Mitsuyoshi Okamoto

Breath acetone analysis with miniaturized sample preparation device: In-needle preconcentration and subsequent determination by gas chromatography–mass spectroscopy

A new approach to the determination of human breath acetone with particle-packed sample preparation needle was developed. The extraction needle was packed with a copolymer of methacrylic acid and ethylene glycol dimethacrylate as the extraction medium. For the analysis of breath sample, exhaled breath was collected in a sampling bag, and 50 mL of the breath sample was extracted with the needle-type sample preparation device followed by analysis using gas chromatography-mass spectrometry (GC-MS). After the optimization of several basic extraction conditions for standard acetone samples, breath acetone concentration taken from controlled type-2 diabetic patients was determined. Furthermore, time variations of breath and urine acetone of four healthy individuals under fasting conditions were measured. Urine sample was collected in glass vial, and urine acetone concentration was also determined with the extraction needle by analyzing the corresponding headspace gas. The results demonstrated that the particle-packed extraction needle showed an excellent extraction performance for acetone in both breath and urine headspace samples, and that there is a clear correlation between the concentration of breath acetone and HbA1c level of controlled type-2 diabetic patients. The breath acetone level in controlled diabetic patients was in the range between 0.19 and 0.66 ppmv, where its concentration in medically untreated type-2 patient was 0.92 and 1.20 ppmv. The breath acetone concentration in healthy male was increased to 5.66 ppmv under the 24 h of fasting test, and a high correlation between the breath and urine acetone concentration was also observed. On the basis of the above results, the potential applications of the proposed method to the diagnosis of diabetes and/or ketoacidosis were suggested.

Retention behaviour of large polycyclic aromatic hydrocarbons in reversed-phase liquid chromatography on a polymeric octadecylsilica stationary phase

Abstract Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and differential scanning calorimetry experiments were performed in order to study the retention mechanism in reversed-phase liquid chromatography for large polycyclic aromatic hydrocarbons. The effects of changing the mobile phase composition and column temperature were evaluated. The results suggest that a change in mobile phase composition from pure methanol to pure dichloromethane induces further non-planarity in non-planar solutes and also slightly changes the conformation of a polymeric octadecyl stationary phase. Conversely, a change to higher column temperatures drastically changes the structure of the stationary phase from solid-like to liquid-like, with only a small change of non-planar solutes to more non-planar conformations

Elution behaviour of peropyrene-type polycyclic aromatic hydrocarbons in various chemically bonded stationary phases in reversed-phase liquid chromatography

The elution behaviour of polycyclic aromatic hydrocarbons (PAHs, 13 of the 16 U.S. Environmental Protection Agency priority pollutants and peropyrene types) was studied on several chemically bonded stationary phases (octadecylsilicas, di- and triphenylsilicas, naphthylethylsilica and pyrenylethylsilica) under reversed-phase conditions. The results showed that the elution order of peropyrene-type PAHs is highly dependent on the degree of planarity of the solute and on the orderlines of the bonded phases, whereas no definite differences were found in the retention behaviour of the 13 small PAHs on various stationary phases. The characteristics of all the stationary phases could be classified by statistical cluster analysis.

Effect of column temperature on the retention of peropyrene-type polycyclic aromatic hydrocarbons on various chemically bonded stationary phases in reversed-phase liquid chromatography.

The effect of column temperature on the reversed-phase retention of polycyclic aromatic hydrocarbons has been investigated using various chemically bonded phases. Four solutes, coronene, tetrabenzo[a,cd,j,lm]perylene, tetrabenzo[a,cd,f,lm]perylene and benzo[lm]phenanthro[4,5,6-abcd]perylene, were used as the test probes. The temperature dependences of the retention are almost linear (the logarithm of capacity factor is proportional to the reciprocal of the column absolute temperature) with monomeric C18, monomeric C18 with endcapping and diphenyl bonded phases, while non-linear behaviour was observed with polymeric C18 phases. These differences in behaviour of the stationary phases are interpreted in terms of their structural differences.

Preparation and evaluation of N-(2-aminoethyl)-γ-aminopropyltrimethoxysilane-treated silica columns for the high-performance liquid chromatographic analysis of some aromatic amines

Abstract The retention and selectivity behaviour of some aromatic amines were studied by high-performance liquid chromatography using amino-chemically bonded stationary phases (column gel), prepared from silica gel treated with benzene solution containing 5–50% of N-(2-aminoethyl)-γ-aminopropyltrimethoxysilane (N2AAPTS). The N2AAPTS gel was compared with the 3-aminopropyltriethoxysilane (3APTS)-treated silica gel. From elemental analysis data for nitrogen and carbon, the maximum number of accessible amino surface groups per 100 A2 of silica gel (mean pore diameter 85 A, particle size distribution 5.8 μm) in N2AAPTS gel was estimated to be 1.81. The N2AAPTS gel provided better resolution of some amines than the 3APTS gel. The effect of the kind of component in the mobile phase on the capacity factor was studied using various alkanes (basic component) and normal alcohols (additive component).

Molecular-shape recognition of polycyclic aromatic hydrocarbons in reversed phase liquid chromatography

SummaryThe molecular-shape recognition of polycyclic aromatic hydrocarbons has been studied on various stationary phases in reversed-phase high-performance liquid chromatography. The examined stationary phases were phenyl-, diphenyl-, triphenyl- and benzyl-bonded silicas. The results of regression analysis inidcated that triphenylsilica is the best packing material to recognize the difference in the molecular-shape of structural isomers. This fact was confirmed by the separation of 4-ring isomers.

Behaviour of aromatic compounds in high-performance liquid chromatography on six kinds of silica gel modified with four types of phenyl groups

Abstract The retention and selectivity behaviour of some aromatic hydrocarbons, parabens (p-hydroxybenzoic acid esters) and nitrochlorobenzene compounds were studied by high-performance liquid chromatography on 24 kinds of phenyl-modified silica gels, prepared with xylene solution containing phenyldimethylchlorosilane (P), diphenylmethylchlorosilane (D), triphenylchlorosilane (T) or benzyldimethylchlorosilane (B), using six kinds of silica gel with various mean pore diameters and/or specific surface areas. From elemental analysis data for carbon, the maximum number of accessible phenyl surface groups per 100 A2 of silica gel (mean pore diameter 108 A, specific surface area 333 m2/g) in P, D, T and B gel was calculated to be 2.13, 1.90, 0.99 and 2.36, respectively. Using methanol—water mixtures as the eluent, aromatic hydrocarbons and parabens were separated on all the gels studied, but with different degrees of resolution. Nitrochlorobenzene compounds could not separated on the P, D and T gels, but were separated on B gel and also on an octadecylsilica column.

Evaluation of phenyldimethylethoxysilane treated high-performance thin-layer chromatographic plates. Application to analysis of flavonoids inScutellariae radix

SummaryThe retention and selectivity of flavonoids (baicalin, baicalein, wogonin, oroxylin A) inScutellariae radix have been studies by high-performance thin-layer chromatography on phenyldimethylethoxysilane-treated silica plates. The silica plates treated with phenyl groups were used for physical and chemical analysis. From elemental carbon analysis, the maximum number of bonded phenyl surface groups per gram was calculated to be 0.467×1021 (Oginal silica plate: Merck Art. 15109, Silica gel 100 F254). With methanol-1/15 M phosphate buffer (pH 6.2) mixtures as mobile phase, baicalin, baicalein, wogonin, and oroxylin A inScutellariae radix were separated. It has been shown that phenyl-treated plates are more suitable for selective separation of baicalin, baicalein, wogonin, and oroxylin A than octadecyl-treated plates.

Elution behaviour of peropyrene-type polycyclic aromatic hydrocarbons in liquid chromatography

The elution behaviour of peropyrene-type polycyclic aromatic hydrocarbons (PAHs) on variously bonded stationary phases in non-aqueous reversed-phase liquid chromatography has been investigated. The results clearly indicate that the retention behaviour is effected by the degree of planarity of the PAHs and by the properties of the stationary phases used. Solute planarity might also be influenced by solvation. Therefore, these factors combine to determine the retention of large PAHs.

Shape Selectivity of Polycyclic Aromatic Hydrocarbons and Fullerenes with Tri-Tert-Butylphenoxy Bonded Silica Phase in Microcolumn Liquid Chromatography

Abstract Retention behaviors of various planar and non-planar polycyclic aromatic hydrocarbons (PAHs), and all carbon compounds so-called fullerenes with 2,4,6-(tri-tert-butylphenoxy)dimethyl (TBP) silica phase and benzyldimethyl (Benzyl) silica phase have been investigated using microcolumn liquid chromatography system. The results clearly indicate that these phases possess a “non-planarity” recognition capability of PAHs. Non-planar solutes were retained longer than planar ones with these phases under certain separation conditions, although the opposite trend where the planar solutes are retained longer than the non-planar ones was observed with typical octadecylsilica (ODS) phases. This unique behavior can be explained by the specific molecular-molecular interaction between non-planar solutes and the stationary phase moiety having a cavity like structure made by the three tert-butyls and phenyl ring of the moiety. The separation of C60 and C70 were also examined and the difference of the structural uni...