A three-phase electrode consisting of a droplet of a nitrobenzene solution of iron(III) tetraphenyl porphyrine chloride (Fe(III)-TPP-Cl) attached to a graphite electrode and immersed in an aqueous electrolyte solution was applied to determine the standard Gibbs energies of transfer of cations between water and nitrobenzene. The reduction of Fe(III)-TPP-Cl prompts the transfer of the cations from the aqueous to the organic phase. The system is chemically and electrochemically reversible. 相似文献
A new electrochemical method for the determination of trace water in methanol has been developed. This method is based on the effect, that a minor change in the water content affects the value of conductivity measured for dissolved in the solutions electrolyte. The conductivity measurements were performed for four inorganic salts, i.e. NaCl, KCl, RbCl, and CsCl in solutions with different amounts of water traces in methanol and the calibration curves for three of them were determined. With the exception of cesium chloride the high values of correlation coefficients for the regression lines as well as low limits of detection were achieved in all cases which indicates that this method is a useful tool for the determination of the trace amounts of water in methanol. 相似文献
A rapid electroanalytical method for the determination of residual styrene in polystyrene is described. The sample of polymer was dissolved in toluene and, following the addition of 10% DMF and electrolyte, a square-wave voltammogram was recorded at a gold microdisc electrode (radius, 6 mum). A standard addition technique was used to relate the peak current to the styrene concentration in solution and, hence, the styrene content of the polymer. The method gave results which are similar to those of the accepted standard procedure. It does not, however, require the precipitation of the polymer and hence is quicker and more convenient. 相似文献
A method for calculating the Gibbs energy of nonspecific solvation of nonelectrolytes was suggested. The new equation for the Gibbs energy of nonspecific solvation contains one solvent parameter that characterize nonspecific solvent-solute interactions and two experimental Gibbs energies of solvation in two standard solvents. The method is applicable to a wide range of solutes and solvents. It was successfully used to describe some 800 Gibbs energies of solvation for systems without specific solvent-solute interactions. 相似文献
A method has been developed for the determination of traces of silver in the presence of large concentrations of interfering metals, particularly copper, involving reduction of the silver on a glassy-carbon electrode modified by an adsorbed layer of previously deposited hydrogen. 相似文献
A new rapid method has been developed for the determination of Th, Pu, Np, U, Am and Cm isotopes in water samples of about 1 L. Actinides are pre-concentrated by co-precipitation with Ca phosphate, sequentially separated on stacked TEVA and TK221 cartridges and measured by alpha spectrometry. The TK221 extraction chromatographic resin contains i.e. CMPO and DGA extractants. It has been characterized by measuring the weight distribution ratios (Dw) of actinides which are higher than 1000 for all actinides in 3 M HNO3. The method has been optimized, applied for the analysis of tap and seawater samples and validated by participating in an IAEA proficiency test. Chemical recoveries for all actinides are better than 50%. The method can be performed within one day.
An entirely automated system for low level Kjeldahl nitrogen determination in water samples is described. Samples are continuously digested at 300 °C with sulfuric acid and hydrogen peroxide to convert the organic nitrogen to ammonia, which is determined colorimetrically with sodium salicylate and sodium dichloroisocyanurate (as chlorine source). The method has a range of 10–500 μg Nl-1 with good precision and accuracy. 相似文献
Irradiation and post-irradiation losses in 7 crude oils encapsulated in polyethylene and irradiated in a flux of 1012n·cm−2 sec−1 have been thoroughly studied. The fraction of mercury released during irradiations ranging from 10 minutes to 2 hours is
proportional to the integrated flux received by the samples and does not differ substantially from one oil to another. Post-irradiation
loss rates at 20°C range between 0.017 and 0.027%·hr−1. Storage at−20°C reduces them by at least a factor of 2. The influence on the activity of197Hg due to losses in sample weight occuring during the post-irradiation period has been examined. The fraction of radiomercury
retained inside the walls of the irradiation vials versus the irradiation time has been assessed. Contamination of an inner
irradiation site following prolonged irradiations of oils containing 150 μg/g of this element has been evaluated and found
to have a negligible impact for trace measurements above the ng/g level. 相似文献
In pH 5.5, 0.1 mol l−1 HAc-NaAc buffer solution, trinitrophenol has been determined quantitatively with differential pulse voltammetry by detecting
its reduction peak currents at the glassy carbon electrode. The detection sensitivity was enhanced significantly by the addition
of the surfactant of cetyl pyridinium chloride, and the enhancement mechanism was also studied in detail. The linear calibration
range was 8.0 × 10−7 to 2.0 × 10−4 mol l−1, and the detection limit was established to be 1.9 × 10−7 mol l−1. This method has been applied to the determination of trinitrophenol in water sample, and the recovery was from 97.6 to 103.5%. 相似文献
The capacity to transfer protons between surface groups is an innate property of many proteins. The transfer of a proton between donor and acceptor, located as far as 6-7 A apart, necessitates the participation of water molecules in the process. In a previous study we investigated the mechanism of proton transfer (PT) between bulk exposed sites, a few ?ngstr?ms apart, using as a model the proton exchange between the proton-binding sites of the fluorescein molecule in dilute aqueous solution.1 The present study expands the understanding of PT reactions between adjacent sites exposed to water through the calculation the minimum energy pathways (MEPs) by the conjugate peak refinement algorithm2 and a quantum-mechanical potential. The PT reaction trajectories were calculated for the fluorescein system with an increasing number of water molecules. The MEP calculations reveal that the transition state is highly strained and involves a supramolecular structure in which fluorescein and the interconnecting water molecules are covalently bonded together and the protons are shared between neighboring oxygens. These findings are in accord with the high activation energy, as measured for the reaction, and indicate that PT reactions on the surface proceed by a semi- or fully concerted rather than stepwise mechanism. A similar mechanism is assumed to be operative on the surface of proteins and renders water-mediated PT reactions as highly efficient as they are. 相似文献
A simple enzymatic method is described for field TLC detection and determination of fenitrothion as fenitrooxon in water, with pig liver acetone powder as enzyme source. By this method, fenitrothion can be detected as fenitrooxon at ng levels and amounts ranging from 5 to 50 ng can be estimated. 相似文献
Coefficients of the interphase distribution of nicotinic acid are determined in aqueous solution systems of ethanol-hexane and DMSO-hexane at 25.0 ± 0.1°C. They are used to calculate the Gibbs energy of the transfer of nicotinic acid from water into aqueous solutions of ethanol and dimethylsulfoxide. The Gibbs energy values for the transfer of the molecular and zwitterionic forms of nicotinic acid are obtained by means of UV spectroscopy. The diametrically opposite effect of the composition of binary solvents on the transfer of the molecular and zwitterionic forms of nicotinic acid is noted. 相似文献
Gibbs energies for the transfer of glycylglycine and glycylglycinate ions from water to water-dimethylsulfoxide solvents are determined from the interface distribution of substances between immiscible phases in the composition range of 0.00 to 0.20 molar fractions of DMSO at 298.15 K. It is shown that with a rise in the concentration of nonaqueous components in solution, we observe the solvation of dipeptide and its anion, due mainly to the destabilization of the carboxyl group. 相似文献
This paper describes an electrochemical biosensor for free cholesterol monitoring. The sensor is a multienzymatic electrodic system in which horseradish peroxidase and cholesterol oxidase are simultaneously immobilized within a polymeric film, on the surface of a pyrolitic graphite electrode. From voltammetric and amperometric (flow-injection) data obtained, the efficiency, reproducibility and stability of the system are discussed. Results obtained, of interest for basic and applied biochemistry, represent a first step for construction of a mediator-free biosensor with potentialities for a successful application in the biosensor area. 相似文献