摘要:

AbstractIon‐selective electrodes (ISEs) currently used in clinical analysis are reviewed. The theory of these sensors is outlined. Problems specific for the application of ISEs in clinical analysis are discussed. The prospects for use of new ISEs for clinical purposes are evaluated. More than 50 references are include

ISSN:1040-0397    

DOI:10.1002/elan.1140030802

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractLarge background charges were observed in single potential‐step chronocoulometry obtained with glassy carbon electrodes. Analyses of uncorrected data gave large errors in diffusion coefficients (D) for vitamin B12and ferrocyanide, whose electrode reactions are on opposite sides of 0 V (vs. SCE) where different surface redox processes occur. Subtraction of separately measured average background charge yielded values forDin good agreement with those previously reported. The use of the correct model for the electrode reaction was also necessary for accurate estimation ofD. Even when the final potential was 350 mV positive of the quasireversible ferrocyanide cyclic voltammetric (CV) oxidation peak, the diffusion model gave poor fits to background subtracted chronocoulometric data and errors inD. This is attributed to formation of films on the electrodes at these potentials, especially at pH 12. However, the slow electron transfer model fit these data quite well, provided an accurate value ofD, and also gave rate constants for heterogeneous electron transfe

ISSN:1040-0397    

DOI:10.1002/elan.1140030803

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe electrocatalytic reduction of hydrogen peroxide (H2O2) by horseradish peroxidase (HRP) immobilized on graphite electrodes without the addition of an electron mediator was found to start at + 600 mV vs. Ag/AgCl and the highest current was obtained at about −100 mV. With an applied potential of −50 mV and in the absence of soluble mediator, linear calibration curves for H2O2were obtained between 0.5 μM and 250 μM and for β‐D‐glucose in air‐saturated solution between 2 μM and 0.5 μM (HRP co‐immobilized with glucose oxidase). Cross‐linking the enzymes with glutaraldehyde and bovine serum albumin was found to increase the stability of the sensors without causing mass transfer resistance within the enzyme layer. The response time was 5 seconds both for H2O2and for glucose and the sample through put was 150 samples h−1. The glucose measurements were made in 0.1 M phosphate buffer, pH 6, where no interfering from physiological levels of ascorbic acid, uric acid, or paracetamol (acetaminophe

ISSN:1040-0397    

DOI:10.1002/elan.1140030804

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe response characteristics of a new sensor for determining acetylcholine are reported. The sensor is based on a carbon paste electrode containing the enzymes acetylcholinesterase and choline oxidase and the electron transfer mediator tetrathiafulvalene (TTF). TTF is shown to efficiently reoxidize the reduced flavin adenine dinucleotide centers of choline oxidase. Acetylcholine calibration graphs are obtained in the range 10−6to 10−3M in pH 7.0 phosphate buffer, and the sensors are shown to operate efficiently at low applied potentials, where electrochemical interference due to oxidation of ascorbic acid is minimi

ISSN:1040-0397    

DOI:10.1002/elan.1140030805

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe electrochemical oxidation of Langmuir–Blodgett films ofn‐doxyl‐stearates (n= 5, 7, 12, 16; present as their cadmium salts) on indium tin oxide electrodes has been studied. Then= 12 species gives cyclic voltammograms (CVs) that reveal split peaks consistent with the formation of an ordered partially oxidized layer with a structure controlled by interactions of longer range than nearest nei

ISSN:1040-0397    

DOI:10.1002/elan.1140030806

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractMicrodisk and microhole array electrodes were used to construct amperometric glucose biosensors based on the detection of hydrogen peroxide. All‐chemical methods such as platinization, glucose oxidase immobilization, and electropolymerization permit electrodes of any size, shape, or surface complexity to be used for biosensors. This also gives the biosensor surface a multifunctional character, where the platinization decreases the operating potential, the immobilized enzyme provides the specificity, and the electropolymerized film prevents interferences and fouling. All of these functions are accomplished in a layer that is about 10 nm thick. The microdisk and microhole biosensors were linear to about 3 mM and 4 mM glucose, respectively, and were accurate, as checked by standard reference seru

ISSN:1040-0397    

DOI:10.1002/elan.1140030807

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractNovel potentiometric membrane electrodes with high selectivity to urea over the 1.3 × 10−4− 1.1 × 10−2M and 4.0 × 10−4− 1.0 × 10−2M concentration range were constructed by immobilized soybean meal at a NH3or CO2gas‐sensing electrode. The sensor does not require fresh bean tissue so it is not limited by the season of the year. The influence of some experimental parameters, including buffer composition, pH, and immobilization techniques are discussed. The resulting electrode is found to be a viable alternative to the enzym

ISSN:1040-0397    

DOI:10.1002/elan.1140030808

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe use of the rotating disk electrode (RDE) for batch injection analysis (BIA) is illustrated. The technique involves injections of microliter samples into a large‐volume blank solution, at a fixed location below the disk center. Transient response peaks—similar to those of flow injection analysis—are observed, reflecting the transport of the sample plug toward and away from the RDE. The effects of various experimental variables on the BIA/RDE operation are described. Injection rates of several thousand samples per hour can be achieved, with relative standard deviations of 1–3%, and detection limits at the micromolar (ng

ISSN:1040-0397    

DOI:10.1002/elan.1140030809

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe on‐line high‐performance liquid chromatography‐electrochemistry‐thermospray mass spectrometry (LCEC‐LC/MS) for separation and identification of the phenolic isoflavones genistein, formononetin, and Biochanin A is described. The isoflavones are separated on a C‐18 reversed phase column with methanol: 0.1 M ammonium acetate pH (70:30 v/v) as eluent, which is compatible for both LCEC and LC/MS detection. Low ng detection is achieved with a conventional glassy carbon thin‐layer electrochemical cell at 1.3 V vs. Ag/AgCl. Selected ion monitoring (SIM) mode LCMS results in detection levels at the 20–50 ng range, and the compounds are positively identified. In the on‐line detection, the electrochemical cell is connected to the thermospray and the column effluent flows from the working electrode into the heated thermospray capillary tube. The results show that on‐line coupling between a thin‐layer LCEC and a thermospray‐LC/MS can be used to characte

ISSN:1040-0397    

DOI:10.1002/elan.1140030810

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractTransport of permitted and Donnas‐forbidden ions as well as neutral solutes through ion exchange membranes have been investigated in continuous flow‐through configurations in the presence and absence of an alternating electrical field (0.05–100 kHz, 0–40 V p‐p). There is no discernible effect on the transport rate of forbidden ions and neutral solutes but very significant increases in steady state transmembrane transport occur for permitted ions. At least for cation exchangers, an increase in effective ion exchange capacity also appears to occur in the presence of the field. These effects are ascribed to the greater kinetic energy of the ions exposed to the alternating field and thus to the higher effective thermodynamic temperature the ions e

ISSN:1040-0397    

DOI:10.1002/elan.1140030811

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY