BUNSEKI KAGAKU Abstracts

Thermochemolysis-gas chromatography (thermochemolysis-GC) in the presence of organic alkali was applied to a structural analysis of oil components in Japanese traditional carpet “yuton”, consisting mainly of Japan paper and perilla oil. At first, yuton samples after 5 and 45 years of manufacture by craftsmen were subjected to thermochemolsys-GC in the presence of tetramethylammonium hydroxide (TMAH) at 400°C. The resulting chromatograms of both yuton samples commonly showed two characteristic peaks of dimethyl esters of dicarboxylic acids, such as suberic and azelaic acids, which had been reported to be the typical thermochemolysis products from oxidized drying oils. Particularly, in the chromatogram of the older yuton sample, the fatty acid components derived from the original perilla oil were almost missing, while the dicarboxylic acid components were observed as slightly weaker peaks than those in the case of the newer one. This observation suggests that the refractory network structures were formed through promoted oxidation of perilla oil components in the older yuton. Furthermore, it was revealed that these dicarboxylic acid components originated from the network structures based on thermochemolysis-GC measurements of perilla oil samples cured by heating for 5 hours at 100°C. These results suggest that the network structures of oxidized oil components are formed on the surface of actual yuton increasingly over prolonged periods of time, which in turn give rise to the unique property that its strength and repellency become the highest after 20–30 years of use.

A new analytical technique to characterize the physical and chemical properties of materials in the “over thousand degree centigrade” (OTD) region, a complex impedance spectroscopy using flames (OTD-CIS) was proposed. Since the flames have electric conductivity, they can be used as an electric probe instead of conventional metal electrodes that are interactive with samples in the OTD region. Intrinsic electric properties of the flame, rectification in DC characteristics and a response of positive ions in AC characteristics required specific experimental and analytical techniques to obtain OTD-CIS spectra, i.e., frequency response measurement using a pulsating voltage and a differential analysis to eliminate the background response of the flame. By using these techniques, OTD-CIS was successfully demonstrated for an aluminum oxide (Al₂O₃). Although the dielectric constant of Al₂O₃ in the OTD region was not changed from that at room temperature, the resistivity was continuously reduced in the OTD region.

We have developed molecular tips of scanning tunneling microscopy (STM) for single-molecule analyses on solid surfaces. The molecular tips enable the selective observation of functional groups and metal ions on the basis of chemical interactions between the sample and tip molecules. A deliberate design for the chemical structure of a molecular tip leads to sophisticated molecular recognition at the single-molecule level, including chiral recognition and selective visualization of atomic defects in carbon nanotubes. Moreover, electron transfer from a single molecule to adjacent another single molecule can be quantified by molecular STM tips. Such electron transfer plays an essential role in the functional nanostructures realized by a self-assembly technique, in which chemical interactions are utilized to organize molecules. However, rather little is known about the electron-transfer property between single molecules. In addition, we have demonstrated that the measurement of this electron transfer is useful for ultrasensitive sensing applications, e.g., the detection of a single DNA molecule.

A simple determination method was developed to measure ¹²⁹I in low-level radioactive liquid waste solidified with bitumen. A simulated bituminized product sample was cut into 0.02 g pieces ; subsequently, these pieces and sodium carbonate were heated in an electric furnace. This procedure could well decompose the bituminized sample without volatilizing ¹²⁹I. Sixty to seventy-five percent of ¹²⁹I was recovered by a solid-phase extraction disk from a solution containing the decomposed sample. A dynamic reaction cell inductively coupled plasma mass spectrometer was applied to measure ¹²⁹I ; as a result, detection limit of ¹²⁹I was reduced by a factor of about 6 compared with the conventional ICP-MS measurement. The determined radioactivity concentration for the simulated bituminized sample containing ¹²⁹I was in good agreement with the expected value within a 6% error.

The acidity of magnesium salts-silica gel composites was measured by absorption spectrophotometry in the micro-region using a confocal laser scanning microscope (CLSM). It has been reported that MgCl₂-SiO₂ releases protons under dry conditions, and goes back to neutral under wet conditions. At first, using five kinds of tetraarylporphyrins, the absorbance (A_P) at 515 nm due to a free base type and that (A_G) at 650 nm due to the protonated porphyrins were measured in a CHCl₃-MeOH-water solution, whose apparent pH was adjusted by HClO₄. Fraction (F-value) of A_P [F = A_P/(A_G + A_P)] was calculated at every apparent pH to produce apparent pH-profiles of the F-values for all porphyrins. The profiles were fitted by sigmoid curves. Second, the porphyrin was adsorbed on MgCl₂-SiO₂. The porphyrin-adsorbed composite was kept under the given relative humidity conditions for 3 days and subjected to CLSM analysis. The F-values of the porphyrins adsorbed on the composites were obtained from the absorption spectra to determine the apparent pH using fitting curves. As a result, the MgCl₂-SiO₂ had an apparent pH of 1.73 under dry conditions, and 4.39 under wet conditions. Moreover, the pH values of the Mg(NO₃)₂-SiO₂ composite and the MgSO₄-SiO₂ composite were measured.

The concentrations of methylmercury (MeHg) and ethylmercury (EtHg) were determined in fish and shellfish. Both MeHg and EtHg were isolated by acid leaching (KBr-H₂SO₄-CuSO₄); MeHg and EtHg bromides were extracted into an organic solvent [cyclohexane/ethyl acetate (1 : 1)], then reextracted into 1% cysteine-sodium acetate. MeHg and EtHg bromides were derivatized with sodium tetraphenylborate (NaBPh₄), and extracted with hexane. The organic phase containing methylphenylmercury and ethylphenylmercury was injected into GC/MS (SIM). As a result, even if we did not use benzene or toluene for the extracting solvent, it became possible to extract MeHg and EtHg well. The performance evaluation results, trueness (%), repeatability (RSD%) and reproducibility within the laboratory (RSD%), were MeHg 106.4, 8.9, 12.1 and EtHg 87.4, 8.3, 7.6, respectively. It was shown that the method satisfies the performance criteria set by Ministry of Health, Labor and Welfare.

We investigated the process of a bromination reaction of malonic acid (MA) in the Belousov-Zhabotinsky reaction by using a quartz crystal microbalance (QCM). That process involves an enolization reaction of MA as a rate-limiting reaction. We found that the variation of the Br₂ concentration induces a shift of the viscosity and density of the solution in that process. This new finding led us to a determination of the reaction rate constant for the enolization reaction of MA due to the QCM measurement. This value measured by QCM is in good agreement with those measured by a spectrophotometer as described in previous reports. As a result, we succeeded to develop a new measurement method of the chemical reaction.

Inorganic anions, such as bromide, nitrate, phosphate, and sulfate in wakame (Undaria pinnatifida), were determined using ion chromatography (IC). Dried wakame samples were prepared by drying and powdering boiled and salted wakame, whose production districts were clear. The above inorganic anions in the samples were extracted into pure water using ultrasonic extraction prior to IC analysis. Linear discriminant functions were obtained using the PO₄³⁻-P and SO₄²⁻-S results. The misclassification rates of identification were 5.56 and 6.67% for the boiled and salted wakame produced in the Sanriku area and those in China, respectively ; the misclassification rates were 0 and 0% for the wakame produced in the Naruto area and those in China, respectively. Inorganic anions in dried wakame available in the market were similarly determined. The discriminant functions were applied to the analytical results after the SO₄²⁻-S results were corrected using the average concentration ratio for SO₄²⁻-S between the boild and salted wakame and dried wakame purchased in the market. The misclassification rates of identification were 25.0 and 35.7% for the purchased wakame produced in the Sanriku area and those in China, respectively ; the misclassification rates were 12.5 and 35.7% for the purchased wakame produced in the Naruto area and those in China, respectively. The proposed procedure could be useful as a simple screening method to identify wakame production districts.

In this study, the atmospheric concentration of volatile organic compounds (VOCs) was monitored by using passive samplers ; also, the relationship with emissions was investigated. Anthropogenic VOCs, such as benzene, toluene, xylene, ethylbenzene and 1,4-dichlorobenzene, as well as biogenic VOCs, such as α-pinene, were monitored. The concentration of toluene was the highest among these VOCs, and the second highest was α-pinene. The concentration of benzene was below the environmental quality standard in Japan. The sector of emission sources of toluene, xylene and ethylbenzene were implied to be similar because their concentrations showed a high correlation with each other. The concentrations of toluene, xylene and ethylbenzene showed high correlations with the amounts of emissions based on the PRTR database. The concentrations of 1,4-dichlorobenzene and α-pinene showed high correlations with the population and conifer covered area ratio, respectively. It was demonstrated that the atmospheric concentration of VOCs is influenced by emission sources in a relatively short distance.

The protein error in a urine pH measurement by a test strip using mixed indicators of methyl red (MR) and bromothymol blue (BTB) was investigated mainly by a calculation based on the chemical equilibrium. In the pH region that is a part of the visual-transition interval for MR, a positive error occurs, and in the pH region including the visual-transition interval for BTB, a negative error occurs. With increasing pH, the positive error decreases and the negative error increases. The measurement error increases as the protein concentration increases and the concentration of a pH indicator decreases. These calculated results showed the same tendency as a laboratory finding with a test strip.