BUNSEKI KAGAKU Abstracts

Possibilities of polarizing energy dispersive X-ray fluorescence (EDXRF) spectrometry were fully explored to materialize rapid trace element determinations of soil and sediment samples. The pressed powder pellet technique was adopted for sample preparation because of its simplicity. The trace elements examined were V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Sn, Cs, Ba, La, Ce, Pr, Nd, Pb, and Th. The instrument was calibrated by using 26 reference materials. Compton scatter radiation was used as an internal standard to compensate any matrix effects and operating characteristics of the instruments. The correlation coefficients of the calibration lines were greater than 0.98, with the exception of Co and Pr. The results obtained by the proposed EDXRF spectrometry were compared with those obtained by other methods for around 450 samples. Out of the 20 trace elements examined, the results for 10 elements (Ni, Cu, Zn, Rb, Sr, Nb, Cs, Ba, La, Ce and Nd) obtained by the proposed EDXRF spectrometry compared favorably with those determined through conventional wet chemical methods. In contrast, the results for 5 elements (Cr, Co, Zr, Sn, and Pr) exhibited poor agreements with those obtained by the chemical methods. Among these elements, poor agreements of Cr, Zr and Sn were attributable to incomplete dissolution and/or volatilization losses during chemical treatments based on an acid attack, and therefore we concluded that results obtained by EDXRF are superior over those by chemical methods. In the case of Co, however, overlapping of the Fe Kβ line is responsible for the lower correlation coefficient. Although the results of the other 4 analytes (V, Y, Pb and Th) were not as good as those of the first group, they still appeared to be of practical use, considering the time-consuming and potentially hazardous acid digestion pretreatments.

To establish general-purpose methods and tools for biological experiments on a short time scale is an essential requirement for future research in molecular biology because most of the functions of living organisms at the molecular level take place on a time scale from 1-second to millisecond. Thermal control with on-chip micro-thermodevices is one of the strongest and most useful ways to realize biological experiments at the molecular level on these time scales. Micro-thermodevices, which enable experiments on 1-second to millisecond time scales, have been developed by MEMS technologies. Novel biological phenomena on those time scales have been revealed in experiments by the micro-thermodevices: motion control of a rotary motor protein, F₁-ATPase; quenching measurements of DNA/fluorescent dye conjugate; and experiments of fluorescent protein denaturation. Consequently, the MEMS-based micro-thermodevice has enabled us to probe the parameters of biomolecular phenomena on an extremely short time scale that could not otherwise be achieved. Besides the primary advantages of the high-speed and highly sensitive probing capacity of these devices, other advantages, such as adaptability for mass production and on-chip parallel assay, give potential for reducing the experiment hours. These devices are capable of handling any kind of biomaterial; they do not require any mutations or biochemical treatment of the material itself. Therefore, it can be considered as a general-purpose device. Further study and use of these devices may result in a break-through in the research field of protein analysis at the molecular level, and the devices may eventually act as powerful tools in molecular biology.

In order to determine ammonium ion in river and sea-water samples, we propose a method based on the Berthelot reaction of ammonia with 1-naphthol and dichloroisocyanurate to form an indophenol blue dye, and on the extraction of the blue dye with the octadecylsilyl group bonded silica-gel column (Sep-Pak Plus C18 cartridge). The blue dye could be directly extracted on the Sep-Pak Plus C18 cartridge without the addition of quaternary ammonium ion. The blue dye was also completely eluted with 5.0 mL of acetonitrile solution [80% (v/v)], and the absorbance of the eluate was measured at 730 nm. The relative standard deviation was 3% for 160 μg L⁻¹ of ammonium ion (n = 5) and the detection limit was 4 μg L⁻¹ of ammonium ion. Interference of foreign ions was removed by the addition of EDTA. Good agreements were obtained between the values by this method and by the official method on the analysis of both river and sea water.

A simple and highly sensitive visual determination method for Cr(VI) based on ion-pair solid-phase extraction to a PTFE-type membrane filter has been developed. A colored complex that was formed through a reaction between Cr(VI) and diphenylcarbazide was adsorbed quantitatively under the coexistence of sodium dodecyl sulfate (SDS). The colored filter was sandwiched in between two slide glasses after putting a drop of water in order to prevent discoloration, which was caused by drying the colored filter. The concentration of Cr(VI) was determined through a visual comparison with the color standard. The visual detection limit was 0.3 μg dm⁻³. The calibration curve, assessed with the reflection spectrometric response (540 nm), was linear in the concentration range 0〜4 μg dm⁻³ (r = 0.998). The detection limit, defined as three-times the standard deviation of the reagent blank, was 0.07 μg dm⁻³ in 100 cm³ of the sample solution. The relative standard deviation (RSD) for 0.3 μg dm⁻³ Cr(VI) was 6.0% (n = 5). The proposed method was applied to the determination of Cr(VI) extracted from metallic parts.

The photocatalyzed degradation conditions of dicamba in aqueous titanium dioxide-suspended solution were optimized under sunlight irradiation. The effect of various factors, such as photocatalyst loading, temperature, pH, sunlight intensity and irradiation time on the photocatalytic degradation of dicamba was investigated. The primary photocatalytic decomposition reaction followed a pseudo-first-order kinetic law according to the Langmuir–Hinshelwood model. During photocatalytic degradation, the pseudo-first-order rate constant, k_obs, was 0.173 min⁻¹. The half-lives (t_1/2) and the activation energy (E_a) were 4.0 min and 10 kJ mol⁻¹, respectively. Chloride ions were detected as a end products. The stoichiometric transformation of organic chlorine to chloride ion was observed at a relatively short irradiation time (15 min), and the complete mineralization of organic carbon atoms took place at around the same irradiation time. Phenol, 3-chloro-6-hydroxy-2-methoxybenzoic acid, and 3,6-hydroxy-2- methoxybenzoic acid were identified as intermediate products. The photocatalytic degradation mechanisms were proposed on the basis of the experimental results with a molecular orbital (MO) simulation of the frontier electron density. The solar photocatalytic degradation treatment for the wastewater including dicamba is simple, easy handling and low cost. Therefore, since artificial lamp devices, for example a Hg-Xe lamp, are particularly expensive in local and poor areas, the proposed technique seems to become a very powerful method for treating wastewater including dicamba in those areas.

An electrode covered with chitin-chitosan composite film was constructed to monitor binding between protein and ligand. Chitin, which is one of the extracellular matrixes, was dissolved in an organic solvent of N,N-dimethylacetoamide and 1-methyl-2-pyrrolidone. Because chitosan powder remained undissolved, it was considered to be a reaction field of biomolecule interactions. To examine whether the film was powerful, avidin and biotin were selected as a model of a protein and its ligand. Biotin moieties were introduced to active amino groups of the chitosan with a biotinylation reagent. To evaluate the binding on the film, biotin labeled with an electroactive daunomycin was used as a probe. As a result, an oxidation peak of the labeled biotin decreased. This was because the labeled biotin was held in the binding sites of avidin for biotin not used to be immobilized on a biotin-modified chitosan particle. Consequently, the binding could be monitored on the chitin-chitosan film with high biocompatibility. The procedure becomes a new method to evaluate binding between protein and ligand.

We examined both bismuth content levels in some environmental water samples (tapwater, bottled drinking water and slag obtained by sewage disposal) by inductively coupled plasma mass spectrometry (ICP-MS) and cultured cell toxicity of their compounds by the MTT assay. For ICP-MS, the conditions examined were addition of internal standard (IS), apparatus condition, and determination range, etc. When we examined an IS, the advantage was not clear that the ICP-MS response of the IS candidate elements was very variable. However, the sample induction rate into ICP-MS is more changeable at any time. Since the correction of analytical results was enabled by the addition of IS, Tl-203 was selected for IS, and was used in this study. The determination lower limit was 11 ppt by using 10 ppb Tl. Bi was detected in a few environmental water samples at 20.4 ppt〜6.8 ppb (0.07〜6.83 μg/g original slags), but Bi concentrations of most samples were lower than the determination limit. On the other hand, concerning cell toxicity, the subgallate and free gallic acid affected the lives of cultured cells. Especially, the toxicity of free gallic acid was higher. It has been understood that the toxicity is weakly adjusted by chelating with Bi.

Visual analysis by counting to number of changing color on a microplate was examined using the reaction used for several titration analysis (neutralization titration, oxidation-reduction titration and chelatometric titration). After the addition of a sample to the microplate to which the several concentrations of a standard solution were added with the indicator at the each rows, the numbers of discoloring were changed with the sample concentration. As a result, the numbers of discoloration have changed according to each sample concentration even though the reaction of which titration was used. Moreover, from the result of a comparison with the proposed method and commercial colorimetry, it was able to be confirmed that this method was an effective technique as the reliability of the analytical value.

A fast and simple method for the qualitative identification of brominated flame retardants (BFRs) in polymeric materials using ultrasonic-assisted extraction and liquid chromatography with PDA detection (HPLC-PDA) was developed. The identification of polybrominated diphenyl ethers (PBDEs), decabromobiphenyl (DeBB) was achieved within from 11 min to 19 min using ultraviolet detection in the scanning mode. On the other hand, tetrabromobisphenol A (TBBPA) and ethylenebis(pentabromophenyl) (EBPBP) were detected at 4.0 min and 26 min, respectively. The calibration curves from the peak areas of decabromodiphenyl ether (DeBDE), DeBB, TBBPA and EBPBP were linear with high correlation coefficients (R² = 0.999). The detection limits of DeBDE, DeBDE, TBBPA and EBPBP were 0.1 μg/g for a 3 : 1 S/N ratio. The recoveries of DeBDE in standard plastic samples, which were certified by the GC-MS method (IEC62321 Annex A) ranged from 84% to 125%. The developed method can be applied to the screening of DeBDE in standard plastic samples.