surfactants based on ligand exchange micellar electrokinetic chromatography

Abstract A new method for determining the critical micelle concentration (CMC) of anionic surfactants by ligand exchange-micellar electrokinetic chromatography (LE-MEKC) has been developed. In the separation of amino acid enantiomers by LE-MEKC using a copper complex with l -hydroxyproline as a chiral selector, it has been noted that the addition of anionic surfactants to the electrolyte causes the reversal of the enantiomer migration order EMO. The point of reversal is correlated with the CMC. Resolution (Rs) decreases with the addition of surfactant below the CMC and increases above the CMC. The inflection point at which Rs equals zero was used for the calculation of the CMC. Based on this fact, the CMCs of anionic surfactants sodium n -decyl sulphate, sodium dodecyl sulfate and sodium n -tetradecyl sulphate in 25xa0mM CuSO 4 , 50xa0mM l -hydroxyproline at pH 4 have been determined. The CMCs in the presence of 2.5% acetonitrile were also determined. Results show that the CMCs of anionic surfactants increased with the addition of acetonitrile.

Separation behavior of amino acid enantiomers in ligand exchange micellar electrokinetic chromatography

The separation of amino acid enantiomers using a Cu(II) complex with l-hydroxyproline as a chiral selector has been investigated by ligand exchange micellar electrokinetic chromatography. It was found that anionic surfactants like sodium dodecyl sulfate (SDS), sodium n-decyl sulfate, and sodium n-tetradecyl sulfate can not only improve the resolution of d,l-enantiomers, but also can change their migration orders. The migration order of o-, m-, and p-positional isomers of fluorophenylalanine and tyrosine was reversed when the concentration of SDS exceeded a certain concentration. Tween 20 improved the separation efficiency, but the migration time became longer. Cetyltrimethylammonium bromide can change the direction of electroosmotic flow, but it has no significant improvement on resolution. Organic modifiers cause the decline of resolution, but not the reversal of enantiomer migration order (EMO). A possible mechanism of the reversal of EMO is presented.xa0©1999 John Wiley & Sons, Inc.xa0J Micro Sep 11: 534–540, 1999

Comparison of three different anionic surfactants for the separation of hydrophobic compounds by nonaqueous capillary electrophoresis

The effect of the three different surfactants, sodium dodecyl sulfate (SDS), diethylhexyl sodium sulfosuccinate (AOT), and taurodexycholic acid sodium salt (STDC) on the nonaqueous capillary electrophoretic separations of hydrophobic compounds were compared with formamide containing 20 mM K2HPO4 as electrolyte solvent. Separations of all selected uncharged hydrophobic compounds, e.g., p‐arylacetophones were shown to be strongly dependent on the kind of surfactant. The electrolyte containing 180 mM SDS provided the best result for the selected samples.

A flow-based enzyme-linked immunosorbent assay on a polydimethylsiloxane microchip for the rapid determination of immunoglobulin A.

A flow-based enzyme-linked immunosorbent assay (ELISA) on a polydimethylsiloxane (PDMS) microchip has been developed for the rapid determination of immunoglobulin A (IgA). The analytical principle of this integrated method is the same as the conventional sandwich-type ELISA. A primary antibody (anti-IgA) was adsorbed on the surface of a PDMS microchannel, and then an antigen (IgA) and a secondary antibody (anti-IgA HRP labeled) were reacted successively. The resulting antigen-antibody complex, fixed on the surface of the microchannel, was detected using Amplex((R)) Red and a fluorescent imaging system. The calibration curve of the IgA standard solution was linear in the range of 0-50ng/mL at the flow rate of 10muL/min. This flow rate corresponds to the reaction time of 4.8s. Compared to the conventional assay on a 96-well microtiter plate, the present assay on the microchip dramatically shortened the reaction time necessary for the enzyme-substrate reaction from 30min to 4.8s, i.e., to 1/375. The amounts of the reagent and sample were also reduced to 1/100 compared to the 96-well microtiter plate.

Enantioseparations of dansyl amino acids by capillary electrophoresis using Cu(II) complexes with L-amino acylamides as chiral selectors in electrolytes

Enantioseparations of dansyl amino acids using Cu(II) complexes with L-amino acylamides as the chiral selectors in the electrolyte solution were investigated by capillary electrophoresis. It has been demonstrated that the Cu(II) complexes with L-amino acylamides such as L-phenylalaninamide, L-prolinamide, and L-alaninamide are suitable for use as chiral selectors for enantioseparations of dansyl amino acids. The optimal separation conditions were examined. The employed chiral ligands exhibited different enantioselectivities and enantiomer migration orders. The enantiomer migration orders are discussed by using three different chiral selectors. L-enantiomers migrate faster than D-enantiomers when Cu(II)-L-phenylalaninamide and Cu(II)-L-alaninamide are used as chiral selectors, but D-enantiomers faster than their (--counterparts in the Cu(II)-L-prolinamide system.

Monitoring nano-flow rate of water by atomic emission detection using helium radio-frequency plasma

Recently, high-performance nano-scale flow pumping systems have been developed for micro and miniaturized analysis systems. A novel device capable of measuring and monitoring nanoliter scale flow rates has been required for the further development of the pumping system. In this study, an atomic emission detector using helium radio-frequency plasma (RFP-AED) was used for the measurement of the nanoliter scale flow rate of water by quantitatively detecting the emission from hydrogen in the water molecules. Monitoring nano-flow rates of water in the range up to 1.0 microl min(-1), and the change in the flow rate by the indication of the ratio of the emissions of H (656.3 nm) and He (667.8 nm) were successful. At present, the lowest flow rate that could be determined reproducibly was 4 nl min(-1) calculated as five times the standard deviation of the background noise. Additionally, similar evaluations for the deviation of each flow rate by using the RFP-AED and a flow-injection system were produced.

Enantioseparation Of Aromatic Dipeptides Using Carboxymethyl-β-Cyclodextrin Polymer As Chiral Selector By Capillary Electrophoresis

ABSTRACT Chiral separation of peptides is of interest because of the different biological activity of enantiomers. In this report, several underivatized dipeptides with benzene moieties were optically resolved by employing carboxymethyl-β-cyclodextrin polymer(CM-β-CD polymer) as chiral selector. The effects of different cyclodextrin types, selector concentration, buffer pH, and organic additive were examined. Selector concentration and buffer pH played significant roles in resolution. Enantioseparation was found to be negatively influenced by adding the organic additive into running buffer and even completely lost at the organic additive content of 16%. It was also noted that the dipeptides with short chain in the vicinity of the second chiral carbon atom showed better chiral resolution by using CM-β-CD polymer than by using either carboxyethyl-β-CD or succinylated-β-CD. Simultaneous chiral separation of a mixture of DL-Ala-DL-Phe and DL-Leu-DL-Phe was also obtained using 27 mg/ml CM-β-CD polymer in the running buffer at pH5.12.

Thermodynamic approaches to intermolecular interaction and retention behavior in liquid chromatography

Abstract In this work, we investigated the intermolecular interaction between the stationary phases and solutes and retention behavior in liquid chromatography by thermodynamic analysis. The intermolecular interactions between four stationary phases chemically bonded with octadecyl (ODS), phenyl (Ph), pyrenyl (PYE), and β‐cyclodextin bromide (β‐CD), and 53 solutes including 27 compounds of p‐substituted alkylbenzenes (PSABs), 14 compounds of polyaromatic hydrocarbons (PAHs), and 26 compounds of substituted benzenes were examined by using both methanol–water and acetonitrile–water as mobile phases. It has been observed that there are obvious differences in π–π intermolecular interactions among the stationary phases of ODS, Ph, and PYE by plotting ln k′ with enthalpies (ΔH). Based on the thermodynamic analysis on the interaction between β‐CD column and solutes, it was known that the solutes having similar molecular lengths with β‐CD resulted in large enthalpy changes in the host–guest interaction. Besides, both hydrophobic and host–guest interactions make contributions to the retention of solutes on the β‐CD stationary phase; and the structures of solutes have critical influence on the retention. Further, from the thermodynamic point of view, the retention mechanisms such as partitioning or adsorption in liquid chromatography have been discussed.

Separation selectivity in micellar electrokinetic chromatography using different anionic surfactants as pseudo-stationary phases

SummaryMicellar electrokinetic chromatography (MEKC) and ligand exchange-MEKC have been widely used for the separation of achiral and chiral compounds. For the separation of different compounds, one expects to obtain the desired different separation selectivity by choosing different surfactants as pseudo-stationary phases. This paper describes a comparative study on the separation selectivity in MEKC and LE-MEKC using different anionic surfactants such as sodium dodecyl sulfate (SDS), sodium alkyl polyoxyethylene sulfate (AES-Na) and sodium α-sulfonated fatty acid methyl esters (α-SF-Na). Different selectivities were observed with these anionic surfactants. For the separation of aromatic derivatives by MEKC, better selectivity was obtained by using AES-Na than SDS micellar phases. For the simultaneous separation, of positional enantiomers ofo-, m- andp-fluoro-DL-phenylalanine by LE-MEKC, the SDS micellar phase provided the best selectivity among these anionic surfactants. Furthermore, the critical micelle concentrations (CMC) of these surfactants were also estimated by LE-MEKC.