Hiroto Ozaki

Electrokinetic chromatography with 2-O-carboxymethyl-β-cyclodextrin as a moving “stationary” phase

Abstract Preliminary results are presented on a new type of liquid chromatography, based on inclusion complex formation in a solution of a β-cyclodextrin derivative having an ionized group, 2-O-carboxymethyl-β-cyclodextrin (β-CMCD), combined with electrokinetic migrations. Only the host—guest interaction between β-CMCD and the solute operates as the distribution process, and electroosmosis and electrophoresis in an open-tubular capillary filled with a β-CMCD solution permit differential migrations between the host and guest molecules. Separations of some aromatic isomers are shown, and retention parameters and the distribution coefficient are discussed.

Micellar electrokinetic chromatography—mass spectrometry using a high-molecular-mass surfactant on-line coupling with an electrospray ionization interface

On-line coupling between micellar electrokinetic chromatography (MEKC) and mass spectrometry (MS) was studied with a high-molecular-mass surfactant and an electrospray ionization interface (ESI). A high-molecular-mass surfactant, butyl acrylate-butyl methacrylate-methacrylic acid copolymer sodium salt (BBMA), was employed as a pseudo-stationary phase for an on-line MEKC-MS system. BBMA and a minor component separated by size-exclusion chromatography were determined by ESI-MS. No major ion from the BBMA polymer was detected. The BBMA micelle functioned successfully as the pseudo-stationary phase in a 10 mM ammonium formate buffer containing 10% methanol. Five standard compounds, phenyltrimethylammonium chloride, 1-naphthylamine, quinine sulfate, tetraphenylphosphonium chloride and octaoxyethylenedodecanol, were separated by MEKC and detected by MS. The effects of the concentrations of BBMA on the separation and sensitivity in MEKC-MS were studied. MEKC-MS with BBMA was applied to the separation and detection of a standard mixture of sulfamides.

Micellar electrokinetic chromatography using high-molecular surfactants use of butyl acrylate-butyl methacrylate-methacrylic acid copolymers sodium salts as pseudo-stationary phases

Abstract Butyl acrylate-butyl methacrylate-methacrylic acid copolymers sodium salts (BBMA), high-molecular surfactants ( M r ≈ 40 000), were utilized in micellar electrokinetic chromatography. Non-ionic test solutes were successfully separated with a 2% BBMA solution in a borate-phosphate buffer (pH 8.0). BBMA showed significantly different selectivity for naphthalene derivatives in comparison with sodium dodecyl sulfate. The capacity factors were proportional to the concentration of BBMA, and the critical micelle concentration was found to be substantially close to zero, suggesting that one BBMA molecule forms one micelle. Effects of the pH, the composition and the molecular mass of BBMA were studied.

Separation and detection of closely related peptides by micellar electrokinetic chromatography coupled with electrospray ionization mass spectrometry using the partial filling technique

Closely related peptides such as neurotensin and angiotensin analogues were separated by capillary zone electrophoresis using a nonionic surfactant, sucrose monododecanoate, as a micelle forming reagent. These peptides were detected by an on-line coupled mass spectrometer using an electrospray ionization interface. However, the presence of the micelles in the separation solution drastically reduced the sensitivity of the mass spectrometer. Therefore, a partial filling technique was employed to prevent the micelles from entering the mass spectrometric interface. A part of the capillary from the injection end was filled with the micellar solution in this technique. Analytes passed through the micellar zone during the electrophoresis and when the separated analytes reached the detection end of the capillary, the micellar zone was still behind the analyte zones, because the nonionic surfactant moved very slowly in acidic conditions. Thus the technique was very useful for mass spectrometric detection for CE when the micellar solution was employed for separation. The optimization of separation and detection conditions was investigated.

Micellar electrokinetic chromatography using high-molecular-mass surfactants: comparison between anionic and cationic surfactants and effects of modifiers

Abstract Two high-molecular-mass surfactants, butyl acrylate-butyl methacrylate-methacrylic acid copolymer sodium salt (BBMA) and butyl methacrylate-methacryloyloxyethyltrimethylammonium chloride copolymer (BMAC), were utilized as new pseudo-stationary phases in micellar electrokinetic chromatography (MEKC). As with BBMA, BMAC was successfully employed as a pseudo-stationary phase, but reversal of the electroosmotic flow was observed. The capacity factors were proportional to the concentration of BMAC, and the critical micelle concentration was effectively zero. The effect of the addition of methanol and a non-ionic surfactant were studied in MEKC with BBMA. Chiral separation was studied by cyclodextrin (CD) modified MEKC with BBMA: enantiomeers of dansylated- dl -amino acids were separated with 2% BBMA and 10 mM β-CD, giving larger separation factors than those obtained with 100 mM sodium dodecyl sulfate adn 60 mM β-CD.

On-line micellar electrokinetic chromatography–mass spectrometry with a high-molecular-mass surfactant

Abstract On-line coupling of micellar electrokinetic chromatography and electrospray ionization mass spectrometry (MEKC–ESI-MS) using a high-molecular-mass surfactant was explored. Some standard mixtures, pharmaceuticals and industrial surfactants were separated and detected with 1% butyl acrylate–butyl methacrylate–methacrylic acid copolymer sodium salt (BBMA) in 20 mM ammonium formate (pH 7). The effect of the concentration of surfactants on sensitivity was studied with direct injection of caffeine to the ESI-MS. The partial filling technique in MEKC was studied with BBMA. Before the pseudo-stationary phase zone reached the detector, six non-ionic naphthalene derivatives were separated successfully by partial filling MEKC with a 5% BBMA zone introduced at 50 mbar for 20 s. The partial filling method was also applied to the on-line MS detection of caffeine and its metabolites.

Theoretical Analysis of Critical Flowable Physical Gel Cross-Linked by Metal Ions and Polyacrylamide-Derivative Associating Polymers Containing Imidazole Groups

When the polymer chains are cross-linked by physical bonds having a finite lifetime, the relaxation time and viscosity do not diverge at the gel point though percolation occurs. These undivergent quantities are related to the finite-sized “largest relaxed cluster,” which can relax before it breaks. Its size is the key rheological parameter characterizing of the critical physical gels. In order to evaluate this characteristic size, we propose here a generalized phenomenological model for the viscoelasticity of critical physical gels. We apply the theory to the previously reported experimental result for the physical gel consisting of polyacrylamide-derivative associating polymers containing imidazole groups cross-linked by coordination bonds with Ni ions. We successfully estimate the size of the largest relaxed cluster and the fractal dimension. The size is in good agreement with that estimated from the mean-square displacement of probe particles at the gel point by microrheological measurement. We also compare this system with the poly(vinyl alcohol) hydrogel cross-linked by borate ions, and show that the difference in the cluster structures is originating from the differences of precursor chain properties such as overlap concentration and radius of gyration and of the cross-linking states in these systems.

Theoretical Study of Network Formation and Mechanical Properties of Physical Gels with a Well-Defined Junction Structure.

A statistical-mechanical theory of thermoreversible gelation considering loops for the system consisting of bifunctional polymer units carrying A functional groups and trifunctional units carrying B functional groups at their ends is constructed. We obtain the sol-gel transition line and the properties of the post-gel region as functions of the polymer concentration, temperature, association constant, and loop parameter using the present theory. In this article, we calculate the number concentration of elastically effective chains in the gel region and obtain the shear modulus by an application of the phantom network theory. The shear modulus obtained by this theory is lower than that obtained by conventional theory because of loop formation. We find that these theoretical results are in good agreement with the experimental data.