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排序方式: 共有1884条查询结果,搜索用时 15 毫秒
81.
Vinod Kumar Gupta Ashok Kumar Singh Sameena Mehtab Barkha Gupta 《Analytica chimica acta》2006,566(1):5-10
A new PVC membrane electrode for Co2+ based on N,N′-bis(salicylidene)-3,4-diaminotoluene, an excellent neutral carrier, has been fabricated using sodium tetraphenylborate (NaTPB) as an anionic excluder and dioctylphthalte (DOP) as a solvent mediator. The electrode exhibits a linear potential response in the concentration range of 7.9 × 10−8 to 1.0 × 10−1 M with a slope of 30 ± 0.2 mV per decade. The detection limit of the proposed sensor is 5.0 × 10−8 M and it can be used over a period of 5 months. The proposed sensor revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals and could be used in the pH range of 2.0-9.0. This electrode was successfully applied for the determination of Co2+in real samples and as an indicator electrode in potentiometric titration of cobalt ions. 相似文献
82.
《Electroanalysis》2004,16(4):268-274
An amperometric method for the determination of the neurotoxic amino acid β‐N‐oxalyl‐L ‐α,β‐diaminopropionic acid (β‐ODAP) using a screen printed carbon electrode (SPCE) is reported. The electrode material was bulk‐modified with manganese dioxide and used as a detector in flow injection analysis (FIA). The enzyme glutamate oxidase (GlOx) was immobilized in a Nafion‐film on the electrode surface. The performance of the biosensor was optimized using glutamate as an analyte. Optimum parameters were found as: operational potential 440 mV (vs. Ag/AgCl), flow rate 0.2 mL min?1, and carrier composition 0.1 mol L?1 phosphate buffer (pH 7.75). The same conditions were used for the determination of β‐ODAP. The signal was linear within the concentration range 53–855 μmol L?1 glutamate and 195–1950 μmol L?1 β‐ODAP. Detection limits (as 3σ value) for both analytes were 9.12 and 111.0 μmol L?1, respectively, with corresponding relative standard deviations of 3.3 and 4.5%. The biosensor retained more than 73% of its activity after 40 days of on‐line use. 相似文献
83.
《Electroanalysis》2003,15(14):1204-1211
Two types of glassy carbon (GC) powder (i.e., Sigradur K and Sigradur G) have been mixed with mineral oil to obtain glassy carbon paste electrodes (GCPE's). The electrochemical behavior of such electrodes at different percentages of glassy carbon has been evaluated with respect to the electrochemistry of ferricyanide as revealed with cyclic voltammetry and the best paste composition was chosen. GC was then modified with Prussian Blue (PB), mixed at different percentages with unmodified GC and with a fixed amount of mineral oil in order to obtain PB modified glassy carbon paste electrodes (PB‐GCPE's). PB‐GCPE's with different percentages of GC modified with PB (PB‐GC) were compared and the dependence on the amount of PB on their performances was evaluated by studying the parameters of cyclic voltammetry (i.e., current peak, ΔEp, anodic and cathodic current ratio, charge density) and the amperometric response to H2O2. Data interpretation based on the GC surface area is presented. GCPE's with a selected amount of PB‐GC were then tested as H2O2 probes and all the analytical parameters together with the dependence on pH were evaluated. Some preliminary experiments with these electrodes assembled as glucose, lysine and lactate biosensors are also reported. 相似文献
84.
Maria Bocheska Maria Hoffmann Urszula Lesiska Emilia Luks Wanda Radecka-Paryzek 《Tetrahedron》2005,61(52):12307-12313
New compounds: 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diisopropoxyphosphorylpropoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-methoxyethoxyphosphorylpropoxy)calix[4]arene (2) were synthesized and their ionophoric properties in ion-selective membrane electrodes were studied in comparison with already described by us 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(3-diethoxyphophorylpropoxy)calix[4]arene (3). Complexes of 1 with calcium(II), lanthanum(III), europium(III) and gadolinium(III) nitrates were prepared in direct reaction of the ligand and appropriate metal salts. They were characterized by spectral data (IR, UV/Vis, luminescence, NMR, ESI-MS) and elemental analysis. The similarity in complexing behavior of the (dialkoxyphosphoryl)propoxy-calix[4]arenes toward calcium and some lanthanides was observed. 相似文献
85.
The kinetics of nonisothermal crystallization and melting of blends of ultra-high molecular weight polyethylene (UHMWPE) and polyethylene high density with normal molecular weight (NMWPE) are investigated by means of differential scanning calorimetry (DSC). Mixing the components at a temperature below the flow temperature of UHMWPE (215 °C) results in increased crystallization/melting rates of the individual components in the blends above the corresponding additive values. The morphological observations of the blends, carried out by means of polarization microscopy, show that a strong boundary of both types of structures (UHMWPE non-flowing aggregates and NMWPE spherulite structures) does not exist. The NMWPE spherulites' dimensions decrease on increasing the UHMWPE concentration in the blends, but their number increases. The facilitation of the crystallization/melting of the components in the blends is explained in terms of mutual influence exhibited by the components with respect to each other. It is due to the inner stresses in nonflowing UHMWPE characterized with a lot of entangled tie molecules and to the partial co-crystallization of NMWPE molecules with the flowing part of UHMWPE. At mixing temperatures above 215 °C the melting/crystallization integral kinetic curves have only one linear part in contrast to these of the same blend (11 ratio of components), prepared at 190 °C. The rates of melting/crystallization remain almost constant with the increase of the mixing temperatures. 相似文献
86.
87.
A photocurable acrylate matrix nitrate-sensitive membrane containing 2-nitrophenyl n-octyl ether as mediator and tetraalkylammonium nitrate as an active compound is described. The photocuring was achieved by the use of photoinitiators containing diaryliodonium chloride. This acrylate membrane is patternable via a photolithographic process with a only slight loss of electrochemical characteristics. 相似文献
88.
Present proteomics and biomedicine require sensitive analytical methods for all proteins. Recent progress in electrochemical analysis of peptides and proteins based on their intrinsic electroactivity is reviewed. Tyrosine and/or tryptophan‐containing proteins are oxidizable at carbon electrodes. At mercury electrodes all peptides and proteins (about 13 peptides and >25 proteins were tested) produce chronopotentiometric peak H at nanomolar concentrations. This peak is sensitive to changes in protein structure. Microliter sample volumes are sufficient for the analysis. Electrochemical methods can be used in studies of nucleic acid‐protein interactions and can be applied in biomedicine. Examples of such applications in neurogenerative diseases and cancer are presented. 相似文献
89.
《Electroanalysis》2003,15(11):961-968
The electrochemically initiated reaction of p‐phenylenediamines with sulfide in aqueous media is well documented. We now report the adaptation of this chemistry into nonaqueous media. This is critically appraised as a means of detecting sulfide. The electrochemically initiated reaction of N,N‐diethyl‐p‐phenylenediamine with sulfide is shown at both macro‐ and platinum microdisk electrodes with quantitative detection of sulfide produced by means of the enhanced currents observed upon its addition. The linear detection range for sulfide is dependent on the concentration of N,N‐diethyl‐p‐phenylenediamine present with a linear range from 28–3290 μM and a limit of detection of 22 μM achievable. This represents a large increase compared to that found previously in aqueous media and offers the prospect of more ready applications in high temperature systems. 相似文献
90.
《Electroanalysis》2005,17(20):1865-1869
A novel anion‐selective PVC membrane electrode based on bis‐[(3‐ferrocenyl)‐(2‐crotonic acid)] copper(II) complex [Cu(II)‐BFCA] as neutral carrier is described, which demonstrates excellent potentiometric response characteristics toward thiocyanate ion and anti‐Hofmeister selectivity sequence in following order: SCN?>I?>ClO >Sal?>Br?>NO >Cl?≈NO >SO >SO . The electrode shows a near‐Nernstian response for thiocyanate ion in a wide range of 9.0×10?7–1.0×10?1 M with a detection limit 6.8×10?7 M and a slope of ?59.1 mV/decade in pH 5.0 of phosphate buffer solution at 20 °C. The influences of lipophilic cationic and anionic additives on the response properties of the electrode were investigated. High sensitivity and wide linear dynamic range were observed for the electrode in the presence of hexadecyltrimethylammoniumborate (HTAB) as a lipophilic cationic additive. The electrode was successfully applied to the determination of thiocyanate ion in waste water and human saliva. 相似文献