Souji Rokushika

Micro column ion chromatography with a hollow fibre suppressor

Abstract Two novel liquid chromatographic techniques, a hollow fibre suppressor and a micro column, have been coupled to give a micro column ion chromatograph. The column comprised a newly developed low-capacity anion-exchange resin for ion chromatography packed in a fused-silica capillary tubing (190 μm I.D.). The micro suppressor system was constructed from sulphonated hollow fibre tubing (10 × 0.2 mm I.D.). Excellent separations of inorganic anions and carboxylic acids were achieved with this system.

Gas chromatographic detection modes for the plasma chromatograph

Abstract The use of a plasma chromatograph as a gas chromatographic (GC) detector is described. It not only duplicates the capabilities of many known detectors, but also gives low-resolution qualitative detection of chosen compounds. Detection of GC effluents comparable to the flame ionisation and electron capture detectors is demonstrated using positive and negative modes of operation of a research-oriented instrument. A tunable mobility detection of both positive and negative ions selected in the mobility spectra of given compounds provides highly sensitive, and low-resolution qualitative detection of GC effluents. The use of this technique is facilitated by the availability of a number of reference spectra of different classes of compounds previously reported. Further development of the plasma chromatographic instrumentation for multi-mode detection of GC effluents is suggested.

Retention properties of the fluorinated bonded phase on liquid chromatography of aromatic hydrocarbons.

The unique characteristics of a bonded-fluoroalkylsilane column, Fluofix, are described by comparison with those of a bonded octylsilane column, C8, in the reversed-phase chromatography of aromatic hydrocarbons. The selectivity of homologous aromatics on the fluorinated column varied with the methanol concentration in the eluent. At a larger proportion of methanol than 80:20 (v/v) the larger aromatics eluted faster than the smaller ones. However, with less methanol, the aromatics were eluted in order of their molecular size, as usually reported for a conventional hydrocarbonaceous column. A dependence of the retention mechanism on the composition of the eluent was suggested by the decrease in the entropy-enthalpy compensation temperature, beta, with increase of methanol concentration in the eluent. In order to explain the concentration dependence of the retention, the molecular interaction energy in the retention process was calculated by computer simulation. The interaction energy between aromatics and the stationary ligand on the Fluofix column was smaller than that on the C8 column and comparable to the interaction energy between the aromatics and methanol. At higher methanol concentrations, solute-fluorinated ligand complex formation was obstructed by the methanol molecules solvating the solute, reducing the retention of the larger aromatics.

Microbore packed-column anion chromatography using a UV detector

Abstract A micro packed-column anion chromatograph with a UV detector has been constructed and the applicability of the system is demonstrated. A flexible fusedsilica capillary (0.19 mm I.D.) was used as a chromatographic tube and a surface-agglomerated and bonded low ion-exchange capacity anion-exchange resin, developed for ion chromatography, was packed into an ion-exchange column. Separations of inorganic ions, nucleobases, nucleotides and organic-acids were achieved using this system.

A Fundamental Study on Aqueous Solutions of 2-Methyl-2-Nitrosopropane as a Spin Trap

Several aspects of spin trapping with 2-methyl-2-nitrosopropane (MNP) were studied. Compounds produced from dimer MNP in aqueous solutions prepared for spin trapping were analyzed as t-butylnitrosohydroxylamine, t-butyl alcohol, and isobutene. The procedure for obtaining solutions containing the lowest concentrations of these products and the highest of monomer MNP with spin-trapping ability was established. The ESR signals of di-t-butyl-nitroxide in the light-irradiated aqueous MNP solution increased when the pH of the solution was raised. It was found that nitrous acid generated in the irradiated solution reacts with di-t-butylnitroxide and an unidentified compound, giving rise to a stable, positively charged diamagnetic intermediate. The production of the nitroxide from the intermediate caused by raising the pH might be relevant to the increase in ESR signals.

Anion chromatography of carboxylic acids and keto acids using a hollow-fibre suppressor

Abstract Anion-exchange chromatography of carboxylic acids and keto acids was carried out on an ion chromatograph equipped with a hollow-fibre ion-exchange membrane suppressor and a dual detector system comprised of a UV and a conductivity detector. Low-molecular-weight monocarboxylic acids were separated with a sodium tetraborate solution as eluent, and dicarboxylic acids and corresponding keto acids with a carbonate butter as eluent. The sensitivity of the conductivity detector to carboxylic acids was a function of the pK values of the acids. The detection limit for succinic acid was less than 0.5 nmol.

Elution behaviour of aliphatic carboxylic acids on a strong cation-exchange resin column

Abstract The retention behaviour of aliphatic mono- and dicarboxylic acids on a strong cation-exchange resin column in the alkali metal and ammonium ion forms has been studied by ion chromatography. Carboxylic acids eluted in order of the carbon number. Small acids, such as formic, oxalic and malonic acids, were excluded from the column by the ionic exclusion effect, whereas the larger carboxylic acids were strongly retained owing to hydrophobic interactions. The retention of carboxylic acids was controlled through the combination of several interaction forces such as Donnan potential, size exclusion and hydrophobic interactions. The elution volumes of carboxylic acids on resins in various ionic forms decreased in the order K+ > Cs+ > NH+ > Na+ > Li+ > H+ resin forms.

Subsite structure of the β-glucosidase from Aspergillus niger, evaluated by steady-state kinetics with cello-oligosaccharides as substrates☆

The beta-glucosidase from a commercially available preparation from Aspergillus niger was highly purified. The Michaelis constant Km and the molar activity K0 for cello-oligosaccharide substrates Gn (n = 2-6) were obtained by steady-state kinetic analysis on the beta-glucosidase-catalyzed hydrolysis at 25 degrees C and pH 5.0. Stoichiometric production of Gn-1 by the beta-glucosidase reaction for Gn was confirmed by HPLC techniques. Based on Km and K0 for Gn, subsite affinities (Ai, i = 1-6) were estimated as follows (kcal/mol): A1 = 1.3, A2 = 5.2, A3 = 0.65, A4 = -0.10, A5 = -0.65, and A6 = -0.26, of which A1-A3 are much higher than those of the beta-glucosidase of Candida wickerhamii. The subsite structure is quite similar to that of the alpha-glucosidase of A. niger, whereas the dependence of k0 on n is highly characteristic for beta-glucosidase, and decreases with n, suggesting some interaction between the particular subsites.

Studies of spin-trapped radicals in gamma-irradiated aqueous solutions of thymidine-5'-monophosphate and cytidine-5'-monophosphate by liquid chromatography and ESR spectroscopy.

Aqueous solutions of thymidine-5′-monophosphate and cytidine-5′-monophosphate were γ-irradiated with 2-methyl-2-nitrosopropane as a spin-trapping reagent. Liquid chromatography was applied to separate the stable spin-trapped radicals in the irradiated solutions. The eluate was passed through flow cells of ESR and uv detectors and collected by a fraction collector. The amount of residual sugar in the each fraction was determined by the

Polyacrylate liquid crystalline stationary phases in supercritical fluid chromatography with carbon dioxide mobile phase

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