Kazutake Takada

Use of a piezoelectric quartz crystal as a conductivity detector and its analytical application.

オシレーターから水晶発振子への回路を開き,その部分(電極)を液体に浸しても,水晶発振子は安定に発振し,その際の基本振動数は,電解質溶液に浸した場合には電気伝導度に,又,有機溶媒に浸したときには主に誘電率に依存して変化する.線状電極を電解質溶液に浸した場合には,電気伝導度に比例して振動数が変化し,更に電極間隔が狭くなるほど感度が増加した.従って,この水晶発振子は溶液の電気伝導度や誘電率の検出器として用いることができるので,液体クロマトグラフの電気伝導度検出器として,又,容量分析の終点検出器としての利用を試みた.

Iridium(III) Bis-Pyridine-2-Sulfonamide Complexes as Efficient and Durable Catalysts for Homogeneous Water Oxidation.

A family of tetradentate bis(pyridine-2-sulfonamide) (bpsa) compounds was synthesized as a ligand platform for designing resilient and electronically tunable catalysts capable of performing water oxidation catalysis and other processes in highly oxidizing environments. These wrap-around ligands were coordinated to Ir(III) octahedrally, forming an anionic complex with chloride ions bound to the two remaining coordination sites. NMR spectroscopy documented that the more rigid ligand frameworks-[Ir(bpsa-Cy)Cl2](-) and [Ir(bpsa-Ph)Cl2](-)-produced C1-symmetric complexes, while the complex with the more flexible ethylene linker in [Ir(bpsa-en)Cl2](-) displays C2 symmetry. Their electronic structure was explored with DFT calculations and cyclic voltammetry in nonaqueous environments, which unveiled highly reversible Ir(III)/Ir(IV) redox processes and more complex, irreversible reduction chemistry. Addition of water to the electrolyte revealed the ability of these complexes to catalyze the water oxidation reaction efficiently. Electrochemical quartz crystal microbalance studies confirmed that a molecular species is responsible for the observed electrocatalytic behavior and ruled out the formation of active IrOx. The electrochemical studies were complemented by work on chemically driven water oxidation, where the catalytic activity of the iridium complexes was studied upon exposure to ceric ammonium nitrate, a strong, one-electron oxidant. Variation of the catalyst concentrations helped to illuminate the kinetics of these water oxidation processes and highlighted the robustness of these systems. Stable performance for over 10 days with thousands of catalyst turnovers was observed with the C1-symmetric catalysts. Dynamic light scattering experiments ascertained that a molecular species is responsible for the catalytic activity and excluded the formation of IrOx particles.

Impedance and frequency characteristics of electrode-separated piezoelectric quartz crystals in liquids

Abstract The electrical equivalent circuit parameters of an electrode-separated piezoelectric quartz crystal (PQC), where the gaps between the electrodes and the crystal plate were filled with various liquids, were evaluated from admittance measurements and were compared with those of a normal PQC with Au electrodes adhering to the crystal plate. The resistance parameter in the equivalent circuit of the electrode-separated PQC was more sensitive to the specific conductivity, density and viscosity of liquids than was that of the normal PQC. This parameter, unlike that of the normal PQC, was also affecteded by the permittivity of the liquid. The effect of the liquid properties on the other parameters in the equivalent circuit and the series resonant frequency are also discussed.

Electrochemical control of montmorillonite clay swelling

The swelling–shrinking behaviour of a montmorillonite clay film in aqueous electrolyte solutions has been monitored using quartz crystal resonators. The resistance of the electrically equivalent circuit for the clay-coated resonator, which is increased by the clay swelling, was evaluated through impedance measurements. When NaCl, MgCl2 or AlCl3 were used as the electrolyte, the concentration of cation at which the film swelling occurs (transition concentration) was lower for a cation possessing a larger charge. In an FeCl3 solution, the transition concentration was raised by reducing Fe3+ to Fe2+ electrochemically. Further, in a 10–4 mol l–1 FeCl3 solution, the clay film was swollen by reducing Fe3+ to Fe2+ and was then shrunk by oxidizing Fe2+ back to Fe3+; the swelling–shrinking behaviour was electrochemically controlled.

Piezoelectric admittance-based sensing of electrolyte solutions by montmorillonite clay film-coated quartz-crystal oscillators

Abstract The piezoelectric admittance of quartz-crystal oscillators coated with a montmorillonite clay film or a clay/ poly(vinyl alcohol) (PVA) composite film in contact with an aqueous electrolyte solution has been measured and the possibility of applying the technique to chemical sensing examined. The resistance of the equivalent circuit, which has been conventionally accepted for a piezoelectric quartz crystal, of the clay film-coated oscillator evaluated from the admittance measurement increases with decreasing Na2SO4 concentration, though the dependency is not linear. This change in resistance may be ascribed to changes in the density and/or the viscosity of the clay film, which result from the structural change of the film induced by the cation. The sensitivity is suppressed by composition of the clay film with PVA. The clay/PVA composite film-coated oscillator exhibits lower resistance for a cation with higher valence; the oscillator can measure the equivalent concentration or ionic strength of a cation

Biosensing of an indoor volatile organic compound on the basis of fungal growth

A fungal biosensor plate was applied to assessment of the harmfulness of air polluted by formaldehyde. Alternariaalternata, Eurotiumherbariorum and Aspergilluspenicillioides were used as fungal species. Fungal mycelium length and optical transparency of the biosensor plate were employed as indices of the fungal growth. Formaldehyde in air was detected on the basis of growth inhibition, reflected by suppression of the growth indices. Dynamic range of the measurement was 700-4000 microg m(-3) or broader. Eurotiumherbariorum and Aspergilluspenicillioides were the most suitable fungal species to formaldehyde sensing based on the mycelium length and that based on the transparency, respectively.

Effects of Functional Group Density in Stylene-Divinylbenzene Copolymer Phase and of Supporting Electrolyte Concentration in Aqueous Phase on Performance of Iminodiacetate-type Chelating Resin in Terms of Contribution of Ion-Exchange Mechanism

The effects of the functional group density in the stylene-divinylbenzene copoymer phase and of the supporting electrolyte concentration in the aqueous phase on the perfomance of the iminodiacetate (IDA)-type chelating resin were studied in terms of contribution of an ion-exchange mechanism. High hydrophobicity of the resin having a low functional group density interfered with penetration of aqueous solutions into the resin phase to slow the acid-base reaction and the adsorption reaction. Uptake of the cation in the supporting electrolyte into the resin phase was clearly indicated in each of two acid dissociation reactions. The high concentration of the supporting electrolyte enhanced acid dissociation of the IDA group, and a singly deprotonated species interacting with the supporting electrolyte cation strongly interfered with adsorption by the ion-exchange mechanism, while only slightly interfering with adsorption by the complexation. Both the complexed and ion-exchanged species respectively involving two or more IDA groups were destabilized to reduce the adsorption capacity of the resin having the low functional group density.

Enhanced Retention of Chelating Reagents in Octadecylsilyl Silica Phase by Interaction with Residual Silanol Groups in Solid Phase Extraction of Divalent Metal Ions.

Solid-phase extraction (SPE) of divalent metal ions with a lipophilic and potentially divalent hexadentate chelating reagent (H2L), with which octadecylsilyl silica (ODS), was impregnated with was studied to gain more insight into and develop the potential of this methodology. This is the first time to demonstrate that this reagent as well as other common nitrogen-containing reagents were retained both by adsorption due to hydrogen bonding between nitrogen atoms of the reagent and residual silanol groups in the ODS phase and by simple distribution into the hydrophobic space. An appreciably large amount of this reagent could be retained by the adsorption mechanism even with a relatively thin loading solution. The divalent metal ions of Mn(2+), Co(2+) and Zn(2+) were extracted as 1:1 neutral complexes ([ML]), while Ni(2+) and Cu(2+) as ion-pairs of 1:1 cationic complex ([MHL](+)) with anion in SPE with H2L. The extractability and selectivity were substantially the same as that in liquid-liquid extraction.