BUNSEKI KAGAKU Abstracts

A gold (Au)-deposited surface plasmon resonance (SPR)-based optical fiber sensor covered with an alkyl thiol spacer layer and a Teflon selective layer was developed. Small molecules in a sample solution selectively pass through the porous structure of Teflon AF1600, and are accumulated in the spacer layer. The response of the sensor increased by use of α-mercaptoethyl-ω-methoxy polyoxyethylene (PEG thiol). The sensor has no influences of glucose and tartaric acid in ethanol aqueous solutions. Ethanol concentrations in shochu, sake, and wine were measured directly and rapidly.

Capillary electrophoresis is a fast, cost-effective, and high-resolution separation technique. An advantage of ligand-exchange CE is that it is possible not only to change the chiral selector concentration, but also to mix the ligand and the central metal ion at any ratio. Chiral resolution by capillary electrophoresis was first achieved by ligand exchange, in which the Cu(II) complex with L-histidine was used as a chiral selector for the resolution of dansylated amino acids. In subsequent investigations, Cu(II) ion was generally used as the central ion. We tried to develop a novel ligand-exchange capillary electrophoresis by using a dual metal-ion system to simultaneously enantioseparate malic, tartaric and isocitric acids in juice samples, because the analysis of enantiomers and/or enantiomeric ratios in beverages can provide valuable information concerning food authenticity and adulteration. We also tried to develop another ligand-exchange capillary electrophoresis using borate anion as a central ion of the chiral selector to enantioseparate monosaccharides. In this paper, we introduce the above novel enantioseparation methods using ligand-exchange capillary electrophoresis.

Interfaces for Capillary electrophoresis-electrospray ionization mass spectrometry (CE-ESI-MS) and capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS) were self-designed and assembled for the speciation analysis of free aluminum and aluminum fluoride complexes. In CE-ESI-MS analysis, separated aluminum species were identified by their m/z values. Based on the results of CE-ESI-MS, aluminum species distributions were calculated by the results of CE-ICP-MS. A low detection limit (0.11 μM), which is suited to achieve the direct determination of aluminum species in natural water samples, was obtained by using Cool Plasma CE-ICP-MS. Experimentally determined aluminum species distributions showed good agreement with the calculated distributions. However, it was found that aluminum fluoride complexes were partly disintegrated during the separation process of CE. From a comparison of these results and other reports, new analytical methods that do not disturb the original species distributions were discussed.

In this study, a screw-capped sample stage was developed. By using the sample stage, a frozen hydrous sample was introduced to the analysis chamber without a glove box using a dry nitrogen purge. After having confirmed what was monitored, the temperature indicated that the sample had been cooled enough. The sample stage with a screw cap maintained the temperature of around −130℃ in the analysis chamber. As a test, we used an indium particle, which became attached to a silicon substrate, and then observed the surface, and confirmed that there was no adhesion of the ice onto the silicon substrate. In addition, a plant that absorbed cesium as a natural sample was analyzed, and imaging of the plant stem section was performed. As a result, the state of the absorbing water and cesium ions in the plant could be confirmed. Natural samples were conveyed to the analysis chamber quickly, and an analysis of the plant containing cesium ions was performed.

The availability of suitable standards (i.e., internationally calibrated reference materials) is a common issue as an analytical chemical precondition accurately measuring stable isotope ratios in many scientific disciplines. However, the traditional IAEA and NIST standards are in limited supply, particularly for the isotope analysis of organic hydrogen (D/H), carbon (¹³C/¹²C), nitrogen (¹⁵N/¹⁴N), oxygen (¹⁸O/¹⁶O), and sulfur (³⁴S/³²S). In a subproject coupled with the international project “Development of Organic H, C, and N Stable Isotope International Standards for NIST and IAEA”, we recently produced new reference materials of nine amino acids. These reference martials were designed as a working standard set to cover the naturally occurring nitrogen isotopic heterogeneity, ranging from −25 to +45 ‰ (δ¹⁵N value, vs. Air), which would be useful as the first internationally suitable reference materials for modern applications of the nitrogen isotope analysis of amino acids and other nitrogenous organic compounds.

Ion species contained in water samples accompanying produced oil and natural gas (deep subsurface water, subsurface brine, etc.) are generally measured by ion chromatography. However, abnormalities in the determination of low-concentration sulfate ion have been confirmed, and problems still remain unresolved. The high-salinity of those solutions is mentioned as being a cause. According to the literature, it was reported that abnormal quantitative values have occurred in samples containing high salinity. Therefore, we aimed to accurately measure the sulfate ion concentration of deep subsurface water and subsurface brine samples containing high salinity in this study. We made sure that in the sample-dilution experiments, the shift of the retention time and the decrease of the measured values had taken place due to the effects of the high-salinity of the solutions. We then performed cation-removal tests with H⁺-type cation exchange resin, and also with OnGuard II cartridge-Ag/H. It was confirmed that there were no problems in the recovery of anions from standard solutions and actual samples. We carried out cation-removal experiments without dilution, because the actual samples used in this study were low in sulfate-ion concentration. As a result, we were able to obtain sulfate ion concentrations higher by 140 – 491% than those without any pretreatment. Based on the pretreatment we proposed appropriately, we think, that it is possible to accurately determine the sulfate ion concentrations of deep subsurface water and subsurface brine samples.

Nitrogen atoms containing functional groups, such as amino group, were introduced by the electro-oxidation of carbon felt electrode into an ammonium carbamate aqueous solution. We found that the reduction wave of hypochlorite could be well-separated from that of oxygen in the cyclic voltammogram obtained by using this electro-oxidized carbon felt electrode as a working electrode. This result means that the selective reduction wave of hypochlorite appears due to an electrochemical introduction of electrocatalytic active sites containing nitogen atoms. This activated carbon felt electrode was applied for batch injection coulometric measurements of hypochlorite without any dissolved-oxygen interference. Reproducible current vs. time curves were obtained by repetitive measurements of hypochlorite; the relative standard deviation for ten successive measurements was 1.5%. A linear relationship was observed in the concentration range of up to 57 ppm (R² = 0.9997) with a detection limit of 0.18 ppm (S/N = 3). From these results, our proposed coulometric sensor is proven to be very promising for hypochlorite measurements without any dissolved-oxygen interference in practical applications.

A method to determinate the origin of the manufacturing of infant formula by using inductively coupled plasma mass spectrometry (ICP-MS) was developed. Fifty one Japanese and 19 Chinese samples were digested by a microwave digestion system. We decided to measure the Ba and Ce concentrations in infant formula in order to determinate the origin of the manufacturing because the origins of two elements involved the water of the manufacture. The concentrations of two elements showed obviously different tendencies between Japan and China. However, this method could not show any differences between Tokyo and Nagano in Japan. Deflection the kind of infant formula and the date of manufacture could also not be done. All samples were determinated based on a linear discriminant function to correct the origin. Because China is a large country, we need to establish a method to determinate the origin of the infant formula in various regions of China.

Standard bottom ash for elemental analysis of trace elements was developed and evaluated. Standard ash of municipal solid waste was prepared by sieving, pulverizing and homogenizing ash sample (bottom ash; Kyushu, Japan). The concentrations of Cr, Ni, Cu, Zn, Sr, Zr, Cd, Sn, Sb and Pb in the ash standard were given with alkali fusion/atomic absorption spectrometry (AAS) or inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis. The homogeneity of the ash powder was estimated by analysis of variance after Cochran test. The concentrations of 12 hazardous elements (Cl, Cr, Ni, Cu, Zn, Br, Sr, Zr, Cd, Sn, Sb, Pb) determined by X-ray fluorescence (XRF) analysis were used for analysis of variance, after validation of the quantitative results of these elements with reference materials (coal fly ash: NIST 1633b, fly ash: BCR-176R). For the determination of Cl and Br, X-ray tube power was used under 1.0 kW (50 kV – 20 mA) to prevent the volatilization with X-ray irradiation. There is no significant difference between the within-bottle variance and the between-bottle variance, indicating that the ash powder was sufficiently homogenous. The concentrations determined using XRF analysis were approximately the same as those resulting from AAS or ICP-AES analysis.

A standard-less X-ray fluorescence (XRF) analysis, “Fundamental Parameter Method (FP method)”, is widely used. The FP method gives concentrations of elements using the mathematically calculated XRF spectra based on fundamental parameters. These are not only fundamental physical constants such as the Plank constant but also incident X-ray spectrum, energy of characteristic X-rays and so on. We evaluated the availability of current FP method by conducting Aspirin and Euro coin analysis which is considered to be difficult and challenging. Concerning the evaluation process, we proposed a new improved XRD quantitative method using FP analysis results. The ratio of Lα : Lβ XRF lines is also a fundamental parameter. Pb Lα overlaps with As Kα. The overlapped peaks have typically been separated using the theoretical constant Lα : Lβ ratio. With the aim of future improvement of the FP method, we measured the Pb Lα : Lβ ratios by changing the measurement conditions, Pb concentration, coexistent elements, and so on, and observed large changes of the ratio. The change was quantitatively explained by the integral incident X-ray intensity from 60 keV down to each Pb absorption edge (L₁, L₂, L₃) energy, respectively. We confirmed the involvement of self-absorption, self-excitation, Coster-Kronig transition and Compton scattering. In the present study we proposed an intensity correction method to be used in converting the 2θ axis of the XRF spectra into energy. The intensity correction was typically neglected in the past XRF world.