The progress of laser technology has brought extensive applications of nonlinear optical (NLO) spectroscopy to analytical fields. Especially, optical second harmonic generation (SHG), which is one of the most popular NLO phenomena, has been successfully applied to the study of interfaces (surfaces). Several fine reviews on surface SHG spectroscopies have appeared recently. The present article will concentrate on some new applications of SHG: second harmonic microscopy (SHM) for microstructural characterization, SHG interferometry for the determination of absolute molecular orientation, surface analysis of microstructures, and some molecular interactions at the interfaces.
The electrochemical behavior of a cobalt(II)-heptacyanonitrosylferrate (CoHNF) film on a glassy carbon electrode has been investigated. Cyclic voltammetry shows a single electron-transfer reaction taking place at 0.51 V for the modified electrode. The ion effect of the supporting electrolyte indicates that the ion permeability in the CoHNF film is mainly determined by the hydrated radius of cation. The modified electrode catalyzes redox reactions of the Fe2+/Fe3+ couple. It also exhibits a linear potentiometric response over the range of 3×10-5 - 1×10-2 M NO2- with a near-Nernstian slope in an acidic medium.
The voltammetric responses of dopamine (DA) and ascorbic acid (AA) at a deactivated polythiophene (PT) film modified electrode were investigated. It was found that DA displays nearly identical voltammetric response at both a bare and the modified electrode, while the voltammetric signal of AA is greatly suppressed at the modified electrode due to the repul-sion between it and the deactivated film. Various experimental parameters affecting the voltammetric responses of DA and AA were studied. The modified electrode was demonstrated to be very useful in selectively determining DA in a mixture of DA and AA. At a 0.5 μm deactivated PT film modified electrode the calibration curve of DA was linear over the range of 0.8 μM - 1.0 mM in the presence of 1.0 mM AA. The detection limit was 0.4 μM.
The pyrazole-containing 18-membered crown ether 1, which possesses a less-bulky substituent on the sp3 nitrogens and not only the sp2 nitrogen, but also the carbonyl groups as ligating points, exhibited excellent ability as an ionophore for a NH4+-selective electrode. The value of the selectivity coefficient of an ion-selective electrode (ISE) containing 1 for the NH4+ ion with respect to an interfering K+ ion was 6.3×10-2. This result is superior to that of ISE based on an antibiotic substance, nonactin (1.2×10-1).
A non-conducting polymer film of phenol and its derivatives, in which glucose oxidase (GOx) was immobilized, has been prepared on a carbon paste electrode containing ferrocene by electrochemical polymerization. Five phenol derivatives (phenol, 3-aminophenol, 3-methylphenol, 3-nitrophenol, and 1,3-dihydroxybenzene) were examined; 3-aminophenol was found to be the most suitable monomer for the fabrication of amperometric glucose sensors. The maximum current Δimax obtained from the Eadie-Hofstee form of the Michaelis-Menten equation decreased with increasing the substituent constant σm; a plot of Δimaxvs.σm gave a straight line except for 3-aminophenol. In the case of 3-aminophenol, both hydroxyl and amino groups participated in the electropolymerization and consequently larger amounts of GOx may be immobilized in this polymer film. This behavior resulted in the higher sensitivity to glucose. The response currents of Fc,CP/GOx/PAPO, which was fabricated by cycling between 0.20 and 1.40 V vs. Ag/AgCl for the electropolymerization of 3-aminophenol, changed little within a period of 40 d. In addition, this glucose sensor could minimize contributions from the easily oxidizable compounds, uric acid and L-ascorbic acid.
A simple, rapid and sensitive iodometric amplification method has been developed for the determination of microgram amounts of MnII, MnVII, CrIII and CrVI. The method is based on the prereductions of MnVII and CrVI with Na2SO3, the oxidations of both MnII and CrIII in the absence of Na4P2O7 and the oxidation of only MnII in its presence with excess periodate in acetate buffer (pH=3.0), removal of the unreacted periodate by masking with molybdate and the subsequent titration of liberated iodine after adding iodide. The individual amounts of MnII, MnVII, CrIII and CrVI in different test solutions were successfully determined by this method, which offers 20-fold and 12-fold amplification for Mn and Cr, respectively.
Admicelles formed on alumina were studied from the viewpoint of separation vehicles in trace analysis. Gamma-alumina (1.5 g) was suspended in 40 cm3 of water and mixed with 10 cm3 of ammoniacal solution containing 1.5 mg of dithizone and 100 mg of sodium dodecyl sulfate. The mixture was acidified to pH 2, where the anionic surfactant was strongly adsorbed on the positively charged alumina surface to form dithizone-impregnated admicelles. Metal contaminants in the admicelles were thoroughly removed by washing with 4 mol dm-3 nitric acid. The quantitative adsorption from water was performed at pH 2 - 9 for Cu, pH 3 - 9 for Pb and pH 4 - 9 for Co, Ni and Cd. For seawater, simultaneous collection required adjusting the pH to ca. 8. Humic and fulvic acids did not interfere with the separation. The admicelle column was substantially stable during adsorption and desorption, which allowed the same column to be used at least three times. The proposed method was combined with inductively coupled plasma-mass spectrometry for the analysis of seawater.
The evaluation of the applicability of chitin and chitosan as a sorbent material to solid phase extraction of phenol and chlorophenols was made by using high-performance liquid chromatography (HPLC). For the measurement of the adsorptive capabilities, adsorption isotherms as well as breakthrough curves were obtained by means of batch experiments or column experiments respectively. The increasing tendency of the amount of adsorption with the number of chlorine atom in phenol molecules was observed for both chitin and chitosan. The driving force of the interaction could be attributed to hydrogen bonding among electro-negative atoms in chitin, chitosan or chlorophenols.
The synergistic extraction of gallium(III) and indium(III) with 2,4-pentanedione (Hacac) in heptane and carbon tetrachlo-ride has been studied using 3,5-dichlorophenol (DCP) as the synergist. A remarkable enhancement of the extraction of both metals(III) with 0.01 mol dm-3 Hacac was observed upon the addition of 0.05 mol dm-3 DCP, especially in heptane. From an extraction-equilibrium study, the synergistic enhancement was ascribed to the formation of outer-sphere complexes, M(acac)3·n(DCP) (M=Ga or In; n=1 - 3), in the organic phase. Furthermore, using the synthetic metal(III) chelates hydrogen-bond formation between M(acac)3 and DCP was observed by IR and 1H NMR in carbon tetrachloride. The effect of DCP on the separation efficiency of gallium(III) and indium(III) from aluminium(III) was discussed by means of the equilibrium constants such as the formation constants of outer-sphere complexes as well as the extraction constants obtained so far. It was concluded that the present synergism caused by outer-sphere complexation improved not only the extraction efficiency, but also the separation efficiency of those metals(III).
The solvent extraction of lanthanum(III), praseodymium(III), neodymium(III), samarium(III), europium(III), gadolini-um(III), thulium(III), ytterbium(III), lutetium(III), scandium(III), and indium(III) (M(III)) in 0.1 mol dm-3 sodium nitrate solutions with 4-isopropyltropolone (Hipt) into chloroform was studied. From the dependence of extraction on the concentration of 4-isopropyltropolonate anions in the aqueous phase and also on the concentration of metal ions, it was concluded that scandium(III) and indium(III) were always extracted in the mononuclear form, M(ipt)3. But dinuclear lanthanoid(III) chelate complexes, M2(ipt)6·nHipt where n=0 or 1, were also extracted with mononuclear ones even when the metal concentration in the organic phase was higher than about 10-6 mol dm-3. The degree of dinuclear species formation was greater in the following order: lutetium(III) to samarium(III)>neodymium(III)>praseodymium(III)>lanthanum(III)»scandium(III) - indium(III). On the other hand, the stability of the self-adduct dinuclear chelate complexes in the organic phase was higher in the order: lanthanum(III) to gadolinium(III)>thulium(III)>ytterbium(III)>lutetium(III).
A new analytical method estimating horseradish peroxidase (HRP) activity for the enzyme immunoassay (EIA) has been developed by using ESR spectroscopy. The optimal conditions sensitively determining HRP activity: buffers, pH, and temperature, have been investigated by using p-acetamidophenol (p-AP) as the substrate of HRP. An appropriate hydroxylamine was used as a trapper of the p-AP radical, which can be converted into a stable nitroxide by a redox reaction with the radical derived from the substrate. The sensitivity of the HRP activity determined by ESR measurement of the nitroxide thus generated is 19 to 25 times higher than those of conventional luminometry and colorimetry assays. Typical applications of the method to Thyroid Stimulating Hormone and glucose assays are also presented to show the usefulness of the method.
The effect of cationic components in liposome on the bioluminescence (BL) intensity from the firefly luciferin-luciferase reaction with ATP was investigated by use of vesicles formed by the extrusion technique (VET). Stearyltrimethyl-ammonium chloride (STAC), stearylamine (SA) and tetracaine (TC) were used as cationic components. The VET containing STAC and SA enhanced the maximum BL intensity. In contrast, a lowering of the maximum BL intensity was observed in the presence of the VET containing TC. The sensitivity for ATP in the presence of the VET containing STAC was improved by a factor of 2 and 10 times compared to that in the presence of the VET containing SA and that in water alone, respectively. The differences in the BL enhancement between cationic components could be explained in terms of different membrane surface potentials of the VET containing these cationc components.
A certified reference material for organotin analysis (NIES CRM No. 12 Marine Sediment) was prepared at National Institute for Environmental Studies. The starting material was a surface sediment sampled at the center of Tokyo Bay in 1989. The chemical and physical properties of the material indicated homogeneity of this CRM at practical level. Certified values are given for tributhyltin (0.19±0.03 mg TBT/kg dry wt.) and total tin (10.7±1.4 mg/kg dry wt.) contents and a reference value for triphenyltin (0.008 mg TPT/kg dry wt.) based on the analytical results from collaborative analysis. The organotin levels in this CRM are higher than the current average level of, but within the range of, TBT and TPT found in marine sediment along the Japanese coast. This CRM will be of practical value in the quality assurance of organotin analysis in marine environmental monitoring programs.
Separation characteristics of aminopropyl silica gels modified with copper-phthalocyanine (Cu-PCSD) were investigated in comparison with those of a pyrene stationary phase (PYE). By the use of alkylbenzenes as samples, we have found that the π-π electron interaction is dominant in the separation mode of a column packed with Cu-PCSD, while the hydrophobic interaction with alkyl groups participates in the separation mode of a PYE column. The separation factor (αn′+1) of a polyaromatic hydrocarbon (PAH) having n′+1 aromatic rings by a PAH having n′ aromatic rings is larger than that obtained from the PYE column. In particular, when n′ is 3, αn′+1 is more than 6 times that of the PYE column in the maximum value. In addition, the planar recognition ability of the Cu-PCSD column is much better than that of the PYE column. The above results indicate that the separation characteristics of Cu-PCSD are mainly due to the π-π electron interaction based on Cu-PCS bound in parallel to the surface of the aminopropyl silica gel.
An improved apparatus for dual-flow countercurrent extraction was manufactured, and its efficiency was determined by graphical stage calculations. The apparatus, which had six extraction cell units, was found to have more than 5.5 plates.
The chemical shift of the characteristic fluorescence X-ray emission line is far smaller than the resolution of a detector widely used in energy-dispersive spectroscopy, such as a Si(Li) detector. The line position measured with this kind of detector greatly depends on many factors. In the present work, an energy-dispersive X-ray spectroscopy method was introduced to precisely measure the chemical shift of the characteristic X-ray emission line by partitioning the measurement time into many subdivisions with a statistical data-processing procedure. The possibility of this method was also considered theoretically. The chemical state of an element could be identified by using a reference material. The discrimination limit was found to be less than 0.3 eV if electric signal processing could be carefully controlled.