BUNSEKI KAGAKU Abstracts

In situ diagnostic techniques for water transport analysis in polymer electrolyte fuel cells (PEFCs) by using magnetic resonance imaging (MRI), atomic force microscopy (AFM), Raman spectroscopy and soft X-ray radiography are presented. MRI visualization revealed that water concentration gradient was established in a polymer electrolyte membrane in an operational fuel cell where electro-osmosis, diffusion, capillary pressure and mass transfer at the membrane-gas interface were inherently involved. Tapping-mode AFM visualized spatially-dispersed hydrophilic clusters on the membrane surface and the cluster size was drastically changed by supplying liquid water to the membrane. Mass transfer process at the membrane-gas interface was one of the rate-determining steps to overall water flux across the membrane under water permeation process and was possibly controlled by effective area for water absorption and desorption on the membrane surface. Soft X-ray radiography was developed for water visualization in catalyst layer and diffusion layer in PEFCs. It was demonstrated that soft X-ray radiography showed high spatial resolution by means of large geometrical magnification and high sensitivity to probe liquid water in the fuel cell, because liquid water has large mass attenuation in low energy X-rays.

The hydration of monovalent alcohols (methanol, ethanol, 1-propanol, 2-propanol and tert-butanol), which are perfectly soluble in water, has been studied by using near infrared spectroscopy by focusing on stretching vibrations of each component at around 7000 cm⁻¹. The absorbance of the band ordinarily does not obey Beer's law because of the presence of intermolecular interactions, e.g. hydrogen bonding. To estimate the spectra of non-ideal solutions, such as water-alcohol mixtures, partial molar absorptivity (PMA) is newly proposed as an extended concept of conventional molar absorption coefficient. A PMA is defined as the concentration differentiation of absorbance. Subsequently, the non-ideal spectral components, called excess partial molar absorptivity (EPMA), are calculated by subtraction between real and ideal molar absorption spectra. EPMA reveals the hidden absorption peaks assigned to different hydrogen-bonding species. By careful examination of PMA and EPMA spectra, strengthening of hydrogen bonding is found in low alcohol range less than a well-known breakpoint at around 25 mass% as a result of hydration to the solute molecules. In a concentration range higher than the breakpoint, water and alcohol tend to be separated into each small domain. These results are common in the monovalent alcohol - water binary mixtures.

We have developed an XRF method for the determination of trace elements in suspended particulate matter. A total of 11 elements (Al, Si, S, Cl, K, Ca, Mn, Fe, Cu, Zn, Pb) were successfully detected from the SPM on an air filter after 6 h of sampling (air volume, 6 m³) by applying secondary targets of Ti, Ge and Mo for the primary X-rays from a Gd X-ray tube. Reference filter samples were prepared by dropping the mixed element standard solutions of known chemical concentrations onto a polycarbonate filter. The obtained calibration curves were linear with square values of the correlation coefficients, R², of 0.9491 - 0.9999 for S, K, Ca, Cr, Mn, Fe, Cu, Zn, Pb. A good matching was observed between the calibration curves and those prepared from standard reference materials of SPM (NIST SRM 2783). The minimum detection limits for S, Zn and Pb were found to be 3.6, 1.0, 3.5 ng cm⁻², respectively, indicating that highly sensitive analyses were possible for these elements by the present method. This analytical method was applied to air monitoring samples measured at Tsuruhashi, Osaka city (Japan). They were conducted four times by the mission of FECOA during 2006 and 2007. The trace-element levels for PM2.5 samples collected every 6 h by an air sampler onto filters for 5 days were determined by the present method. As a result, the diurnal variations of the concentrations (ng m⁻³) of S, K, Ca, Fe, Cu, Zn, Pb in the samples were successfully monitored. Especially, a strong positive correlation was observed between the concentration of S in PM2.5 and SO₂ in air, and an increase in the concentration of sulfur during a west wind was observed. The results suggest that a possible source of sulfur for a PM2.5 sample seemed to exist to the west of the sampling point.

Concerning the colorimetry of nitrite ion induced to azo dye, the influence of the ratio between sulfanilic acid or sulfanilamide and N-(1-naphthyl)etylenediamine and the kinetics for the diazotization and coupling reaction are discussed. The sensitivity of a stepwise method is 23% higher than that using a Saltzmann reagent which is mixture of sulfanilic acid, N-(1-naphtyl)etylenediamine and phosphoric acid. The same sensitivity is 41% higher by using sulfanilamide instead of sulfanilic acid. The diazotization and coupling reaction are second-order reaction. That is, R＝k[sulfanilic acid or sulfanilamide][nitrite ion] and R＝k[diazonium ion][N-(1-naphthyl)etylenediamine] respectively. The coupling reaction rate is about 10-times faster than the diazotization.

In order to determine trace amounts of As, Bi, Sb and Sn in low alloy steels by ICP-OES, the authors investigated a separation and pre-concentration procedure using a co-precipitation technique with manganese(IV) oxide (MnO₂). After dissolving the sample, these analyte elements in the solution were precipitated together with MnO₂ formed by a reaction between Mn(II) and Mn(VII). The collected precipitate was decomposed in a mixed HNO₃ and H₂SO₄ solution together with the filter paper, and heated to fume. Then, the analyte elements were analyzed by ICP-OES. The authors investigated the influence of both coexisting acids and elements on the separation of the analyte elements by co-precipitation so as to optimize the conditions for the analytical procedure. Not only As, Sb and Sn in a HNO₃ solution, but also Bi and Sn in a H₂SO₄ solution could be simultaneously and quantitatively separated from the iron matrix by co-precipitating with MnO₂. Using 41.9 mg of Mn(VII) as the reagent for co-precipitation could prevent a decrease in the recoveries of the analyte elements due to interfering with precipitating MnO₂ by chromium ; accordingly, the authors applied the proposed method to the analysis of samples containing 5-7.5mass% chromium. In determinations of As, Bi, Sb and Sn in certified reference materials, good agreement between the certified values and the analytical values was obtained. The detection limits (3σ of blank values) obtained were sub-μg g⁻¹ levels for all of the analyte elements. Therefore, the authors confirmed that the proposed method was useful for simultaneous determination of trace As, Bi, Sb and Sn in the low alloy steels.

The generation of cavitation through ultrasonic waves can lead to the formation of reactive species, such as · OH and H₂O₂ in aqueous liquids. These short-lived species are capable of effecting secondary oxidation or reduction reactions, which are referred to as sonochemical reactions. This paper reports a new method of cavitation diagnostics with an electrochemiluminescence (ECL) optical sensor for studying any sonochemical activity induced by ultrasonic cavitation. This system has been successfully employed to determine the actual rate production of H₂O₂ and the sonochemical efficiency (SE value) in different sonochemical reactors with frequencies of 28, 45, 100 and 490 kHz, respectively. The SE values were in excellent agreement with results evaluated by potassium iodide (KI) dosimetry. Because of the high sensitivity of this method, the potential modulated ECL sensor was capable of measuring the hydroxyl radical production (in this case hydrogen peroxide) in situ, so as to obtain the spatial distribution of cavitation generated in the ultrasound field.

Boron isotope ratios were analyzed in seven domestic analytical labs for boric acid solutions with various compositions of boron isotope abundances, using an Inductively Coupled Plasma- Quadrupole Mass Spectrometer (ICP-QMS). Five sample solutions with different isotope abundances of ¹⁰B were prepared in the range of 10 to 20% by mixing two boric acid solutions containing natural B and enriched ¹¹B, respectively. Then, the ¹⁰B isotope abundances of each sample were certified by analyzing with thermal ionization mass spectrometry (TI-MS) according to ASTM-C791-04. Results obtained from each lab have indicated good coincidences with TI-MS results. Also, the relative standard deviations of results with ICP-QMS of seven analytical labs were 0.11 to 0.81%. The measurement precision for ICP-QMS would be sufficient in terms of practical use, while taking into consideration a valid requirement required for verifying a depletion of the ¹⁰B isotope abundance in the PWR coolant, while this is greater than a nominal analytical error (relative value : 0.22%) for TI-MS shown in ASTM-C791-04.

The detection performance of a portable ²⁴¹Am ionization aspiration-type ion mobility spectrometer (M90-D1-C, Environics Oy) was investigated with nerve gases, blister agents, blood agents, choking agents and related compounds. The vapors of nerve gases, sarin, soman, tabun, cyclohexylsarin were recognized as "NERVE" after about several seconds of sampling, and the limits of detection (LOD) were < 0.3 mg m⁻³. The vapors of blister agents, mustard gas and lewisite 1, and blood agents, hydrogen cyanide and cyanogen chloride were recognized as "BLISTER" with an LOD of < 2.4 mg m⁻³ and > 415 mg m⁻³, respectively. The vapor of chlorine was recognized as "BLOOD" with an LOD of 820 mg m⁻³. The vapors of nitrogen mustard 3 and chlorpicrin were recognized as different alarm classes, depending on their concentrations. The vapors of nitrogen mustard 1, 2 and phosgene did not show any alarm. As for interference, the vapors of nerve gas simulants, dimethylmethylphosphonate, trimethylphosphate, triethylphosphate, diisopropylfluorophosphate, blister agent simulants, 2-chloroethylethylsulfide, 1,4-thioxane, 2-mercaptoethanol, and 20 organic solvents within 38 solvents examined were recognized false-positively. The patterns of detection sensor channel response values of 6 ion mobility cells and semiconductor cell were compared with the situation of the alarm against chemical-warfare agents.