摘要:

AbstractThe use of calix[n]arenes as recognition reagents in electroanalysis is reviewed. Calix[n]arenes (n= 4 to 14) are macrocylic phenol‐formaldehyde condensates which may be derivatized at the phenolic oxygen position to produce macrocycles capable of the selective binding of metal cations. Calix[4]arene derivatives having ester, ketone and amide functionality generally exhibit sodium selectivity and the larger calix[6]arenes show a preference for cesium ions. A number of calixarenes have been successfully incorporated into polymeric membrane ion‐selective electrodes (including ISFETs). Calixarene‐based sodium selective ISEs exhibit excellent sensitivity and selectivity, especially over potassium ions, which has allowed usage of these ISEs in assays of sodium in blood and serum. Calixarene‐based ISEs sensitive to potassium, cesium and organic amine ions have also been reported. More recently ISEs and ISFETs sensitive to heavy metal ions such as silver, lead and copper(II) have been fabricated from various sulfur functional group derivatized calix[4]arenes. Potentiometric analytical uses of calixarenes have received most interest to date. However, voltammetric investigations have shown that carbon paste modified electrodes may be prepared with polymeric calixarenes and allow stripping voltammetric determination of lead, copper and mercury simultaneously. Voltammetric studies of calixquinone/hydroquinone and calixarene inclusion complexes have also been reported. Prospects for the future development of calixarenes as ionophoric reagents in electroanalysis are di

ISSN:1040-0397    

DOI:10.1002/elan.1140070302

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractReduced nicotinamide adenine dinucleotide (NADH), produced from glucose‐6‐phosphate dehydrogenase (G6PDH) was catalytically oxidized using diaphorase and 1, 4‐benzoquinone to yield 1, 4‐hydroquinone. This benzoquinone redox mediator was readily detected at an electrode polarized at +0.5 V (vs. Ag/AgCl) so avoiding the high overpotentials required for a direct electrochemical measurement of NADH. Also, the lipophilic nature of the hydroquinone enabled a novel high selectivity plasticized PVC membrane mounted over the electrode to be exploited. The mediator/PVC combination achieved NADH calibration linear up to at least 100 μM. When used to assay G6PDH activity, a linear calibration from 0.1–1.0 U/mL was produced. The detection system offers the possibility of highly selective measurement of dehydrogenase enzyme activity in biological samples without sample preparation and could provide the basis for simplified homogeneous immunoassays as well as dehydrogenase amperometric enzyme

ISSN:1040-0397    

DOI:10.1002/elan.1140070303

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe fluoride ion‐selective electrode has been used in continuous flow analysis to determine the fluoride concentration in aqueous solution. The varying electrode potentials,E(t), were collected in the first 60 s by an interfacing computer, and the equilibrium potential of the electrode was predicted using an extrapolation method. This value agrees to within ±0.5 mV of the comparative value obtained by allowing sufficient time for the electrode to reach a steady state. Like flow‐injection (FI), continuous flow (CF) analysis with this extrapolation method significantly shortens the time required for routine fluoride concentration measurements, but it also achieves a higher sensitivity than FI. The method has been applied to the determination of fluoride in city tap w

ISSN:1040-0397    

DOI:10.1002/elan.1140070304

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractAmperometric detection using the batch injection analysis technique has been studied and compared with the current obtained at the wall‐jet electrode under similar conditions using the oxidation of potassium ferrocyanide and the injection of samples of volume 10 to 100μL. The form of the current transients has been analyzed and compared with the steady‐state response at wall‐jet disk electrodes. Good agreement is found at high dispension rate, differences at lower dispension rates being ascribed to radial diffusion effects. The importance of tip–electrode distance and injection volume have been evaluated; it is shown that the optimum distance is 3 mm and that maximum sensitivity requires a minimum injection volume of 14 μL. A detection limit of 50 μM using simple amperometric detection is estimated. Implications of these results for the efficient application of amperometric batch injection analysis are

ISSN:1040-0397    

DOI:10.1002/elan.1140070305

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe tin(IV) complex ofN‐benzoyl‐N‐phenyl‐hydroxamic acid (HX) and chloride ions [SnIVX2Cl2]0is reduced in 2‐propanol solution via two different pathways depending on the scan rate. At scan rates higher than 20 mV/s, the reduction proceeds via [SnIIX2Cl2]2−and [Sn0X(H2O)2]−, and at slower scan rates the reduction proceeds via [SnIIXCl3]2−and [Sn0Cl(H2O)2]−. This is the first time that experiments have indicated the existence of tin0complexes. The studied tinIVcomplex can be used for the determination of tin traces in aqueous solutions. Therefore the tinIVcomplex is preliminarily extracted from aqueous solution and the differential pulse anodic stripping voltammograms are recorded in the organic solution after addition of 2‐propanol. The 3σ limit of detect

ISSN:1040-0397    

DOI:10.1002/elan.1140070306

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractRabbit Cd, Zn‐metallothionein (Cd, ZnMT), synthetically prepared Cd‐metallothionein (CdMT), and apometallothionein (apoMT) have been studied at a mercury electrode and at two types of carbon electrode. At the mercury electrode, different metallothioneins can only be distinguished in cases where their contact with the mercury electrode surface is short. With prolonged time, a mercury compound is formed and its peaks prevail over all the original MT peaks. This conclusion is supported by comparison with apoMT voltammetry at mercury and carbon electrodes. At glassy carbon or carbon composite electrodes, apoMT can be distinguished and determined in the presence of MTs. For both MTs studied, the formation of metal‐free S groups can be observed with prolonged electrolysis at negative potentials; this process is reversible and after several CV cycles, the original structure is reestabl

ISSN:1040-0397    

DOI:10.1002/elan.1140070307

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA carbon paste electrode modified with the ligand propyl gallate is introduced for preconcentration/voltammetric measurements of low levels of uranium. The resulting preconcentrating electrode offers many attractive properties for on‐site sensing of uranium, including high sensitivity and selectivity, self‐cleaning capability, and use of nondeaerated quiescent solutions. The response is characterized with respect to the paste composition, preconcentration period, solution and differential pulse conditions, and other variables. The sensor displays high stability, and can be used repeatedly without regeneration. When coupled to a 100‐ft (30.5‐m) long shielded cable, the electrode offers a remote sensing capability, as illustrated in the determination of uranium in grou

ISSN:1040-0397    

DOI:10.1002/elan.1140070308

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe electrosorption of 2‐propen‐1‐ol, 2‐propin‐1‐ol, 2‐butene‐1, 4‐diol, and 2‐butyne‐l,4‐diol from an aqueous solution of NaClO4at a gold(100) single crystal electrode has been studied by tensammetry. The results are discussed with respect to the surface properties of the single crystal electrode, the different structures of the adsorbed molecules, and possible contributions from the multiple bonds and fu

ISSN:1040-0397    

DOI:10.1002/elan.1140070309

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractMethods for coating cylindrical carbon fiber microelectrodes with Nafion films of different thickness have been developed. It has been shown that it is possible to form thicker Nafion layers on the microelectrodes by adding multiple coats. The charge required to oxidize methylviologen incorporated in Nafion films was used to estimate the average thickness of the Nafion films. The ion‐exchange equilibrium between Nafion film and solution was established more rapidly on the microelectrodes by cylindrical diffusion in the solutions and thicker Nafion films. A procedure for the desorption of viologen and dissolution of Nafion films on microelectrodes has been developed. Their use resulted in regeneration of the microelectrodes before the application of new coatings of Nafio

ISSN:1040-0397    

DOI:10.1002/elan.1140070310

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA novel design for an electrochemical cell for insituatomic force microscopy (AFM) electrochemical measurements with constant volume guard is presented. Decrease in the solution volume during experiments can affect the electrochemical as well as the scanning probe results. The cell is designed for a force microscope with a stationary sample and a scanning probe. Most existing AFM‐electrochemistry cells are limited to small volumes and suffer from high rate of solvent evaporation. The new design enables imaging in small or large volumes under constant volume conditions. Electrochemical measurements using a redox marker in a 0.2 and 2 mL cells, with and without the constant guard, are presente

ISSN:1040-0397    

DOI:10.1002/elan.1140070311

出版商:VCH Verlagsgesellschaft mbH    

年代:1995

数据来源: WILEY