BUNSEKI KAGAKU Abstracts

The present work described an attempt to apply an anodic-oxidation reaction of free chlorine for the quantitative determination. As a working electrode, polycrystalline platinum disk was mainly used. Cyclic voltammograms exhibited well-defined oxidation wave at about 1.1 V vs. Ag/AgCl. The oxidation wave showed good reproducibility and a linear relationship between the oxidation peak current versus concentration. The electro-oxidation of trace amounts of free chlorine, however, particularly amounts less than 0.028 mmol dm⁻³, was strongly inhibited by the initial formation of platinum oxide in a non-Faradaic reaction. Meanwhile, a reduction wave with reproducibility was observed at about 0.6 V vs. Ag/AgCl, after the sweep direction was switched from anodic to cathodic. The peak current and the concentration showed a linear relationship passed through the origin. Moreover, another reduction wave with reproducibility was observed at about 0.8 V vs. Ag/AgCl in switching potential≧1.45 V vs. Ag/AgCl, the peak current and the concentration also had a linear relationship.

We have developed a pH-imaging microscope that enables visualization of the pH distribution with a minimum 100 micron spatial resolution utilizing a semiconductor pH sensor with multiple minute measurement points. The microscope was evaluated quantitatively, and then applied to the analysis of the surfaces of solid materials. In terms of quantitative evaluation, the pH distribution formed by the release of protons from a single ion-exchange resin was studied. On the other hand, in terms of the analysis of solid materials, a unique surface analysis method utilizing the pH, which is one of the parameters for liquids, was developed by enabling a new type of chemical surface analysis of metals, the hard tissues of humans, and so on.

A simple and rapid analysis of cadmium(II) using a color-responsive polymer membrane, which included 1-(2-pyridylazo)-2-naphthol (PAN) and was made on the cell bottom of a microplate with 96 holls, has been developed. This method has been able to determine 96 samples from 8.9×10⁻⁷ to 1.2×10⁻⁵ mol dm⁻³ within ca. 1 hour. For variation absorbance of a polymer membrane, the average of the absorbance was 0.164±0.008, and the relative standard deviation was 2.43％ for ten repeated experiments. Concerning the interference of coexistent metallic ions, those coloring became low upon the addition of masking agents and a pretreatment by solvent extraction. When a correlation of the determined values in the proposed method and atomic absorption spectrophotometry was investigated using river samples to added Cd^2＋, as a result, a high correlation was obtained between both analytical methods.

A method of direct sampling/tungsten furnace electrothermal atomic absorption spectrometry combined with mixtures of soil and graphite powder has been developed for the determination of trace amounts of Se, Cd, Hg, Pb in soil samples, where these samples are mixed with graphite powder, and are applied to a furnace. Soil samples containing hazardous metals (Se, Cd, Hg and Pb) were mixed with graphite powder at a 1 : 1 ratio in an agate mortar. These mixtures were weighed in a tarred W dish and atomized according to an optimized heating program. These heavy metals in soil samples were determined by using calibration curves obtained with aqueous standard solutions. For measuring Hg in an aqueous standard solution, Pd(NO₃)₂ was used for matrix modification. The limits of detection corresponding to three-times the standard deviation for 5 measurements were as follows : Se 1.6 mg kg⁻¹, Cd 0.026 mg kg⁻¹, Hg 2.2 mg kg⁻¹, Pb 0.041 mg kg⁻¹. The relative standard deviations for the proposed method for soil samples were in the range from 1.7％ for 71 mg kg⁻¹ of Pb, to 19％ for 0.11 mg kg⁻¹ of Cd.

In this study we developed a new analytical method for the determination of sulfur (S) in size classified airborne particulate matter (APM) using inductively coupled plasma atomic emission spectrometry (ICP-AES). The total S concentration was determined by the sum of S in the water-extracted soluble fraction, and the acid digested insoluble residue. A precise analytical result of the S concentration in the APM standard reference material (NIST SRM-1648) could be achieved using this method. We adapted this method to size classified APM samples collected in Tokyo. S concentrations and its solubilities were increased along with decreasing the size of APM. From an analysis of ion chromatography (IC), it became clear that 99％ of S in APM with diameter ＜2 μm was water soluble, and the chemical form was ammonium sulfate {(NH₄)₂SO₄}.

In order to determine rare earth elements (REEs) in seawater by using inductively coupled plasma mass spectrometry (ICP-MS) with an on-line preconcentration column, we used the improved iminodiacetate chelate resin (MetaSEP ME-2) that had a cation-type alkyl group. Its operating conditions were optimized, and the recoveries of REEs and the removal rates of matrix elements were compared with other resins. Ca and Mg were removed more efficiently under a buffer solution of pH 5.0. The removal efficiencies of Ca and Mg using MetaSEP ME-2 were better than those using other resins. We determined REEs in a seawater reference material (NASS-5) with MetaSEP ME-2. The obtained results were in good agreement with the reference values. We applied this method to the determination of REEs in seawater collected from Tokyo Bay, and evaluated the distribution patterns of REEs. Consequently, the positive anomaly of Gd in the small-molecule fraction was observed. The positive anomaly of Gd can be attributed to the outflow of Gd compounds, which are used for a magnetic resonance imaging contrast medium.

An analytical method with a liquid scintillation counting technique for the determination of ⁹⁰Sr in the presence of other elements was developed by deriving a calculation formula to remove their influences. The analysis of ⁹⁰Sr has been performed using the radioactive equilibrium of a generation process of ⁹⁰Y with ⁹⁰Sr separated from a sample. In this study, a new disintegration calculating formula that enable us to remove the influences by the coexistence nuclides to analyze ⁹⁰Sr in highly radioactive liquid wastes of spent-fuel reprocessing plants was derived, and the formula was validated by experimental approaches. It was found that ⁹⁰Sr could be analyzed without any influences when a sample contained nuclides that had a long half life, and the radioactive equilibrium was small enough compared to the generation of ⁹⁰Y. The relative standard deviation of the analysis by the proposed method was equal to, or less than, 3％.

The permeability for oxygen and hydrogen peroxide through a poly(dimethylsiloxane) (PDMS) layer with various thicknesses on a platinum electrode was investigated in order to develop a glucose sensor based on the detection of a reduction current of oxygen, which was consumed by a catalytic reaction of glucose oxidase (GO_x) in the presence of glucose. PDMS layers with various thicknesses were prepared on platinum electrodes by casting various concentrations of the PDMS emulsion. Oxygen and hydrogen peroxide permeated through the PDMS layers on a Pt electrode were detected by cyclic voltammetry in buffer solutions. The PDMS layer allowed us to permeate the oxygen, but also acted as a barrier for the permeation of hydrogen peroxide. The concentration of oxygen in the PDMS layers was roughly estimated by quantitative analysis using an amperometric technique, and was found to be ＞2.5 mM, which is ＞10-times higher than that in an air-saturated buffer solution with 0.22 mM oxygen. Finally, PDMS-modified Pt electrodes combined with a poly(vinyl alcohol) stilbazole quaternized (PVA-SbQ) membrane containing GO_x were fabricated, which were applied to glucose sensing. The incorporation of PDMS layers with oxygen permselectivity to glucose sensing enhanced the current responses for oxygen reduction because of a restriction of the permeation for hydrogen peroxide and the high concentration level in PDMS. However, the response time increased with increasing the thickness of the PDMS layer. Therefore, a PDMS layer with 50 μm – 100 μm is suitable to fabricate glucose sensors based on the detection of oxygen.