Adsorptive stripping voltammetric determination of 1-(4′-bromophenyl)-3,3-dimethyltriazene

The optimum conditions were established for the determination of the genotoxic substance 1-(4-bromophenyl)-3,3-dimethyltriazene by differential-pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 × 10^–4 to 1 × 10^–7 mol dm^–3. The sensitivity of the determination can be improved through adsorptive accumulation of the investigated substance on the surface of the hanging mercury drop electrode: differential pulse adsorptive stripping voltammetry can be used in the concentration range 1 × 10^–7 to 2 × 10^–10 mol dm^–3. The relative standard deviation (for ten determinations at 2 × 10^–10 mol dm^–3) was 7.5%.     

A novel catalytic adsorptive stripping voltammetric method for the determination of germanium ultratraces in the presence of chloranilic acid and the V(IV)·HEDTA complex

A novel, sensitive catalytic adsorptive stripping voltammetric procedure which can be used to determine trace amounts of germanium is described. The method is based on the interfacial accumulation of the complex formed by Ge(IV) and the product of the reduction of chloranilic acid on the hanging mercury drop electrode or the renewable silver amalgam film electrode, and its subsequent reduction from the adsorbed state followed by the catalytic action of the V(IV)·HEDTA complex. The presence of V(IV)·HEDTA greatly enhances the adsorptive stripping response of Ge. The reduction of the Ge(IV) in the presence of chloranilic acid and V(IV)·HEDTA was investigated in detail and the effects of pH, electrolyte composition, and instrumental parameters were studied. Under optimal conditions, the catalytic peak current of germanium exhibited good linearity for Ge(IV) concentrations in the range of 0.75–60 nM (for 60 s of accumulation at −0.1 V, r² = 0.995) and a low limit of detection (LOD = 0.085 nM). The procedure was successfully applied to determine Ge in water samples.

     

Voltammetric determination of α-tocopherol in the presence of surfactants

As established, α-tocopherol is electrochemically active on glassy carbon electrode in the available range of anodic potentials in acetonitrile and its aqueous mixtures. However, an increase in the water percentage up to 50% and beyond leads to a substantial decrease and then the total disappearance of the analytical signal. A scheme of electrode reaction responsible for the signal formation is proposed. The effect of surfactants on the oxidation of α-tocopherol in aqueous acetonitrile is estimated. As found, surfactants (N-dodecylpyridinium bromide, Triton X-100 and N-cetylpyridinium bromide) enhance the current of α-tocopherol oxidation. The surfactants reduce the detection limit and extend the analytical range. Analytical methods for the voltammetric quantification of α-tocopherol in drugs in the presence of surfactants are elaborated and may be recommended for the control of pharmaceuticals.     

Copper–mercury film electrode for cathodic stripping voltammetric determination of Se(IV)

The copper-mercury film electrode has been suggested for the determination of Se(IV) in a wide range of concentration from 1x10(-9) to 1x10(-6) mol L(-1)by square-wave cathodic stripping voltammetry. Insufficient reproducibility and sensitivity of the mercury film electrode have been overcome by using copper(II) ions during the plating procedure. Copper(II) has been found to be reduced and form a reproducible copper-mercury film on a glassy carbon electrode surface. The plating potential and time, the concentration of copper(II) and the concentration of the supporting electrolyte have been optimised. Microscopy has been used for a study of the morphology of the copper-mercury film. It has been found that it is the same as for the mercury one. The preconcentration step consists in electrodeposition of copper selenide on the copper-mercury film. The relative standard deviation is 4.3% for 1x10(-6) mol L(-1) of Se(IV). The limit of detection is 8x10(-10) mol L(-1) for 5 min of accumulation.     

Spectrofluorimetric study and determination of desipramine in the presence of β-cyclodextrin

The native fluorescence intensity of desipramine was enhanced in the presence of β-cyclodextrin in aqueous solution. The inclusion complex formation between these compounds was studied by spectrofluorimetry. A stable complex with a 2: 1 stoichiometry of β-cyclodextrin to desipramine was formed (logβ₂ = 9.29 ± 0.01). In the presence of an optimum concentration of β-cyclodextrin, the fluorescence intensity was linearly proportional to desipramine concentration in the range of 0.1–100 μg/mL (7.2 × 10^?7?1.0 × 10^?4 M) with a limit of detection of 7 × 10^?8 M. The method was successfully applied to the detection of desipramine in its tablets.     

Adsorptive stripping voltammetric analysis of 2,4,6-tri(2′pyridyl)-1,3,5-triazine at a mercury electrode

The redox behaviour of adsorbed species of 2,4,6-tri(2-pyridyl)-1,3-5-triazine (TPTZ) at the surface of a mercury electrode was examined using cycling voltammetry. Based on the adsorption and accumulation of TPTZ at the charged mercury surface cathodic adsorptive stripping voltammetry (CSV) is applied for the trace determination of TPTZ using a differential pulse (DP) technique. Experimental and operational parameters for the quantitative analysis of TPTZ are optimized and the detection limit was found to be 3×10^–9 mol/l. The effect of some interferences, e.g. organic compounds, cations and anions, are investigated.     

Novel and efficient supramolecular synthesis of pyrroles in the presence of β-cyclodextrin in water

A simple and efficient synthesis of highly substituted pyrroles was achieved in water medium via multi-component strategy, using amine,DMAD/DEAD as well as phenacyl bromide catalyzed by β-CD.Utilizing this protocol various pyrrole derivatives were synthesized in good to excellent yields.     

Cathodic stripping voltammetric determination of β-cyfluthrin,a pyrethroid insecticide,using polished silver solid amalgam electrode

Journal of Solid State Electrochemistry - This work describes an electroanalytical procedure for determination of beta-cyfluthrin (βCF), a pyrethroid insecticide, using polished silver solid...     

3,3′,5,5′-Tetramethylbenzidme for the colorimetric determination of manganese in water

Manganese can be determined by colorimetry with previous oxidation of Mn(II) in a strong basic medium, using 3,3,5,5-tetramethylbenzidine as a chromogenic reagent. The molar absorptivity of the reaction product is 3.4 × 10⁴ mol^–1l cm^–1l, the detection limit 3 ng/ml, the RSD (0.5 mg/l,n = 8) 0.9% and the calibration range (1-cm cells) 0.02–0.8 mg/1 V(V), Cr(VI) and Co(II) are the most significant interferences. The new method was compared with an AAS procedure (air-acetylene flame) with previous solvent extraction and also with a colorimetric method for the determination of manganese in sea and drinking water.     

Spline wavelet in the resolution of overlapping voltammetric peaks

Spline wavelet transform is used to resolve overlapping voltammetric peaks. A suitable resolving factor is chosen to multiply the filters of spline wavelet and make it a peak resoluter. Simulated overlapping voltammetric peaks are processed by the peak resoluter and satisfactory results are obtained. Base-line separation can be achieved, the relative errors of peak position are less than 3.0%, and the relative errors of peak area are less than 5.0%. The effect of different resolving factors and spline wavelet basis are discussed. To test the procedure, two systems, cadmium (Ⅱ)-indium (Ⅲ) and lead (Ⅱ)-thallium (Ⅰ), are used.     

Spontaneous and diastereoselective aldol reactions of cyclic β-amino ketones in the presence of water

Direct aldol reactions of 4-methyl-1-piperidone, tropinone and granatanone (pseudopelletierine) take place spontaneously in the presence of water without any catalyst or additional reagents. The anti/syn-diastereoselectivity of the aqueous aldol reaction depends on the amount of water used. The syn-selectivity of the reaction is probably due to the thermodynamic control. Excellent atom economy and low E factors together with anti-selectivity as high as 98:2 for the tropinone aldol were obtained.     

Silver electrodeposition from water–acetonitrile mixed solvents in the presence of tetrabutylammonium perchlorate

In this paper, surface-enhanced Raman spectroscopy has been used to investigate the electrode/electrolyte interface during Ag electrodeposition from water–acetonitrile mixed solvents. The reactivity of acetonitrile during Ag electrodeposition has been monitored, promoted by the electrocatalytic activity of silver clusters electrodeposited onto the electrode surface. The effect of the addition of tetrabutylammonium cations to the mixed solvents has been investigated and its adsorption and tilting on the silver surface has been followed as a function of the cathodic overpotential.     

Liquid—liquid equilibria in water—aliphatic alcohol systems in the presence of sodium chloride

Liquid—liquid equilibria in mixtures of water, propyl or butyl alcohol isomers and sodium chloride have been studied experimentally at 25 °C The solvent behaviour of the various alcohols is discussed. Setschenow constants, calculated from the measured data, are compared with the results of the scaled particle theory.     

Direct synthesis of carbonyl compounds from THP ethers with IBX in the presence of β-cyclodextrin in water

Water, an environmentally friendly reaction medium, has been utilized for the oxidative deprotection of tetrahydropyranyl ethers 1 with IBX at room temperature in the presence of β-cyclodextrin to give the corresponding carbonyl compounds 2.     

A validated method for the determination of traces of UV filters in fish using LC–MS/MS

An analytical method for the determination of UV filter substances in fish tissue has been developed and validated using benzophenone-3, 3-(4-methylbenzylidene)-camphor, 2-ethylhexyl-2-cyano-3,3-diphenyl-2-propenoate and 2-ethylhexyl 3-(methoxyphenyl)-2-propenoate as target analytes. The fish fillets were homogenised and extracted by Soxhlet extraction. The extracts were run through a clean-up process including gel permeation chromatography followed by solid-phase extraction. Quantification of the compounds was performed using liquid chromatography with tandem mass spectrometric detection. Blank fish as well as spiked blank fish were analysed to validate the analytical method. The analytical method developed has the multiple advantages of enabling separation, simultaneous identification and quantification of each of the four selected compounds in a single run. Contamination of blank samples and abnormally high concentrations in spiked samples were avoided by taking extensive precautions during the fish preparation procedure. The method was validated in accordance with internationally accepted criteria, such as specificity, accuracy and repeatability. The combination of LC with tandem mass spectrometry ensures a high level of specificity. The accuracy of the method was reported as the mean recovery rate for the analytes in the sample matrix. Mean recoveries were in the range 86–108%. The precision is expressed as the relative standard deviation, and in all but one of the cases was 20% or below. The accuracy of the method allows residue analyses to be performed on biological matrices at ng/g levels. The determined limit of quantification for each analyte was 8 ng/g fish. For all spiking levels ≥8 ng/g, relative standard deviations were ≤ 20%.     

Frequency characteristic of series piezoelectric sensor and application to the determination of water in organic solvents

Theoretical consideration was proposed for the frequency response of a series piezoelectric sensor to the properties of liquid and verified experimentally. This kind of sensor has sensitive and selective frequency response to the permittivity and specific conductivity of solution with excellent stability, and was applied to the determination of micro-content of water in organic solvents. The detection limit is 0.01 g/L in dioxane.     

A new determination of the structure of water at 25°C

The results of a new neutron diffraction experiment to measure the structure of water are presented. The data, measured at the McMaster Nuclear Reactor, are of a high quality and are analysed to yield the hydrogen-hydrogen pair correlation function using a subtraction procedure which has been used in previous experiments of this kind. This procedure circumvents the necessity of applying inelasticity corrections. The results are in good agreement with earlier work and serve to establish the general correctness of the subtraction procedure when used to determine hydrogen correlations. The data are further analysed to yield separate oxygen-hydrogen and oxygen-oxygen partial structure factors for liquid water. For the second part of the analysis an effective mass model of the dynamic scattering law is used, with the model parameter, the effective mass of the scattering particle, chosen by a least-squares fit to the measured differential cross sections. The final pair correlation functions are obtained using a maximum entropy analysis of the structure functions.     

Synthesis of (−)-okundoperoxide and determination of the absolute configuration of natural (+)-okundoperoxide

The first enantioselective synthesis of (3S,4aR,8aR)-1 (the enantiomer of natural okundoperoxide) has been accomplished. The synthesis features: 1) stereoselective installation of the peroxy functionality (16 → 17); 2) ring opening of peroxyacetal and subsequent intramolecular reaction between the hydroperoxide and the vinyl epoxide to form the peroxy six-membered ring (5 → 1). The absolute configuration of okundoperoxide was determined to be 3R,4aS,8aS by comparing specific rotations of the synthetic sample and the natural product.     

Stereoselective synthesis of 2,6-dideoxy-α-l-arabino-hexopyranoside of glycyrrhetic acid in the presence of iodine-containing promoters

Glycosylation of methyl glycyrrhetate withl-rhamnal acetate in the presence of iodine-containing promoters and subsequent hydrogenolysis yield 2,6-dideoxy--l-arabino-hexopyranoside of glycyrrhetic acid, an analog of glycyrrhizic acid, the natural glycoside of licorice root extract.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2993–2996, December, 1996.