Steady-state and picosecond time-resolved fluorescence spectroscopies were conducted to study excited state properties of 1-anilino-8-naphthalene sulfonate (ANS) in reverse AOT (sodium bis(2-ethylhexyl)sulfosuccinate)/isooctane micelles. The maximum wavelength, quantum yield, and lifetime of ANS fluorescence were determined as a function of the micelle size. Detailed analyses of these photophysical parameters demonstrated that the energy gap between the ground and excited states of ANS decided the nonradiative decay rate constant (knr). On the basis of both energy gap dependence of knr and micelle size effects on the photophysical parameters of ANS, the characteristic fluorescence behavior of ANS in the reverse AOT micelles was discussed in terms of the structures of water molecules: bound- and free-water.
Using a wet-chemical method based on flow-coulometry, an analytical method to measure unstable ions of copper, CuO+ and Cu+, in superconductors has been advanced. The distributions of these ions from the surface to inside of sample discs were determined by the developed method. The sample discs, which were prepared by the ceramic method, contained a lower CuO+/Cutotal ratio at the outermost surface, and gradually increased to a depth of 200 µm. On the contrary, the Cu+/Cutotal ratio in a YBa2Cu3O6 sample was almost homogeneous. The positively electrolyzed La2CuOy disc as an electrode exhibited a much higher oxidation state than that without electrolysis. It was confirmed that the CuO+/Cutotal ratio on the surface and in the bulk of the electrolyzed La2CuOy had an influence on the superconducting characteristics.
A simple and rapid method for the in situ preconcentration of trace dissolved sulfide in environmental water samples has been developed based on solid-phase extraction using Sep-Pak C18 cartridges. Dissolved sulfide in water samples, which was taken into a graduated syringe to prevent the oxidation of sulfide by air, was reacted with N,N-dimethyl-p-phenylene-diamine sulfate and iron(III) chloride to be converted into Methylene Blue immediately after sample collection. The formed Methylene Blue was adsorbed on Sep-Pak C18, which was stable on Sep-Pak C18 for at least 30 d. The adsorbed Methylene Blue was eluted with a mixture of methanol and 0.01 M hydrochloric acid. The color intensity due to the Methylene Blue was measured at 659 nm. The proposed method is applicable to brackish and sea water samples as well as freshwater.
2-Hydroxyimino-3-(2-hydrazonopyridyl)-butane (HHB) was investigated as a new reagent for the flotation of palladium(II). The metal ion forms a 1:1 pale-violet complex with HHB in aqueous solution. An intense clear violet layer was formed, after flotation, by adding an oleic acid (HOL) surfactant. The composition of the float is 1:1 (Pd:HHB). A highly selective and sensitive spectrophotometric procedure was proposed for the determination of microamounts of Pd(II) as its floated complex. The flotation-determination method was achieved in the pH range 2.5 - 7.0. Beer’s law was obeyed up to 6×10-5 mol l-1 (6.3 ppm). Interference from various foreign ions was avoided by adding excess HHB. The molar absorptivities of Pd-HHB and Pd-HHB-HOL systems are 2.5×103 and 2.1×104 l mol-1 cm-1 at 555 nm, each. The formation constants of the species formed in the presence and absence of HOL are 9×105 and 4.6×107 l mol-1, respectively. The method was successfully applied to the analysis of Pd(II) in simulated ores, complexes, and water samples. The separation mechanism is discussed.
The extraction equilibria of copper(II) with 2-bromoaliphatic carboxylic acids and with conjugated carboxylic acids in benzene were investigated using a curve-fitting method in order to grasp the bonding character of a functional carboxyl group. A monomeric species, CuL2(HL)a, together with dimeric copper(II) carboxylate Cu2L4(HL)2 was extracted in the concentration region of copper(II) in the organic phase, CCu,o>3×10-5 mol dm-3. A new linear relationship between the extraction constant (Kex) and the acid dissociation constant (Ka) was empirically obtained as log Kex(11)=1.74log Ka-0.75 (1) for CuL2·HL and log Kex(12)=1.37log Ka-1.97 (2) for CuL2(HL)2, as well as log Kex(22)=1.71log Ka-3.17 (3) for the dimer. Thus, we can obtain an approximate value of the dimerization constant of copper(II) (Kdim(a,2)) in the organic phase from Ka by log Kdim(a,2)=log Kex(22)-2log Kex(1a) (a=1 or 2), except for cases of conjugated carboxylates, which deviate from Eq. (3), due to a lower log Kex(22). The deviations would be correlated to the change in the dipole moment affected by electronic delocalization with resonance over the conjugated ligand in the bridging form. Therefore, the extraction of a monomer together with a dimer is easily found by using carboxylic acids of low pKa or of a conjugate.
A method for the determination of ethanol using alcohol oxidase (AOD), peroxidase (POD), and 2,2′-azino-bis(3-ethyl-benzthiazoline-6-sulfonic acid) (ABTS) was developed in which those enzymes were separately immobilized on the inside surface of each well of a 96-well microtiter plate. Prior to immobilization, the surface was activated with glutaraldehyde. The activation conditions remarkably affected the activity of the immobilized AOD. A sample solution containing ethanol was first added into the well with immobilized AOD (AOD-well). After 30 min, an aliquot (20 µl) was transferred into the well with immobilized POD containing 180 µl of 2 mM ABTS and the absorbance change at 415 nm for 10 min was measured with a microplate reader. The calibration curve was linear over the range 0.10 - 1.0 mM, and the relative standard deviation (n=5) was 0.8% for 1 mM ethanol. The ethanol concentration in alcoholic beverages, obtained by the present method, agreed well with that by the F-kit method. The AOD-well was reusable for 20 successive determinations.
Capillary electrophoresis was applied to the separation of C12 - C18N-acyl-L-glutamates surfactants, used for cosmetic ingredients. Using the aqueous buffer of 10 mM borate at pH 9.2, unstable mobility and peak-broadening of the surfac-tant ions were observed. The effect of addition of organic solvents to the borate buffer system was investigated by means of the determination of electrophoretic mobility and zone width of the solutes. The results indicated that the addition of methanol, capable of hydrogen bonding, was more effective than that of acetonitrile to avoid micelle formation of the surfactant and to stabilize the electrophoretic behavior. An optimized condition was established by adding 15%(v/v) methanol to the borate buffer. The application to a cosmetic product was also briefly examined using the optimized condition.
Cyclosporin A (CsA) is a potent immunosuppressant widely used in human medicine to prevent rejection of transplanted organs. Total concentration of CsA and its metabolites in human blood was determined by pyrolysis mass spectrometry (pyr-ms). Mass to charge (m/z) values of 100 of CsA and 3-nitroaniline as an internal standard were used for quantitative measurements by selected ion monitoring (SIM). Results of pyr-ms at 420°C are highly reproducible. Limit of detection (LOD) and linearity were determined to 0.7 ng ml-1 and 0.7 ng ml-1 - 100 mg ml-1 , respectively. LOD is improved to 0.02 ng ml-1 by using a solid phase extraction (SPE) disk. Results of pyr-ms are compared with those obtained by the high performance liquid chromatography (HPLC) measurements.
Phenol-formaldehyde mixtures are widely used in a variety of applications, such as flame-retardant or adhesives. This kind of resin can also be used as surface protecting polymers for glassy carbon electrodes when they are applied to phenol oxidative processes. The purpose of this work was to obtain the best conditions for phenol (and two derivatives) determi-nation with a phenol-formaldehyde modified glassy carbon electrode in flow injection analysis (FIA) with amperometric detection and to compare these results with those obtained with two different modifiers, 4-hydroxybenzaldehyde and 4-hydroxybenzoic acid, under the same conditions. Linear relationships were obtained in the 0.1 to 1.0 µM phenol (or derivative) concentration range, the optima experimental conditions being 1.11 ml min-1 , 0.700 V (vs. Ag/AgCl/NaCl 3 M), with an electrodeposited charge of the modifier of 1.10 C cm-2 and using an aqueous buffer (0.10 M total phosphate+ 0.05 M KCl, pH=7.0) as carrier solution.
A chemiluminescence method for the determination of tetracyclines was developed. The method is based on an enhancement of tetracyclines upon the chemiluminescence light emission of tris(2,2′-bipyridine)ruthenium(II). In a sulfuric acid medium, chemiluminescence light emission is generated upon continuous oxidation of tris(2,2′-bipyridine)ruthenium(II) by potassium permanganate, catalyzed by Mn(II). The light-emission intensity is enhanced when the tetracyclines are also present in the reaction system. Under the optimum conditions, the calibration curves are linear over the range 1.0×10-7 - 1.0×10-5 g/ml for tetracycline, 4.0×10-8 - 1.0×10-5 g/ml for chlortetracycline and 1.0×10-7 - 1.0×10-5 g/ml for oxytetracycline. The limits of detection (S/N=3) are 2.0×10-8 g/ml for tetracycline, 1.0×10-8 g/ml for chlortetracycline and 2.0×10-8 g/ml for oxytetracycline. The proposed method was used to determine tetracyclines in pharmaceutical formulations with good results.
The electrochemical behavior of Co2+, whose response is abnormally enhanced at DNA-modified gold electrodes in the presence of 2,2′-bipyridyl, was found. After it forms an adduct with Co2+, excess 2,2′-bipyridyl can enhance the electro-chemical response of this adduct at DNA-modified gold electrodes by synergism. ssDNA-modified gold electrodes that are highly sensitive to Co2+ were utilized to determine trace Co2+ in the presence of 2,2′-bipyridyl by cyclic voltammetry. It was found that the peak currents for cobalt increase linearly over the concentration range of 1.0×10-7 - 1.1×10-6 mol/l with a detection limit of 4.0×10-8 mol/l. For seven preconcentration/voltammetric detection/renewal cyclic experiments with 1.0×10-7 mol/l and 1.0×10-6 mol/l Co2+ solutions, relative standard deviations of 2.7% and 1.9% were found, respectively, indicating that the DNA-modified gold electrodes were stable and repeatable.