BUNSEKI KAGAKU Abstracts

Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) has been expected to be a powerful tool for polymer characterization. MALDI-MS has, however, several problems involving : 1) the optimization of matrix reagents and sample preparation by trial and error, 2) mass discrimination for polymers with a wide molecular-weight distribution caused by mass-discrimination effects on the desorption/ionization efficiency and detector response, and 3) the generation of strong chemical background peaks originating from matrix reagents. To overcome these problems and to develop a reliable polymer characterization technique by soft laser desorption/ionization-mass spectrometry, the fundamental measurement conditions and several applications have been investigated. Fundamental aspects of the subjects were clarified through an investigation of the sample preparation and the implementation of an inter-laboratory comparison of polymer characterization. It has been demonstrated that MALDI-MS would be an effective technique for the analysis of structural changes of polymers during the biodegradation process. For the problem of mass discrimination, a novel data-processing method for a size exclusion chromatography (SEC)/MALDI-MS has been proposed for the determination of an accurate molecular-weight distribution of polymers. To avoid the generation of interfering chemical background peaks caused by the use of matrix reagents, novel ionization platforms for surface-assisted laser desorption/ionization-mass spectrometry have been proposed.

An ultra-high vacuum non-contact atomic force microscope (UHV NC-AFM) has been developed with an original constant excitation cantilever method, adopting the frequency modulation (FM) detection mode. Using this UHV NC-AFM, we have succeeded to take images with atomic resolution. The individual dimmer atoms on the Si(100) 2×1 structure could be observed. The spatial resolution of an NC-AFM image seems to be better than that of a scanning tunneling microscope (STM) image. As for the insulating material, polypropylene chains could be clearly resolved on a polypropylene film. NC-AFM images reproduced the geometrical surface topography better than STM images, so that the possibility to more accurately analyze surface structures was shown by comparing images obtained by NC-AFM with those by STM. In the observing O₂ adsorbed surfaces, the possibility to investigate the state of adsorption could also be mentioned. Based on UHV NC-AFM, a UHV scanning Kelvin probe force microscope (SKPM) has been developed using the gradient of the electrostatic force. Using this UHV SKPM, we observed the surface potential on Ag and Au evaporated Si(111) 7×7 surfaces, and succeeded to visualize the electric potential distribution on the atomic level with a potential resolution of about 10 meV. The atomic potential difference reflects the local electron density on the surface, whereas the average potentials corresponding to the DC levels in potential images reflect the work function value.

The properties of the hydrogen bonding of water-ethanol in alcoholic beverages have not been sufficiently clarified. We investigated possible factors that could affect the hydrogen-bonding structure of water-ethanol on the basis of proton nuclear magnetic resonance (¹H NMR) chemical shifts of the OH of water-ethanol and Raman OH stretching spectra. Not only acids (H^＋ and HA : un-dissociated acids) but also bases (OH⁻ and A⁻ : conjugate-base anions from the weak acids) caused a development in the hydrogen-bonding structure of water-ethanol media. We also demonstrated that the hydrogen bonding was strengthened by chemical components in alcoholic beverages (whiskey, Japanese sake, and shochu). This suggested that hydrogen-bonding donors as well as acceptors in alcohol beverages, which exist as initial components or are gained later on, should cause a promoted proton-exchange between water and ethanol molecules.

A wavelet transformation was applied for amperometric glucose and hydrogen peroxide biosensors. A glucose oxidase was entrapped in a polyion complex membrane that was immobilized on a glassy carbon electrode. Changes in the oxygen reduction current of the glucose biosensor were monitored by the stepwise injection of a glucose solution. By using the wavelet transformation, the current response to glucose and the noise current were clearly separated. The signal-to-noise ratio (SNR) of the wavelet-transformed response to the glucose solution (final concentration, 0.4 mM) was 8-times as large as that of the current response. The lower detection limit (SNR＝2), evaluated from the wavelet-transformed response, was about 260 μM, whereas that evaluated from the current response was 930 μM. A horseradish peroxidase-incorporated polypyrrole membrane was immobilized on an indium tin oxide (ITO) electrode. The reduction current of a polypyrrole membrane was monitored. The lower detection limit (SNR＝2), evaluated from the wavelet-transformed response, was about 20 nM, whereas that evaluated from the current response was 100 nM.

The Japan Society for Analytical Chemistry has developed a group of soil certified reference materials (CRMs : JSAC 0461〜0466), whose concentrations of hazardous metal elements (Cd, Pb, As, Se, Cr and Hg) were certified. The concentration levels of the metals in the CRMs ranged over six levels, from the lowest level of JSAC 0461 (no blending) to the highest level of JSAC 0466 (1500 mg kg⁻¹ level). The CRMs were prepared by applying the master batch method, as follows. At first, approximately the same mass of a kind of powdery metallic compound and dried soil were thoroughly mixed, and then baked (fired) in a furnace at an appropriate temperature to the metal. The fired lumps were pulverized into fine powder to be a base powder. Six kinds of base powders were made for each element. The calculated amounts of the base powders and purified brown forest soil were mixed well to prepare CRMs in designed concentrations. The mixtures were analyzed in order to know their homogeneity. The RSD of the results in elemental analyses (n＝3) of six mixtures for six elements had ranges from 0.4％ at minimum to 3.6％ at maximum. It was sufficient to show that the mixtures were homogeneous. The certified values were obtained from a statistical analysis of the results of an interlaboratory comparison study on the elemental analysis of the powders. Twenty two laboratories participated in this study. The medians of the results were applied for the certified values instead of the averages values, as before, because there was some lower bias in reports from some laboratories.

A portable amperometric acid sensor for determining the titratable acidity of fruits and fruit juices has been developed. The detection is based on the voltammetric reduction of 3,5-di-tert-butyl 1,2-benzoquinone (DBBQ) in the presence of acids. The portable amperometric acid sensor of the dimensions and weight, being 17 (W)×9 (D)×4 (H) cm and 300 g, can be utilized for determining the titratable acidity, ranging from 0.10 to 4.00％ as the concentration of citric or tartaric acid. The relative standard deviations (RSDs) of the repeatability and intermediate precision for determining the titratable acidity of commercial orange juice were 1.88％ (n＝6) and 1.56％ (n＝5), respectively. The titratable acidity in eight commercial fruit juices (4 oranges, 2 grapefruits, and 2 grapes), determined by the potable amperometric acid sensor, was compared with that determined by the conventional potentiometric titration method using 0.1 M NaOH. The correlation coefficient of the both analytical results was 0.989. Moreover, the titratable acidity of Tosabuntan, a kind of shaddocks, was traced during the process of maturation at room temperature by the present sensor.

Patent applications submitted between Jan. 1 of 1982 and Dec. 31 of 2005 and published before Oct. 4 of 2007 have been analyzed to investigate recent developments of analytical laser spectroscopy. Out of 9892 patent publications found through keyword searches, 658 patent applications have been concluded to be relevant. Major laser techniques are fluorescence, absorption, emission, Raman and photoacoustic. Fluorecences pectroscopy has the largest contribution. Absorption and emission spectroscopy follow. The peak in the number of applications occurs around 1996, but a recent increase is remarkable especially among foreign applicants. The difference between domestic applicants and foreign applicants lies largely in fluorescence spectrosopy, especially in its biological applications. If analytical laser spectroscopy is going to be useful for the diagonolysis of disease, this report suggests a need for extended research in this field in Japan.