Showing papers by "Tokyo Laboratory published in 2005"

Determination of diphenylarsenic compounds related to abandoned chemical warfare agents in environmental samples

Abstract: To elucidate the current extent of pollution of the environment with diphenylarsine chloride (DA, Clark I) and diphenylarsine cyanide (DC, Clark II), we have developed analytical procedures using gas and liquid chromatography and employed them to analyze water and soil samples. DA, DC, and their degradation products were extracted with water or organic solvents. Derivatization with n-propanethiol was adopted to achieve higher analytical reproducibility. DA and DC were unstable and decomposed into bis(diphenylarsine)oxide (BDPAO) in water, but only negligibly into diphenylarsinic acid (DPAA) during the 30 days of a stability test. Diphenylarsenic compounds afforded the same product by this derivatization, but their reaction rates varied depending on the starting materials. DPAA had to be treated under acidic conditions at 60 °C to achieve the desired conversion efficiency. Recovery of the thiol derivatives of the diphenylarsenic compounds tested was almost quantitative from water, but only about 50% from soil, reflecting the low extraction efficiency. We applied the method to the analysis of organoarsenic compounds sampled from the water of the drinking well in Kamisu-cho, Ibaraki Prefecture, where the water was thought to have had deleterious effects on the inhabitants. The high level of DPAA was identified as the causative agent. Our analyses of soil samples from Samukawa-cho and Hiratsuka City, Kanagawa Prefecture, where a naval arsenal had previously stood, succeeded in identifying intact DA, BDPAO and triphenylarsine, diphenylarsenic thiol-derivatives, as well as other substances (mustard gas, lewisite). The true magnitude of contamination became evident after these measurements. Copyright © 2005 John Wiley & Sons, Ltd.

Continuous-wave cavity ringdown spectroscopy applied to solids: Properties of a Fabry-Perot cavity containing a transparent substrate

Abstract: Cavity ringdown spectroscopy, or photon-trap spectroscopy for generality, is shown to be applicable to a sample in the solid phase by theoretical and experimental studies. In the technique investigated, a solid in a substrate form having optically flat parallel surfaces is inserted exactly normal to a light beam in a high-finesse optical cavity; the light reflected at the substrate surface is coupled back to the cavity and thus the optical loss is minimized. Thereby the trapping lifetime of photons in the cavity is measured to obtain total optical loss including absorption by the solid sample. As the solid substrate behaves as an extra cavity splitting the original cavity, the trapped photons are susceptible to an interference effect inherent to the triply coupled cavity. To elucidate this effect, the coupling efficiency of the incident light and the trapping lifetime of photons dissipating exponentially were analyzed theoretically for a Fabry-Perot cavity containing a transparent substrate as a model. An experiment was performed on a silicon substrate transparent in the mid-infrared range with a cw optical parametric oscillator based on periodically poled lithium niobate. The optical loss caused by insertion of the substrate was measured to be 2.3 × 10^−4 per round trip, which meets a low-loss requirement of the photon-trap technique. The trapping lifetime of photons was found to depend on the location of the substrate as predicted by theory. By optimizing the experimental conditions, the present technique provides a high sensitivity to optical absorption associated with a trace amount of dopants in solids and adsorbates on surfaces.

Formation of Au(III)-DNA coordinate complex by laser ablation of Au nanoparticles in solution.

Abstract: We discovered that an Au(III)-DNA coordinate complex, Au(III)(DNA-base)2(amine)l, are formed by laser ablation of Au nanoparticles in an aqueous solution containing DNA molecules in the presence of amines and multi-valent cations, where l represents an unknown ligand (either amine or water). Optical absorption spectrum of the solution after laser ablation exhibited a 360 nm absorption peak assigned to ligand→Au(III) charge transfer (LMCT) band of the coordinate complex. The complex is considered to be formed as follows: 1) the DNA molecules are neutralized by binding the multi-valent cations to their negatively charged phosphate groups, and adsorbed on the surface of the Au nanoparticles by a hydrophobic interaction, 2) Au(III) ions are liberated from the Au nanoparticles by laser ablation, and 3) an Au(III) ion reacts with amine and two DNA bases of a DNA molecule into an Au(III)(DNA-base)2(amine)l.

Aggregation and fast diffusion of dye molecules on air–glycerol interface observed by confocal fluorescence microscopy

Abstract: Diffusion processes of Rhodamine 6G (Rh6G) dye molecules dissolved in a small hemisphere drop of glycerol on a cover glass were investigated by using a confocal fluorescence microscope equipped with an objective lens with a high numerical aperture (NA = 1.35). Photon burst signals from Rh6G molecules in the bulk glycerol and on the air–glycerol interface of the hemisphere drop were separately detected at a single molecule level. The analysis of the photon burst signals by a correlation function method reveals that a sizable portion of the Rh6G molecules in the drop are aggregated on the air–glycerol interface and diffuse two-dimensionally on it, while the rest diffuse molecularly in the bulk. The aggregates are found to have a diffusion constant 15 times as large as that of the Rh6G molecule in the bulk glycerol, although the aggregates have a hydrodynamical radius much larger than that of a Rh6G molecule.