Electrochemical behavior of benzo[c]cinnoline-N-oxide was studied. Two discrete 2 and 4 electron reduction waves in acidic media but only one wave in basic media were observed in ethanol-BR buffer system (1:5 v/v). The number of electrons transferred and the difussion coefficient were determined by using various voltammetric techniques, such as sampled current polarography, cyclic voltammetry, chronoamperometry, chronocoulometry and constant potential coulometry. Adsorption of the molecule on the surface of the mercury drop was analyzed and this phenomenon was exploited to calculate the diffusion coeffcient of benzo[c]cinnoline-N-oxide. A mechanism for the electrode reaction is proposed.
A novel concept for the migration of microparticles in an electrolyte solution, electromagnetophoresis (EMP), was demonstrated for the first time using a homogeneous magnetic field applied at right angles to the current in a closed microcell. The direction of the migration of polystyrene latex particles was perpendicular to the magnetic field and to the current, whereas it was reverse to a hypothetical Lorentz force expected for a positive charge in the system. The experimental results showed that the larger were the particles’ diameters, the faster did they migrate in proportion to the second power of the diameter. Moreover, the velocity of the migration was proportional to both the current and the magnetic field. These results proved that the dominant force of the migration was electromagnetic buoyancy.
Monopodal and oligopodal Mg2+-selective ionophores were characterized by their selectivity coefficients (Separate Solution Method, SSM) in plasticized poly(vinyl chloride) (PVC) membranes. Based on a theoretical model published earlier, the stoichiometry of the Mg2+-ligand complexes was estimated while referring to the optimum molar ratio of anionic sites relative to ionophore. The sensitivity of malondiamide substituted azacrown compounds to the varying lipophilicity of the plasticizer, and to the addition of anionic sites was compared with malondiamide derivatives attached to a benzene core. In addition, the lipophilicity of these ligands was determined. In conclusion, the two classes of ionophores were rated concerning their use in human blood and urine specimens.
A simple and rapid procedure is presented for the reliable determination of antimony in steel based on differential pulse anodic stripping voltammetry without any removal of iron matrix. Optimum conditions included a supporting electrolyte of 0.1 mol dm-3 nitric acid-0.1 mol dm-3 sulfuric acid, a pre-electrolysis of -0.5 V vs. the saturated calomel electrode for 300 s at a rotating gold film electrode, and subsequent stripping of the deposit on the electrode surface by a positive going potential scan at a rate of 40 mV s-1. Antimony(V) was chemically reduced to antimony(III) by potassium iodide prior to voltammetric measurements. The interference of iron(III) was eliminated by simultaneously reducing it to iron(II) with the iodide. The generated iodine was reduced with L(+)-ascorbic acid. Arsenic(III), bismuth(III) and copper(II) interfered with the antimony determination severely. The proposed method has been successfully applied to the determination of antimony at the µg g-1 level in steels within 50 min without any troublesome preconcentration steps using harmful chemicals. The detection limit (3σ) with a deposition time of 300 s was 0.19 ng cm-3 (1.6×10-9 mol dm-3).
A new and simple method for detecting and color imaging of L-glutamate released in mouse-brain slices is described based on an enzyme-coupling reaction. The method utilizes L-glutamate oxidase (GluOx) and horseradish peroxidase (HRP) immobilized in a bovine serum albumin (BSA)-glutaraldehyde matrix on a poly-L-lysine-coated glass cover slip. The enzymes are spontaneously and continuously supplied from the membrane into an extracellular solution of the brain slice placed on the membrane after dipping in a redox substrate (DA-64). The Bindschedler’s Green (BG) converted from the DA-64 by the enzyme reaction gives green signals in the brain slice, which are related to the concentration of L-glutamate released in its regions. The first examples of color images for the spatial distribution of L-glutamate in the regions of adult mouse brain slices are demonstrated. The regions where the intense green signals were observed matched the reported distribution of mRNAs encoding the NMDA receptor in the mouse-brain slice.
A specific antibody has been produced for developing immunoaffinity chromatography of optically active bufuralol and its 1′-oxidized metabolites. Spleen cells from a BALB/c mouse, which had been immunized with the (1R)- or (1S)-1′-oxobufuralol O-carboxymethyl oxime-bovine serum albumin conjugate, were fused with P3/NS1/1-Ag4-1 myeloma cells. After screening by enzyme-linked immunosorbent assay (ELISA) using a β-galactosidase-labeled antigen, one for (1R)-bufuralol and three kinds for (1S)-bufuralol of antibody-secreting hybridoma clones were established. The monoclonal antibodies, Ab-R-12 and Ab-S-1,were determined to have favorable characteristics for preparing the immunosorbent, because each of them was specific for (1R)- or (1S)-bufuralols and its corresponding 1′-oxidized metabolites but showed significantly low cross-reactivities with their antipodes including 1′-oxidized metabolites.
A fluorescent chemo-sensor for endocrine-disrupting chemicals has been studied by investigating fluorescence spectral changes with and without a guest molecule of regio-selective bis dansylglycine or anthranilate modified β-and γ-cyclodextrins. These host compounds show an increasing or decreasing pure monomer fluorescence intensity upon the addition of such guests as dioxin analogues, p-nonylphenol, 2,4-dichlorophenoxyacetic acid, bisphenol A, and diethyl phthalate. The extent of the fluorescence variations with the guest is used to display the sensing factors, ΔI/I0, of these host molecules, where I and I0 are the fluorescence intensities in the presence and absence of a guest and ΔI is I-I0. These hosts exhibit various values of ΔI/I0, which indicates the possibility of pattern recognition for endocrine-disrupting chemicals. These guests are detected with a remarkable response range by these hosts.
A high-performance liquid chromatographic method for the direct determination of platelet-produced thromboxane B2 in human serum is described. The method is based on direct derivatization of the thromboxane B2 in human serum with 6,7-dimethoxy-1-methyl-2(1H)-quinoxalinone-3-propionyl carboxylic acid hydrazide. The derivatization reaction proceeds in aqueous solution (or serum sample) in the presence of pyridine and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide at 37°C. The resulting fluorescent derivative of thromboxane B2 is separated by column-switching chromatography using a first column (YMC-Pack C4) for the trap and clean-up of the derivative and a second column (YMC-Pack Ph) for complete separation of the derivative. The derivative is detected spectrofluorometrically at 445 nm with excitation at 367 nm. The detection limit (signal to noise ratio=3) for thromboxane B2 is 10 pmol (3.7 ng)/ml serum. The present method is highly sensitive and simple without any clean-up, such as in conventional liquid-liquid and solid-phase extraction.
A comparison of two multivariate calibration methods, partial least squares (PLS) and principal component regression (PCR), applied to high-performance liquid chromatography (HPLC) data, is presented for the resolution of a pesticide mixture. The data set showed both coeluted peaks and overlapped absorption spectra. Besides, there is an additional overlapping between the signal of the mobile phase and that of some pesticide. Multivariate calibration models were evaluated using different criteria to choose the optimum number of latent variables. It is shown that PLS yields the best predictive models. Furthermore, two methods for selecting regions were applied with the goal to achieve an improved prediction ability in the present multicomponent determination by HPLC-DAD (diode array detector) with PLS. The selection of regions associated with a large correlation to the concentration and with large values in loading-weighs (from PLS) were considered. It is concluded that feature selection can also improve the multivariate calibration results using chromatographic data.
A continuous-precipitation flow injection system coupled on-line with atomic absorption spectrometry for the determination of flavone in bee chrysalis has been developed. A complex precipitate was formed by injecting alkaline lead acetate into bee chrysalis samples and was retained on a Perspex filter followed by elution with nitric acid solution. The extraction method for flavone by the combination of a cold-methanol and alkaline solution was studied. The chemical conditions and the FI parameters were studied in detail. The calibration curve was linear over the range 1 - 100 µg ml-1. The detection limit was 0.6 µg ml-1. The relative standard deviation was 2.8% (n=9, 10 µg ml-1) and the recovery was 95.8 - 104%.
A simple and accurate procedure for simultaneous spectrophotometric and spectrofluorometric determinations of iodate and periodate in aqueous media has been developed. The determination of periodate is based on the selective oxidation of Alizarin Navy Blue to produce a fluorescent compound, that can be found by flow-through spectrofluorometric detection (λex=370 nm, λem=516 nm). On the other hand, periodate and iodate react with iodide to produce iodine, which is determined by spectrophotometric detection at 349 nm. The injected sample was split into two streams, one of which was directly treated with Alizarin Navy Blue and passed to the flow cell of the spectrofluorometer. A fluorescence signal at 516 nm was due to periodate. The other stream was treated with iodide and sulfuric acid and then passed through the flow cell of the spectrophotometer. The increase in absorbance at 349 nm was due to periodate and iodate. The influences of the acid concentration, reagent concentration and manifold variables were studied. The effect of diverse ions on the determination of periodate and iodate by the proposed method was also investigated. Periodate and iodate can be determined in the range of 1.0×10-5 - 2.2×10-4 M and 1.0×10-5 - 2.0×10-4 M, respectively. Within the 3σ detection limit was 3.5×10-6 M for periodate and 1.0×10-6 M for iodate, respectively. Applying this method to the analysis of iodate and periodate in artificial fresh-water samples was successfully carried out.
Selenium(IV) and selenium(VI) in river water were determined differentially by hydride generation inductively coupled plasma atomic emission spectrometry. Selenium(IV) in the water was extracted with 4-nitro-o-phenylenediamine into toluene as 4-nitropiazselenol. The extract was concentrated by evaporation, decomposed with nitric and perchloric acids, and reduced with concentrated hydrochloric acid. The total selenium was determined by digesting the water with nitric, sulfuric and perchloric acids and reducing the selenium with concentrated hydrochloric acid. The interfering transition metals were eliminated by elution with Chelex 100 chelating resin. The siliceous residues deposited during the digestion were dissolved with hydrofluoric acid. The selenium(VI) content was estimated by subtracting the selenium(IV) content from the total selenium. The detection limit (3 times the signal to noise ratio) for both the total selenium and selenium(IV) with 500 ml water samples were 0.03 ng ml-1. The relative standard deviations of the total selenium and selenium(IV) were 4.2 and 17.2%, respectively.
Ultratrace metal impurities (Be, Al, Ti, Cr, Ni, Nb, Mo, Sn, W, Th, and U) in high purity tantalum metal, tantalum(V) oxide, and tantalum pentaethoxide were determined by a combined system of flow injection with an anion exchange column and inductively coupled plasma mass spectrometry (ICP-MS). In the present combined system, the on-line matrix separation and multielement determination of impurity elements could be performed. When 2 M HCl/0.1 M HF mixed solution and 1 M HNO3/0.1 M HF mixed solution were used as the carrier solutions, Be, Al, and Ti for the former, and Cr, Ni, Nb, Mo, Sn, W, Th, and U for the latter were eluted from the column without any tantalum matrix. The detection limits (3σ) of analyte elements were in the range over 0.003 - 0.14 ng/ml as the sample solution basis. The present method was applied to the determination of metal impurities in high purity tantalum materials. The concentrations of Be, Ti, Mo, Sn, Th, and U were at the ng/g level, while those of other elements were in the range over the μg/g - ng/g level.
An analytical method based on the hyphenation of liquid chromatography and inductively coupled plasma mass spectrometry was developed and used for the speciation of antimony in environmental samples. The baseline separation of inorganic Sb(III) and Sb(V) was achieved by using a mobile phase of 2 mmol/l phthalic acid-5 mmol/l EDTA at pH 4.5 on a silica-based anion-exchange column (Synchropak Q300, 100 × 4.6 mm i.d.). The retention times were 164 and 260 s for Sb(V) and Sb(III), respectively. The calibration curves were linear over the range of 1.0 - 100 µg/l for the investigated Sb species. The detection limits were 10 pg and 30 pg per 100 µl sample for Sb(V) and Sb(III), respectively. The precision, evaluated by using the relative standard deviation (RSD) with a 5 µg/l standard solution, was 2.4% and 4.3% (n=6) for Sb(V) and Sb(III), respectively. The detection limits achieved in the present work were sufficiently low to measure Sb species in environmental samples. The proposed method for the speciation of Sb was applied to the determination of Sb(V) and Sb(III) in tap-water and the aqueous extracts of airborne particulate matter. The results showed that for airborne particulate matter there are multiple Sb species.
In this study, a method was developed for preconcentration and determination of palladium in alloys with flame atomic absorption spectrometry (FAAS). For preconcentration, a column containing Amberlite XAD-16 has been used and the preconcentration conditions have been investigated as a function of pH, elution solution, complexing agent, volume of sample solution and flow rate of the sample solution. The effect of some matrix elements, such as Fe, Cu, Ni, Na, K, Ca and Mg, on the recovery of palladium has also been investigated. At optimum conditions determined experimentally, the recovery of palladium was found as to be 98.03±0.08%. For the determination of the adsorption behavior of the resin, the adsorption isotherm of palladium has been studied, The binding equilibrium constant (430 l mol-1) and the adsorption capacity (35.6 mg g-1) have also been calculated. The proposed method has been applied to the standard reference material (SRM) and palladium has been determined with the relative error 5.68%. The detection limit of the analyte has been found to be 0.051 mg l-1.
A long-path-length spectroelectrochemical technique was developed for investigating the EC mechanism and evaluating the kinetic parameters under a semi-infinite condition. The chronoabsorbances were obtained by a digital simulation method. Simulated results showed that the shapes of A-t curves are markedly dependent upon the relative values of the molar absorptivities of spieces A, B and C. When εA=0, εB/ εC≥5 or εC=0, 0≤εA/εB<0.5, the system absorbance passes through a maximum (Amaxt) interestedly. While εB=0, 0.2≤εA/εC≤1, there appears a minimum (Amint). Either Amaxt or Amint is closely related to the chemical reactions following charge transfer. When there is Amaxt at moment tmax in the A-t curve, increasing the value of the first-order rate constant (k1) causes Amaxt and tmax to decrease; while increasing the diffusion coefficient (DB) for species B causes Amaxt to increase, but tmax to decrease. This opposite effect enables us evaluate k1 and DB both simultaneously and precisely. The elctrooxidation of p-aminophenol in an acid aqua solution was experimentally investigated by a long-path-length spectroelectrochemical technique. The pseudo first-order rate constant and the diffusion coefficient for the electrooxidized intermediate quinone imine were successfully evaluated by this method.