摘要:

AbstractThe use of chemically modified electrodes (CMEs) for liquid chromatography and flow‐injection analysis is reviewed. Electrochemical detection with CMEs based on electrocatalsis, permselectivity, ion flow in redox films, and ion transfer across the water–solidified nitrobenzene interface is discussed in terms of improving the stability, selectivity, and scope of electrochemical detectors and the detection of electroinactive substances. More than 90 references are inclu

ISSN:1040-0397    

DOI:10.1002/elan.1140030102

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractCarbon composite electrodes modified with silica gel exhibit properties analogous to those of an ultramicroelectrode array in voltammetric measurements. The limiting current in linear scan voltammetry is independent of the potential scan rate in certain scan rate regions. The possibility of using high potential scan rates is advantageous analytically, both in direct voltammetric determinations and in analyses involving accumulation of the analyte on the surface of the working electrode.

ISSN:1040-0397    

DOI:10.1002/elan.1140030103

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe behavior of oxyethylated oxoalcohols (e.g., Oxetals D104, T105, and C114, and oxyethylatedn‐dodecanol BRIJ‐35) was investigated. The dependence of peak height on concentration of surfactant, preconcentration time, and preconcentration potential was examined. To improve the analytical signal of Oxetals C114 and T105, the influence of methanol on their tensammetric curves was investigated. Roughly, all the surfactants exhibit two peaks: a wide one, corresponding the monomer form, which shifts toward the negative direction with an increase in concentration, and a narrow one, corresponding to the associate form, whose position is stable. Oxetals C114 and T105 exhibit additional peaks, which complicate the determination. The addition of 20% of methanol removes such difficulties and only one peak rema

ISSN:1040-0397    

DOI:10.1002/elan.1140030104

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA new methodology for the study of luminescence from photoexcited electrogenerated species is presented. A suitable optically transparent thin‐layer electrode compatible with fluorescence spectrometer was developed, and this was used to study luminescence from the radical cation of tris(4‐methylphenyl)amine and the radical anion of 9,10‐anthracenedione electrogenerated in

ISSN:1040-0397    

DOI:10.1002/elan.1140030105

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA platinum electrode coated with polyaniline (PA) was examined as a Potentiometric or an optical sensor for dissolved oxygen, and the results are reported. While the polymer‐modified electrode behaved satisfactorily as a potentiometric sensor, its optical response (i.e., absorbance) gave a narrow linear region for varied oxygen concentrations. This conducting polymer‐coated electrode was characterized to give approximately 97 mV/decade of the oxygen concentration and a voltage signal range of about 400 mV, representing at least three orders of magnitudes of dynamic linearity over the dissolved oxygen concentration. The potentiometric sensing electrode showed reasonably short response times, excellent reproducibility, and good stability. A detection limit of about 5 × 10−7mol/L of dissolved oxygen was estimated from the potentiometric response of PA‐coated el

ISSN:1040-0397    

DOI:10.1002/elan.1140030106

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractRuthenium dioxide‐(RuO2)‐containing carbon paste electrodes exhibiting electrocatalytic responses toward alcohols are described. The electrocatalytic behavior is exploited for developing a highly stable and sensitive flow‐detection scheme for simple alcohols with a constant‐potential operation (+0.4 V vs. Ag/AgCl). The optimization of the system with respect to variables such as pH, flow rate, operating potential, and RuO2–surface “loading” is reported. The electrode response as stable over 2 weeks with a signal loss of 6%. Repeated injections (60) of methanol over a 120 minute period yielded a relative standard deviation of 3.4%. Detection limits for the various alcohols are dependent on the number and position of the hydroxyl groups, with limits ranging from 30 ng for glycerol to 3 μg for ethanol. Use of these electrodes in liquid chromatography with electrochemical detectio

ISSN:1040-0397    

DOI:10.1002/elan.1140030107

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe adsorptive voltammetric behavior of the binding proteins avidin and streptavidin was investigated at a stationary mercury drop electrode. It is demonstrated that, although streptavidin contains no disulfide linkages or sulfur‐containing amino acids, it gives rise to voltammetric behavior similar to avidin, which is a glycoprotein containing two cysteine residues per subunit and one interchain disulfide linkage. The adsorptive accumulation of both proteins was investigated both at open circuit and under electrolytic conditions. It is shown that avidin shows preferential adsorption characteristics under open circuit conditions, and under electrolytic conditions when the potential of the electrode was held at positive potentials. Streptavidin, on the other hand, shows preferential adsorption characteristics when accumulation is carried out at open circuit. This behavior is explained by considering the charged nature of the proteins under the experimental conditions used in this study. It would appear, therefore, that the voltammetric peaks obtained for globular and other proteins not containing prosthetic groups are due in part to processes other than the simple reduction of the disulfide linkag

ISSN:1040-0397    

DOI:10.1002/elan.1140030108

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA new method of flow‐through coulometry is presented. The fundamental principle is different from that in the conventional method. Two working electrodes are involved in the coulometric cell. An electrolysis efficiency of only 20 to 30% is required for the measurement. From the response coulombs (Q1andQ2) of the two working electrodes, the charge (Qc) calculated by using Equation 4 correspond to an electrolysis efficiency of 100% and is independent of the temperature and flow rat

ISSN:1040-0397    

DOI:10.1002/elan.1140030109

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have developed a disposable bacterial CO2sensor employing a miniature Clark‐type oxygen electrode and autotrophic bacteria. To make the sensitive area less vulnerable to stress, to facilitate CO2diffusion through the sensitive area, and to make the application to biosensors easier, the sensor structure was simplified by immobilizing the bacteria in an oxygen electrode cell along with a 0.1 M KCl electrolyte solution. We developed a novel process that allows immobilization of bacteria in a small sensitive area, thereby improving the response time. The response time of this CO2sensor ranged from 1 to 3 minutes. A linear relationship was obtained for NaHCO3concentrations between 0.5 and 3.5 mM (at 32°C and pH 5.5). The CO2sensor can be used up to 10 times before dispos

ISSN:1040-0397    

DOI:10.1002/elan.1140030110

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY

摘要:

AbstractFree and total cholesterols in human serum have been determined by controlled‐potential coulometry with porous carbon felt electrodes. In such a coulometric cell, a small amount of sample solution was dropped on the carbon felt dipped into electrolyte containing enzymes and a mediator. Hydrogen peroxide is produced by the enzymatic reaction of cholesterol catalyzed by cholesterol oxidase, and the complete electroreduction of hexacyanoferrate(III) ions [produced by the reaction of hexacynoferrate(II) ions and hydrogen peroxide catalyzed by peroxidase] was carried out under controlled‐potential conditions. In the case of determining total cholesterol in human serum, cholesterol esters were converted to free cholesterol by cholesterol esterase reaction prior to the addition of the sample solution into electrolyte. The conversion ratios of free cholesterol to hydrogen peroxide were found to be 85–89% (RSD<6%). The electrolysis time of one sample was less than 5 minutes. Immobilization of cholesterol oxidase to the carbon felt surface was attempted; the activity of cholesterol oxidase, Immobilized by the diazo‐coupling method began to decrease 3 days after the immobil

ISSN:1040-0397    

DOI:10.1002/elan.1140030111

出版商:VCH Verlagsgesellschaft mbH    

年代:1991

数据来源: WILEY