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21.
Using voltammetric, galvanostatic and potentiostatic techniques, the electrodeposition of cuprous thiocyanate on a copper amalgam electrode has been studied in acidic solutions containing various thiocyanate ion concentrations. Under the conditions used, the formation of two successive monolayers of CuSCN could be studied before the onset of bulk deposition. It was found that the formation of the first monolayer proceeds according to a complex adsorption-nucleation and growth mechanism. In the first stage, cuprous thiocyanate is adsorbed on the amalgam electrode; in the second, the disordered layer of adsorbate rearranges to form two-dimensional crystalline centres; and in the third stage, these centres grow, completing the formation of the entire monolayer. The second monolayer is formed in a much simpler way, according to a mechanism of two-dimensional, instantaneous nucleation and growth. At high thiocyanate ion concentration, the formation of the CuSCN layer is obscurred by the extensive formation of solution soluble species. 相似文献
22.
Renata Wietecha Paweł Kościelniak Teresa Lech Tomasz Kielar 《Mikrochimica acta》2005,149(1-2):137-144
This study describes a simple, rapid and reliable method for simultaneous determination of selenium and arsenic in human hair by means of atomic fluorescence spectrometry combined with a hydride generation technique (HG-AFS). The procedure developed encompasses microwave digestion of a sample in the nitric acid environment only. The interferences caused by nitrous oxides are eliminated by removing a gas from above the digested solution with a stream of argon. The sample is then chemically treated in a flow-through hydride generation system and exposed to measurements in a double-channel atomic fluorescence spectrometer. The method permits determining both analytes in the linear range of 0.5–100µgL–1 with a detection limit equal to 0.2µgL–1, as well as with very good repeatability not exceeding 1% for Se and 2% for As. No mutual interferences from either of the analytes in the concentrations ranges matching the hair composition were found. The method was verified in terms of accuracy with the use of a reference material and then applied to the analysis of the natural samples of human hair. 相似文献
23.
Elzbieta Muszalska Renata Bilewicz Elzbieta Luboch Anna Skwierawska Jan F. Biernat 《Journal of inclusion phenomena and macrocyclic chemistry》1996,26(1-3):47-59
Two methods are described for preparing monomolecular layers of crown ethers with an azo or azoxy group in the macrocycle. When the molecules used to build the monolayer are soluble in aqueous solutions, adsorptive preconcentration on mercury electrodes was used to prepare the monolayer coating. The monolayer was electroactive due to the presence of the azo or azoxy unit in the molecules. Monolayers of crown ethers bearing an azo group in the macrocycle were shown to recognize alkali metal cations present in the solution. Changes of the parameters of the voltammetric reduction peaks - peak potential and peak width, served as an indication of specific interactions of the monolayer of 13-membered and 16-membered azocrown ethers with Na+ and K+ cations, respectively.The monolayers capable of recognizing cations have also been prepared on the aqueous solution-air interface, using the Langmuir technique. In this approach, amphiphilic derivatives of the azocrowns were synthesized and the monolayer has been assembled on the subphase containing metal cations. Binding of the cation by the macrocycle has a stabilizing effect on the monolayer and higher collapse pressures are achieved than on the pure water subphase. The monolayer was transferred from the air-water interface on the solid substrate using the Langmuir-Blodgett technique. Thin mercury film electrodes on the Ag substrate, or An films evaporated on glass slides were employed as the electrode substrates. The former gave monolayer modified electrodes of higher stability.Presented at the Sixth International Seminar on Inclusion Compounds, Istanbul, Turkey, 27–31 August, 1995. 相似文献
24.
Estrela Rde C Salvadori MC Raices RS Suarez-Kurtz G 《Journal of mass spectrometry : JMS》2003,38(4):378-385
A method based on solid-phase extraction coupled to liquid chromatography with positive ion electrospray ionization and tandem mass spectrometric detection was developed for the determination of didanosine in human serum, using lamivudine as internal standard. The acquisition was performed in the multiple reaction monitoring mode, monitoring the transitions m/z 237 --> 136.7 for didanosine and m/z 230 --> 111.7 for lamivudine. The method was linear over the range studied (10-1500 ng ml(-1)), with r(2) > 0.98, and the run time was 5 min. The intra- and inter-assay precisions were < or =10% and the intra- and inter-assay accuracies were >95%. The absolute recoveries were 99.8% (10 ng ml(-1)), 98.4% (30 ng ml(-1)), 91.5% (700 ng ml(-1)) and 94.7% (1200 ng ml(-1)). The limits of detection and quantitation were 5 and 10 ng ml(-1), respectively. The method was applied to a bioequivalence study, in which 24 healthy adult volunteers (12 men) received single oral doses (200 mg) of reference and test didanosine formulations (buffered powder for oral solutions), in an open, two-way, randomized, crossover protocol. The 90% confidence interval of the individual ratios (test formulation/reference formulation) for C(max) (peak serum concentration) and AUC(0-inf) (area under the serum concentration versus time curve from time zero to infinity) were within the range 80-125%, which supports the conclusion that the two formulations are bioequivalent regarding the rate and extent of didanosine absorption. 相似文献
25.
Paleari R Ceriotti F Azzario F Maccioni L Galanello R Mosca A 《Bioelectrochemistry (Amsterdam, Netherlands)》2004,62(2):175-179
An immunologically mediated pathway has been largely accepted to be one of the mechanisms involved in the clearance of senescent or prematurely damaged RBC. According to this pathway, RBC removal is mediated by binding of naturally occurring IgG to clustered integral membrane proteins, followed by complement deposition. The validation of an immunoenzymatic method for the detection of RBC-bound autologous IgG is presented. The use of RBC-bound IgG as an index related to red cell age was evaluated by measuring IgG binding in RBC treated with the clustering agent ZnCl2, in density fractionated RBC and in a selected group of patients expected to have an altered RBC life span. The immunoenzymatic method for IgG detection resulted to be reproducible (CV = 3.4%). IgG binding to in vitro clustered RBC was found to be enhanced to a very great extent, about 20 times higher with respect to untreated RBC. A slight but significant increase (about 1.8-fold) in membrane-bound IgG was observed in the highest density fraction of normal RBC, which constituted 1% of the total cells. A significantly greater number of RBC-bound IgG was measured in splenectomized beta-thalassemia intermedia patients and in subjects with secondary decreases in the C3 complement fraction concentration. 相似文献
26.
This paper describes the synthesis of a bicyclic beta-amino acid scaffold in both pure enantiomeric forms and its application as chiral auxiliary in an intramolecular version of the Ugi multicomponent reaction (U-5C-4CR) to prepare alpha-amino acid derivatives of both D- and L-series in a straightforward and very stereoselective manner. The mild conditions required for the Ugi condensation and for the removal of the chiral auxiliary make this method very attractive to prepare a wide range of differently structured N-alkylated and unalkylated amino acid derivatives. 相似文献
27.
α-acyloxyaminoamides can be prepared, with yields ranging from fair to very good (up to 89%), through an Ugi four component reaction by mixing a carbonyl component, a carboxylic acid, an isocyanide and an N-alkylated hydroxylamine in methanol. Preformed nitrones furnish the same final compounds with comparable yields. 相似文献
28.
Both cis- and trans-N-benzyl-azetidine-2,4-dimethanols5 and 6 were prepared and submitted to acetylation in organic solvents catalyzed by lipases. Asymmetrization of diol 5 gave ohe corresponding monoacetate 7, while double sequential kinetic resolution of reacemic 6 gave optically enriched diol 6b and its enantiomer as the corresponding diacetate 10a. Optimized reaction conditions furnished 7, 6b and 10a with e.e. > 99%. 相似文献
29.
Anna Rakowska Robert Filipek Krzysztof Sikorski Marek Danielewski Renata Bachorczyk 《Mikrochimica acta》2004,145(1-4):183-186
The interdiffusion process in thin and thick (500nm–60µm) Au–Ni layers deposited on different substrates is studied using the EDS technique. In-depth X-ray analysis based on the Pouchou and Pichoir method is applied for obtaining the concentration profiles in nanometre scale multi-layers. A theoretical analysis using the Darken method is employed for modelling interdiffusion in the Au–Ni system. Computer simulations, where intrinsic diffusivities of the Au and Ni are functions of composition, are presented and compared with experimental results. 相似文献
30.
Jose′ L. F. C. Lima Antoacutenio O. S. S. Rangel M. Renata S. Souto 《Fresenius' Journal of Analytical Chemistry》1997,358(5):657-662
A flow injection system was developed for the sequential determination of total nitrogen and phosphorus in digests of vegetables
using potentiometric and spectrophotometric detection systems, respectively. A tubular ammonium selective electrode with a
sensor system composed of nonactin/monactin in tris(2-ethylhexyl) phosphate was used. The selectivity limitations of this
electrode were overcome by the inclusion of a gas-diffusion unit in the system that separated ammonium from the rest of the
sample matrix and allowed the determination of total nitrogen and phosphorus by the partition of the sample plug between two
streams.
The results obtained with the developed FIA system were in good agreement with those of the reference methods. Sampling rates
from 40 to 60 samples per hour and relative standard deviations below 3.5% were achieved.
Received: 17 October 1996/Revised: 21 November 1996/Accepted: 27 November 1996 相似文献