Determination of sulfadiazine and sulfamethoxazole by capillary electrophoresis with end-column electrochemical detection

Capillary electrophoresis (CE) with end-column electrochemical detection (EC) of sulfadiazine (SDZ) and sulfamethoxazole (SMZ) is described. Under the optimum conditions, SDZ and SMZ were separated satisfactorily, and a highly sensitive and stable response was obtained at a potential of 1.1 V versus Ag/AgCl. Optimized end-column detection provides detection limits as low as 0.1 mu M for both compounds, which corresponds to 0.024 and 0.021 fmol with peak efficiencies of 394000 and 335000 theoretical plates for SDZ arid SMZ, respectively. The calibration graph was linear over three orders of magnitude. The relative standard deviations (n = 12) of peak currents and migration times were 2.3 and 2.7%, and 0.8 and 1.3%, respectively, for the two compounds. The proposed method was applied to the analysis of tablets and human urine samples with satisfactory results.

Investigation of oxygen- and hydrogen peroxide-reduction on platinum particles dispersed on poly(o-phenylenediamine) film modified glassy carbon electrodes

Composite membrane modified electrodes were prepared by electrochemical deposition of platinum particles in a poly(o-phenylenediamine) (PPD) him coated on glassy carbon (GC) electrodes. The modified electrodes showed high catalytic activity towards the reduction of oxygen and hydrogen peroxide. A four-electron transfer process predominated the reduction process. The pH dependence and the stability of the electrodes were also studied.

The electrochemical study of oxidation-reduction properties of horseradish peroxidase

Oxidation-reduction properties of horseradish peroxidase (HRP) have been investigated by using direct electrochemical methods. Two successive separated distinct one-electron processes of HRP were obtained and the related physiological processes were described. The monolayer coverage of HRP at the electrode surface is about 50 pmol/cm(2). UV-Vis spectrophotometry and stable amperometry prove that the enzyme electrode possesses catalytic activity for H2O2 in the absence of a mediator and it might offer an opportunity to build the third generation of biosensors for analytes, such as H2O2, glucose and cholesterol etc. (C) 1997 Elsevier Science S.A.

Cyclic voltammetry of dye-modified supported bilayer lipid membranes (s-BLMs)

The voltammetric behaviour of dye-modified supported bilayer lipid membranes is investigated. (C) 1997 Elsevier Science S.A.

Organic phase enzyme electrodes based on organohydrogel

A dimethylformamide-polyhydroxyl cellulose organo-hydrogel has been prepared, and its applications for enzyme immobilization in construction of organic phase biosensors have been exploited. With horseradish peroxidase, tyrosinase, and bilirubin oxidase immobilized in the organohydrogel, enzyme electrodes can be operated in various situations, including aqueous buffer, oil/water mixtures, and anhydrous organic solvents, and even in dimethylformamide, to determine analytes of different solubilities, e.g., organic peroxides, phenolic compounds and bilirubin. Biosensing has no restrictions in terms of measuring media and solubilities of analytes.

Determination of hydroxylamine by capillary electrophoresis electrochemical detection with a palladium-particle modified carbon fiber microdisk array electrode

A highly dispersed ultramicro palladium-particle modified carbon fiber microdisk array electrode (Pd-CFE) was employed for capillary electrophoresis-electrochemical (CEEC) detection of hydroxylamine (HA). The Pd particles obtained were in the nanometer scale, had a high electrocatalytic activity towards HA and exhibited good reproducibility and stability. A linear relationship between the current and the analyte concentration was found between 5 x 10(-6) and 1 x 10(-3) mol/l of HA with a correlation coefficient of 0.9992. The detection limit was 5 x 10(-8) mol/l. The applicability of the method for the determination of HA in river water and waste water was investigated.

Viologen-thiol self-assembled monolayers for immobilized horseradish peroxidase at gold electrode surface

A stable, well-behaved self-assembled monolayer (SAM) of viologen-functionalized thiol was used to immobilize and electrically connect horseradish peroxidase (HRP) at gold electrode. Viologen groups in SAMs facilitated the electron transfer from the electrode to the protein active site so that HRP exhibited a quasi-reversible redox behavior. HRP adsorbed in the SAMs is very stable, and close to a monolayer with the surface coverage of 6.5 x 10(-11) mol/cm(2). The normal potential of HRP is -580 mV vs Ag/AgCl corresponding to ferri/ferro active center and the standard electron transfer rate constant is 3.41 s(-1) in 0.1 M phosphate buffer solution (pH 7.1). This approach shows a great promise for designing enzyme electrodes with other redox proteins and practical use in tailoring a variety of amperometric biosensor devices. Copyright (C) 1997 Elsevier Science Ltd.

Permselectivity of 4-aminophenol, paracetanol and phenacetin on the self-assembled n-alkanethiol monolayer modified gold electrode

The gold electrodes coated by n-alkanethiol with various chain lengths were used to study the permeability of uric acid, ascorbic acid, 4-aminophenol, paracetanol and phenacetin by means of linear sweep voltammetry. The results show that the optimum chain length is n=10. The improvements in the selectivity and the stability of the amperometric detection of these compounds in a flow stream were obtained by n-alkanethiol self assembled monolayers modified electrodes based on their differences in the hydrophobicity and the permeability.

Electrochemical behaviour of TCNQ on platinum supported BLMs

The electrochemical behaviour of TCNQ modified S-BLM has been investigated through capacitor measurement and cyclic voltammetry (CV) which shows the surface wave behaviour of the TCNQ redox form. The voltammetry CV has shown different pairs peak at different scan rates and a possible explanation is provided.

Detection of hydrazine, methylhydrazine, and isoniazid by capillary electrophoresis with a palladium modified microdisk array electrode

A palladium particle-modified carbon fiber microdisk array electrode was designed and employed in capillary electrophoresis for the simultaneous detection of hydrazine, methylhydrazine, and isoniazid. The Pd-modified microdisk electrode had high catalytic ability for hydrazines and exhibited good reproducibility and stability. The response for hydrazine was linear over 3 orders of magnitude with a correlation coefficient of 0.993. The detection limits far hydrazine, methylhydrazine, and isoniazid were 1.2, 2.1, and 6.2 pg, respectively.

The fabrication and performance of an Ag/AgCl reference electrode in human serum

A simple set of electric circuits was used to assemble a pulse generator. With pulse potentials and under galvanostatical control, a clean silver wire was anodized electrochemically for 0.2-0.5 min in 1.0 moll(-1) HCl with a pulse current density of 20 mA cm(-2), and the pulse wave parameters of t(a)/t(c) = 1 and a cycle of 4 s forming an Ag/AgCl reference electrode. Even though the AgCl layer was consumed during the working period when the Ag/AgCl electrode was used as a cathode, the AgCl layer could be in situ recovered electrochemically in serum used when a reversed potential was applied to the electrode system immediately after the measuring program was finished. The current response curve of the anode indicated that an AgCl layer in high density was basically accomplished during the first 6 pulse cycles in human serum. In order to keep a stable and uniform AgCl layer on the reference electrode after each measuring cycle, the ratio of the recovery time (t(r)) to the working time (t(w)) was measured and the smallest value was obtained at 0.03. The open-circuit potential of the Ag/AgCl electrode with respect to a SCE in 0.1 moll(-1) KCl was monitored over a period of 14 days and the mean value was 40.09 mV vs SCE with a standard deviation of 2.55 mV. The potential of the Ag/AgCl reference electrode did remain constant when the measurements were repeated more than 600 times in undiluted human serum with a standard deviation of 1.89 mV. This study indicated that the Ag/AgCl reference electrode could been rapidly fabricated with a pulse potential and could be used as a reference electrode with long-term stable properties in human serum samples.

ELECTROCATALYTIC OXIDATION AND FLOW DETECTION OF CYSTEINE AT AN AQUOCOBALAMIN ADSORBED GLASSY-CARBON ELECTRODE

A chemically modified electrode (CME) constructed by adsorption of aquocobalamin (VB12a) onto a glassy carbon electrode surface was demonstrated to catalyze the electro-oxidation of cysteine, a sulfhydryl-containing compound. The sulfhydryl oxidation occured at 0.54-0.88 V vs. Ag/AgCl depending on pH value (3.0-10.0). The electrocatalytic behavior of cysteine is elucidated with respect to solution pH, operating potential and other variables as well as the CME preparation conditions. When used as the sensing electrode in flow injection amperometric detection, the CME permitted detection of the compound at 0.8 V. The detection limit was 1.7 pmol. The linear response range went up to 1.16 nmol. The stability of the CME was shown by RSD (4.2%) over 10 repeated injections.

DETERMINATION OF AMINOPYRINE AND ITS METABOLITE IN BIOLOGICAL FLUID BY LIQUID-CHROMATOGRAPHY ELECTROCHEMISTRY WITH A GLASSY-CARBON ELECTRODE DISPERSED WITH ALPHA-ALUMINA PARTICLES

A sensitive high-performance liquid chromatographic method has been developed for the quantitative determination of aminopyrine (AM) and its metabolite 4-aminoantipyrine (AAN). The method utilizes reverse-phase chromatography/amperometric detection with a glassy carbon electrode dispersed with alpha-arumina particles as the working electrode, on which the oxidation of AM and AAN was greatly improved compared with that on a bare glassy carbon electrode. As a result, the detection limit was as low as 1.4 ng for AM and 0.8 ng for AAN, and the calibration plots for the above compounds have wide linear ranges from 100 ng/mL to 100 mu g/mL and 60 ng/mL to 80 mu g/mL (for AM and AAN, respectively). The above method was applied for the detection of these materials in human urine with satisfactory results.

Electrocatalytic Oxidation of Dihydric Phenol on Polypyrrole Film Modified Electrodes

The electrochemical behavior of catechol, hydroquinone and resorcinol on GC and PPy/GC electrode surface were studied by CV and RDE method. The results indicated that these three substance could be oxidized electrocatalytically on PPy film electrode. The possibility of fabrication of amperometric electrochemical sensor for catechol was also studied.

DIRECT-INJECTION OF URINE AND DETERMINATION OF ACETAMINOPHEN BY MICELLAR LIQUID-CHROMATOGRAPHY WITH A WALL-JET CELL CARBON-FIBER MICROELECTRODE

A wall-jet cell/carbon fibre microelectrode detector was designed and used for the micellar liquid chromatographic assay of acetaminophen. The separations were carried out in an analytical column packed with C-18 stationary phase and the mobile phase was