Fumiko M. Yamamoto

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.

High-performance liquid chromatography-atmospheric pressure ionization mass spectrometry of gymnemic acids

Abstract Gymnemic acids (GAs), extracted from the leaves of Gymnema sylvestre, are a mixture of triterpene glucuronides possessing various physiological activities. The molecular masses of GA homologues were determined with high-performance liquid chromatography combined with atmospheric pressure ionization mass spectrometry. A mixture of GAs was chromatographed on an octadecyl silica column eluted with an aqueous methanol solution containing ammonium acetate, and directly introduced into an atmospheric pressure ionization mass spectrometer. Quasimolecular ions of GAs were detected as ammonium adduct ions and/or proton adduct ions. Molecular masses of thirteen different GAs and five compounds not containing glucuronic acid in their molecules were evaluated. Three pairs of geometrical isomers of GAs were found.

Ion chromatography of nitrite and carbonate in inorganic matrices on an octadecyl—poly(vinyl alcohol) gel column using acidic eluents

Low levels of carbonate and nitrite contained in inorganic matrices were determined by ion chromatography on an Asahipak ODP-50 poly(vinyl alcohol) gel-based reversed-phase column. With an acidic mobile phase, inorganic matrix anions and cations eluted near the void volume of the column, whereas carbonate and nitrite were retained and separated completely from the matrix ions. After the separation column, the peak response was enhanced using a cation-exchange hollow fibre and 25 mM sodium sulphate or alkaline enhancers. Sea-water samples can be applied directly for the determination of carbonate and added nitrite at ppm levels. The maximum sample volume that can be loaded on the column without peak deformation depended on the pH of the sample solution and the sulphuric acid concentration in the eluent. A 50 μl sea-water sample was applicable with a 2.5 mM acid eluent.

Prediction of thermodynamic retention behaviour in reversed-phase liquid chromatography with aqueous eluents and various concentrations of methanol by using the solubility concept model

Abstract The retention of a series of non-polar solutes in reversed-phase liquid chromatography was studied as a function of column temperature and mobile phase composition using methanol—water mixtures. The enthalpy change on transferring a solute from a stationary phase to a mobile phase was predicted from physicochemical parameters of the solute on elution with methanol—water between 40:60 and 100:0 by using the solubility concept model.

Chromatography of inorganic anions on poly(vinyl alcohol) gel columns with acidic eluents

SummaryPoly(vinyl alcohol) (PVA) gel shows ionic retention properties for common inorganic anions when an acidic eluent is used. The ionic property of the PVA gel is due to the proton-acceptable nitrogen atoms of the cross-linking agent and the carboxylic residues being comprised in the gel matrix. The extent of the net charge on the gel surface depends on the pH of the eluent. At a pH ranging from 2.3 to 5.3, the PVA gel behaves as a weak anion exchanger with very low ion-exchange capacity. At these conditions four UV-absorbing inorganic anions (bromate, bromide, nitrate, and nitrite) are separated by eluting with aqueous sulfuric acid. Alkyl groups introduced on the gel surface hinder the ionized solute molecules from accessing to the positively charged functional groups on the gel surface. A neutral solute (HNO2) is retained with non-ionic interactions.

Solubility parameter treatment for the characterization of the stationary phase in the reversed-phase chromatography of benzene derivatives

Abstract Non-polar benzene derivatives were chromatographed on seven commercially available octadecyl columns with aqueous methanol as eluent. To interpret the differences in the retention behaviour on these columns, the role of the stationary phase was investigated by means of the solubility concept model. An apparent solubility parameter of the stationary phase, δs′, was determined for the seven columns by using toluene as a standard solute. The values ranged from 14.32 to 14.91 (cal/cm3)1 − 2 with an 80% aqueous methanol eluent. The absolute value of the enthalphy change of solutes in the phase-transfer process. ΔH0, was larger on C18 columns with a smaller δs′. The ΔH0 value was predictable from the δs′ when the physico-chemical parameters of the solute and of the mobile phase were given. the δs′ was useful for characterizing the retention properties of the stationary phase.