A gas-phase chemiluminescence-based analyzer for waterborne arsenic

We show a practical sequential injection/zone fluidics-based analyzer that measures waterborne arsenic. The approach is capable of differentiating between inorganic As(III) and As(V). The principle is based on generating AsH3 from the sample in a confined chamber by borohydride reduction at controlled pH, sparging the chamber to drive the AsH3 to a small reflective cell located atop a photomultiplier tube, allowing it to react with ozone generated from ambient air, and measuring the intense chemiluminescence that results. Arsine generation and removal from solution results in isolation from the sample matrix, avoiding the pitfalls encountered in some solution-based analysis techniques. The differential determination of As(III) and As(V) is based on the different pH dependence of the reducibility of these species to AsH3. At pH < or =1, both As(III) and As(V) are quantitatively converted to arsine in the presence of NaBH4. At a pH of 4-5, only As(III) is converted to arsine. In the present form, the limit of detection (S/N = 3) is 0.05 microg/L As at pH < or =1 and 0.09 microg/L As(III) at pH approximately 4-5 for a 3-mL sample. The analyzer is intrinsically automated and requires 4 min per determination. It is also possible to determine As(III) first at pH 4.5 and then determine the remaining As in a sequential manner; this requires 6 min. There are no significant practical interferences. A new borohydride solution formulation permits month-long reagent stability.     

Single column trapping/separation and chemiluminescence detection for on-site measurement of methyl mercaptan and dimethyl sulfide

A simple, automated method for the measurement of methyl mercaptan (CH3SH) and dimethyl sulfide (DMS) has been investigated. These two sulfur gases have strong and unpleasant odors. The collection and separation are performed in sequence with a single short column packed with silica gel powder. CH3SH and DMS are separated according to their desorption temperatures and introduced into a chemiluminescence cell in this order. These two gases emit strong chemiluminescence by reaction with ozone. The calibration curves obtained are linear, which is superior to flame photometric detection of these substances. The whole system, including a small cylinder for the carrier nitrogen, can be set in a portable box. The instrument is applicable to breath odor analysis, and automated measurement of room air can also be performed. In toilet air analysis, it was observed that levels of the sulfur gases increased after dark. With this instrument, sulfur gases at a ppbv level are successfully measured by a simple procedure without much interference.     

Measurement of ammonia in human breath with a liquid-film conductivity sensor

Measurement of breath NH3 is of interest in clinical applications as it can be used as a measure of kidney/liver functions as well as halitosis. We have developed a liquid-film conductivity sensor to measure NH3 in human breath. A film of dilute H2SO4 is formed on the top of two metal capillary tubes placed in a concentric annular arrangement. The tube exterior has been specially treated to render it hydrophilic. As breath passes over the sensor tip, the film collects NH3 and the solution conductivity (measured by the concentric capillaries functioning as electrodes) decreases accordingly. This initial rate of conductivity decrease was determined to be the best metric (most rapid and least dependent on breath pCO2) for ammonia, relative to time to attain complete neutralization (conductivity minimum) or the final rate of conductivity increase as more ammonia dissolves after neutralization. The absorbing solution composition was optimized so that CO2 does not interfere. Both dynamic measurement using mask sampling and offline balloon sampling were performed. Ammonia readily absorbs on surfaces when significant concentrations of water vapor are present. As such, memory effects are common when analyzing human breath for ammonia. This problem was successfully eliminated. The results from this sensor agreed well with data obtained by a solution-phase fluorometric technique using a porous membrane diffusion scrubber and o-phthalaldehyde derivatization chemistry. For breath CO2 measurement, the applicability of a similar sensor that relies on a NaOH film was also demonstrated.     

Single crystal PMN-0.33PT/epoxy 1-3 composites for ultrasonic transducer applications

Lead magnesium niobate-lead titanate 0.67Pb (Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.33PbTiO/sub 3/ (PMN-0.33PT, abbreviated as PMN-PT) single crystals were used to fabricate PMN-PT/epoxy 1-3 composites with different volume fractions of PMN-PT ranging from 0.4 to 0.8. The electromechanical properties of the 1-3 composites were determined by the resonance technique. Theoretical modeling of the 1-3 composites matched quite well with the measured material properties. It was demonstrated that the thickness electromechanical coupling coefficients of the composites could reach as high as 0.8. A 2.4 MHz plane ultrasonic transducer was fabricated using a PMN-PT/epoxy 1-3 composite with 0.37 volume fraction of PMN-PT. It shows a -6 dB bandwidth of /spl sim/61% and an insertion loss of -14 dB.     

Synthesis of polymer particles with specific lysozyme recognition sites by a molecular imprinting technique

To prepare silica beads covered with a lysozyme‐imprinted polymer layer, we polymerized acrylamide and acrylic acid or acrylamide and N,N‐dimethylaminopropylacrylamide with (NH₄)₂S₂O₈ in a phosphate buffer containing the lysozyme, surface‐modified silica beads, and crosslinkers; the result was the formation of a polymer layer with a lysozyme recognition site on the silica‐bead surface. By quantitative analysis of the supernatant of the solution containing the silica beads, we confirmed that modified silica beads, in contrast to unmodified silica beads, can selectively adsorb lysozymes. The process of binding and releasing the lysozyme to and from the modified silica beads can be repeated several times without degradation of the rebinding ability. A quartz‐crystal microbalance sensor fabricated with a molecularly imprinted polymer layer with a lysozyme recognition site was prepared. When a lysozyme aqueous solution was added to the solution in which the sensor was immersed, a high level of sensitivity and response was observed. High selectivity was also demonstrated by tests with other protein solutions. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3378–3387, 2001     

Influence of KClO3 Addition on the Magnetic Properties and Microstructural Morphology of Y(1−0.2x)Ba(2−0.2x)KxCu3Oy (x = 0 ÷ 0.40) Polycrystalline HTSC

The influence of KclO ₃ addition on the AC complex susceptibility (ac) and microstructural morphology of YBCO HTSC with nominal composition Y _(1–0.2x) Ba _(2–0.2x) K _x Cu ₃ O _y (x = 0 ÷ 0.40) were investigated. Xac was recorded as a function of temperature and of the concentration of KClO ₃ in various AC magnetic fields up to 19 Oe. The data were analyzed using the relation h = a(1 – T _m /T _c ) ⁿ . The results obtained showed that the presence of K- and Cl-containing impurities on the grain boundaries change the intergranular coupling and, within certain concentration limits, improves the superconducting parameters.     

Structural and electrochemical behaviors of metastable Li2/3[Ni1/3Mn2/3]O2 modified by metal element substitution

Layered metastable lithium manganese oxides, Li_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ (x = y = 1/36 for M = Al, Co, and Fe and x = 2/36, y = 0 for M = Mg) were prepared by the ion exchange of Li for Na in P2-Na_2/3[Ni_1/3−xMn_2/3−yM_x+y]O₂ precursors. The Al and Co doping produced the T^#2 structure with the space group Cmca. On the other hand, the Fe and Mg doped samples had the O6 structure with space group R-3m. Electron diffraction revealed the 1:2 type ordering within the Ni_1/3−xMn_2/3−yM_x+yO₂ slab. It was found that the stacking sequence and electrochemical performance of the Li cells containing T^#2-Li_2/3[Ni_1/3Mn_2/3]O₂ were affected by the doping with small amounts of Al, Co, Fe, and Mg. The discharge capacity of the Al doped sample was around 200 mAh g⁻¹ in the voltage range between 2.0 and 4.7 V at the current density of 14.4 mA g⁻¹ along with a good capacity retention. Moreover, for the Al and Co doped and undoped oxides, the irreversible phase transition of the T^#2 into the O2 structure was observed during the initial lithium deintercalation.     

Indentation-induced ductile behavior of glass–ceramics involving layered aluminosilicates

Contact damage in materials is critical in engineering applications because it influences mechanical resistance, such as wear, erosion, and impact failure. Indentation tests were performed using a tungsten carbide ball indenter (Hertzian contact) on the surfaces of glass–ceramics containing hexagonal CaAl₂Si₂O₈ or mica crystals (fluorophlogopite), both of which have a layered structure. The stress–strain relation and the permanent deformation on the surface, as well as the observation of the microcrack zone by X-ray computed tomography using synchrotron radiation, revealed that the glass–ceramic with hexagonal CaAl₂Si₂O₈ showed ductility similar to the quasi-plastic behavior previously observed in the mica glass–ceramic. The yield stresses of the glass–ceramics were estimated from the stress deviating from the stress–strain relation assuming complete elastic response between the ball and the sample. The ratio of the yield stress to Young modulus (Y/E) of the glass–ceramic with hexagonal CaAl₂Si₂O₈ was determined to be higher than that of the mica glass–ceramic.     

Study of polycarbonate–polystyrene interfaces using scanning transmission electron microscopy spectrum imaging (STEM-SI)

Polymer blends are important for both commercial utility and scientific understanding. The degree of interfacial mixing in polymer blends is important since it influences the blends' mechanical properties. Understanding bulk properties in multiphase polymeric materials requires knowledge of the interfacial properties of the materials. The characterization of the interface, in terms of its width and composition profile, provides insight about the bulk behaviour of the material. Chemical microscopy through electron energy-loss spectroscopy (EELS) in a transmission electron microscope is gaining popularity to characterize narrow polymer–polymer interfaces. In this work, we show how scanning transmission electron microscopy spectrum imaging, a spatially resolved energy-loss spectroscopy, can be employed to calculate the interfacial width in a pair of immiscible polymers, taking a polycarbonate–polystyrene (PC-PS) bilayer as an example. By mapping peaks unique to each of the blend constituents at several points across the interface, we show how the interfacial profile concentrations can be determined. With this method we calculated the interfacial width in the PC-PS bilayer sample to be approximately 32 nm, even utilizing low resolution spectrometers, which are more widely available. Using the technique described with higher resolution EELS instruments having a better signal-to-noise ratio, a higher spatial resolution can be achieved. Using EELS chemical fingerprints of polymers that have been developed earlier, the technique presented here has the potential for effective visualization and morphological measurements of phase-differentiated polymer blends. This paper is an attempt to enable a new user to characterize polymer–polymer interfaces using chemical microscopy. © 2022 Society of Industrial Chemistry.     

A White LED Driver Using a Buck–Boost Converter

For mobile backlighting applications, a white LED (WLED) driver using a buck–boost converter is proposed in this letter. Unlike conventional converters using boost converters, 2×/1.5× charge pumps, and so on, the proposed converter offers the negative stepped‐down voltage to drive the LED's cathode only when the input voltage is insufficient to drive a 1× transfer mode. Furthermore, unlike the LED backlight using charge pumps, the proposed converter can adjust the output voltage by controlling the duty factor of the clock pulse. Thus, the proposed converter can realize high power efficiency. The validity of the proposed converter is confirmed by simulations and experiments. © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.