Chemically Modified Electrode Research Articles

In Vivo Determination of Tetrahydrobiop- terin and Monoamine Neurotransmitters in Rat Brain by Liquid Chromatography with a Nano Crystalline Mn-Doped Lead Dioxide Film Modified Electrode

The fabrication and application of a novel electrochemical detector (ED) with nano crystalline Mn-doped lead dioxide film chemically modified electrode (CME) for liquid chromatography (LC) were described. The Mn-doped PbO2 film was characterized by scanning tunnel microscope. The electrochemical behaviors of tetrahydrobiopterin, monoamine neurotransmitters and their metabolites at the CME were investigated by cyclic voltammetry and differential pulse voltammetry. It was found that the CME exhibited efficiently electrocatalytic effect on the current response of the seven analytes and the linear ranges of them were over three orders of magnitude with the detection limits being 5.0 × 10−10 mol L−1 for tetrahydrobiopterin, 2.5 × 10−10 mol L−1 for dopamine, 2.0 × 10−10 mol L−1 for norepinephrine, 5.0 × 10−10 mol L−1 for serotonin, 4.0 × 10−10 mol L−1 for 3,4-dihydroxyphenylacetic acid, 2.0 × 10−9 mol L−1 for homovanillic acid, 1.0 × 10−9 mol L−1 for 5-hydroxyindoleacetic acid. For its stability, sensitivity, convenience in preparing and long-life of activity, the Mn-doped PbO2 electrode is therefore suitable for determination of real samples. Coupled with microdialysis sampling, the application of this method for the analysis of tetrahydrobiopterin, monoamine neurotransmitters and their metablites in rat brain was satisfactory.

Amperometric determination of ( R)-salsolinol, ( R)- N-methylsalsolinol and monoamine neurotransmitters with liquid chromatography using functionalized multi-wall carbon nanotube modified electrode in Parkinson’s patients’ cerebrospinal fluid

The fabrication and application of a novel electrochemical detection (ED) system with the functionalized multi-wall carbon nanotubes (MWNTs) chemically modified electrode (CME) for liquid chromatography (LC) were described. The electrochemical behaviors of dopamine (DA) at the CME were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the CME exhibited efficiently electrocatalytic effect on the current responses of ( R)-salsolinol ((R)-Sal), ( R)- N-methylsalsolinol ((R)-NMSal), and monoamine neurotransmitters with high sensitivity, stability, and long-life of activity. In LC–ED, all (R)-Sal, (R)-NMSal, DA, norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA) had good and stable current responses at the CME. The linear ranges of the nine analytes were over three orders of magnitude ( R 2>0.995). The application of this method coupled with microdialysis sampling for the determination of (R)-Sal, (R)-NMSal, and monoamine neurotransmitters in Parkinson’s patients’ cerebrospinal fluid was satisfactory.

Simultaneous Determination of Aromatic Amines by Liquid Chromatography Coupled with Carbon Nanotubes/Poly (3-methylthiophene) Modified Dual-Electrode

Liquid chromatography with amperometric detection (LC-AD) is developed and applied to simultaneously determine five aromatic amines. In the LC-AD, a new carbon nanotubes/poly(3-methylthiophene) modified dual-electrode is fabricated and then used as the working electrode. It is found that this chemically modified electrode (CME) exhibits efficiently electrocatalytic oxidation for aromatic amines with relatively high sensitivity, stability and long-life. Thus, lower detection in LC-AD can be achieved, which are 4.0 × 10−8 mol L−1 for aniline, 1.6 ×10−7 mol L−1 for 4-nitroaniline, 1.0 × 10−7 mol L−1 for 4-chloroaniline, 1.5 × 10−7 mol L−1 for 1-naphthylamine, 1.7 × 10−7 mol L−1 for 2-bromoaniline. The recoveries of the five analytes are also determined, which range between 0.95 and 1.05 for drinking water, 0.86 and 1.10 for the LiWa River water.

Liquid chromatography with amperometric detection at a nano crystalline Ce-doped lead dioxide film modified electrode for determination of (R)-Salsolinol, (R)-N-methylsalsolinol and monoamine neurotransmitters in Parkinsonian patients' cerebrospinal fluid

The fabrication and application of a novel electrochemical detector (ED) with nano crystalline Ce-doped lead dioxide film chemically modified electrode (CME) for liquid chromatography (LC) were described. The Ce-doped PbO(2) film was characterized by X-ray diffractometer (XRD) and scanning tunnel microscope (STM). The electrochemical behaviors of (R)-Salsolinol ((R)-Sal) at the CME were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that the CME exhibited an efficiently electrocatalytic effect on the current responses of (R)-Sal, (R)-N-methylsalsolinol ((R)-NMSal) and monoamine neurotransmitters. In LC-ED, all (R)-Sal, (R)-NMSal, dopamine (DA), norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) had good and stable current responses at the CME. The linear ranges of the nine analytes were over three orders of magnitude (R(2) > 0.995). The application of this method coupled with microdialysis sampling for the determination of (R)-Sal, (R)-NMSal and monoamine neurotransmitters in Parkinsonian patients' cerebrospinal fluid (CSF) was satisfactory.

Flow-injection analysis and voltammetric detection of NADH with a poly-Toluidine Blue modified electrode.

Poly-Toluidine Blue film was prepared by electrooxidative polymerization at a glassy carbon electrode in a phosphate buffer solution. The resulting chemically modified electrode (CME) exhibited excellent electrocatalysis toward the oxidation of reduced nicotinamide coenzyme (NADH) with over a 450 mV decrease of the overpotential compared with that at a bare glassy carbon electrode. Two electrochemical determinations of NADH, cyclic voltammetry and flow injection analysis, were established based on the electrocatalytical performance of the resulting modified electrode. Under an identical determinate condition, the voltammetric detection for NADH gave a detection limit of 3.3 micromol L(-1) with a linear concentration range of 9.1 micromol L(-1) to 1.8 mmol L(-1). As a detector in a flow-injection system, the CME gave a detection limit of 0.1 micromol L(-1) for NADH with a linear concentration range of 1.0 micromol L(-1) to 3.2 mmol L(-1). Obviously, flow-injection analysis is superior to voltammetric detection in NADH determination for its lower detection limit and wider detectable linear range.

Recent Updates of Chemically Modified Electrodes in Analytical Chemistry

AbstractThis review article updates recent developments in chemically modified electrodes (CMEs) towards analytical applications for the year of 2000–2002 with 179 references. The broad topics are subdivided into four main categories: i) physisorption/chemisorption, ii) covalently linked, iii) homogenous (uniform) multilayer and iv) heterogeneous (non‐uniform) multilayer CMEs. The criteria for the preparation of CMEs in elecrocatalytic systems are clearly described in Section 1. Some of the encouraging results related to Au‐nanoparticles for DNA detection and new ceramic carbon, carbon nanotubes, copper‐plated screen‐printed and Nafion/lead ruthenate pyrochlore CMEs for catalytic application were especially discussed in this review.

In Vivo Monitoring of the Thiols in Rat Striatum by Liquid Chromatography with Amperometric Detection at a Functionalized Multi‐Wall Carbon Nanotubes Modified Electrode

AbstractA new chemically modified electrode (CME) was fabricated, which was based on the immobilization of multi‐wall carbon nanotubes fuctionalized with carboxylic group (MWNT‐COOH). The results indicated that the CME exhibited efficiently electrocatalytic oxidation for L‐cysteine and glutathione with relatively high sensitivity, stability and long‐life. Coupled with HPLC, the MWNT‐COOH CME was utilized for amperometric detection of the thiols. The peak currents of L‐cysteine and glutathione were linear to their concentrations ranging from 3.0×10−7 to 1.0×10−3 mol/L with the calculated detection limit (S/N=3) of 1.2×10−7, 2.2×10−7 mol/L, respectively. The method had been successfully applied to assess the contents of L‐cysteine and glutathione in rat striatal microdialysates.

Determination of electroinactive organic acids in red wine by ion-exclusion chromatography using a poly-o-phenylenediamine film modified electrode

In this article, an ion-exclusion chromatography method combined with amperometric detection at a poly-o-phenylenediamine (POPD) film modified gold electrode provided a convenient analytical method for the determination of some electroinactive organic acids. The electrochemical behaviors of some aliphatic acids at POPD chemically modified electrode (CME) have been investigated by Differential Pulse Voltammetry (DPV). Under the optimum ion chromatographic conditions tartaric acid, citric acid, malic acid, formic acid, acetic acid and succinic acid could be separated in 15 min. The detection limits of these organic acids were 3.28×106 mol L−1 for tatartic acid, 3.62×106 mol L−1 forcitric acid, 3.84×106 mol L−1 for malic acid, 3.26×106 mol L1 for formic acid, 4.42×106 mol L1 for acetic acid and 3.66×106 mol L1 for succinic acid (S/N=3), respectively. The proposed method had been applied to the measurement the organic acids in red wine with satisfactory results. The electrode was very stable and there was no evidence of chemical and mechanical deterioration about 10 days.

Electrochemical activation of electrodes for amperometric detection of nitric oxide

An open question in the literature of nitric oxide detection was investigated: does electrochemical activation account for the enhanced properties of certain presumed chemically-modified electrodes? Uniform electrodes of graphite, iridium, palladium, platinum, and ruthenium were exposed to potential cycling and then tested for amperometric response to nitric oxide to identify principles that govern electrochemical activation of nitric oxide electrodes. These electrodes were compared to similar electrodes that were not cycled. Only cycled graphite and ruthenium showed significantly increased responses. Graphite demonstrated enhanced performance after exposure to cycling potentials at which oxygen, CO 2, and soluble carbonates form, suggesting that erosion of the electrode enhanced its response by increasing the surface area accessible to nitric oxide. This may explain the performance of carbon fibers cycled to the same potentials in solutions containing metalloporphyrins. The response of ruthenium was enhanced after cycling to less extreme potentials at which soluble species do not form and at which a metallic conductive oxide, RuO 2, could lay down a stable, adherent layer on the electrode surface. Cycled ruthenium also exhibited a much greater increase in capacitance after cycling, consistent with the formation of a conductive surface layer.

Study of the interaction of 6-mercaptopurine with protein by microdialysis coupled with LC and electrochemical detection based on functionalized multi-wall carbon nanotubes modified electrode

Microdialysis sampling coupled with liquid chromatography and electrochemical detection (LC–ECD) was developed and applied to study the interaction of 6-Mercaptopurine (6-MP) with bovine serum albumin (BSA). In the LC–ECD, the multi-wall carbon nanotubes fuctionalized with carboxylic groups modified electrode (MWNT-COOH CME) was used as the working electrode for the determination of 6-MP. The results indicated that this chemically modified electrode (CME) exhibited efficiently electrocatalytic oxidation for 6-MP with relatively high sensitivity, stability and long-life. The peak currents of 6-MP were linear to its concentrations ranging from 4.0×10 −7 to 1.0×10 −4 mol l −1 with the calculated detection limit (S/N=3) of 2.0×10 −7 mol l −1. The method had been successfully applied to assess the association constant (K) and the number of the binding sites (n) on a BSA molecular, which calculated by Scatchard equation, were 3.97×10 3 mol −1 l and 1.51, respectively. This method provided a fast, sensible and simple technique for the study of drug–protein interactions.

Amperometric determination of 6-mercaptopurine on functionalized multi-wall carbon nanotubes modified electrode by liquid chromatography coupled with microdialysis and its application to pharmacokinetics in rabbit

In this paper, multi-wall carbon nanotubes fuctionalized with carboxylic groups modified electrode (MWNT-COOH CME) was fabricated. This chemically modified electrode (CME) can be used as the working electrode in the liquid chromatography for the determination of 6-mercaptopurine (6-MP). The results indicate that the CME exhibits efficiently electrocatalytic oxidation for 6-MP with relatively high sensitivity, stability and long-life. The peak currents of 6-MP are linear to its concentrations ranging from 4.0×10 −7 to 1.0×10 −4 mol l −1 with the calculated detection limit ( S/ N=3) of 2.0×10 −7 mol l −1. Coupled with microdialysis, the method has been successfully applied to the pharmacokinetic study of 6-MP in rabbit blood. This method provides a fast, sensible and simple technique for the pharmacokinetic study of 6-MP in vivo.

Preparation of multiwall carbon nanotubes film modified electrode and its application to simultaneous determination of oxidizable amino acids in ion chromatography

A multiwall carbon nanotubes (MWNTs) film modified electrode was prepared and used as an amperometric sensor for the simultaneous determination of oxidizable amino acids including cysteine, tryptophane and tyrosine. The electrochemical behaviors of these amino acids at this modified electrode were studied by cyclic voltammetry (CV). The results indicated that the MWNTs chemically modified electrode (CME) exhibited efficient electrocatalytic activity towards the oxidation of these amino acids with relatively high sensitivity, stability and long-life. Following separation by ion chromatography (IC) with 2.0×10 −3 mol l −1 citric acid buffer solution (pH 6.5) as eluent, cysteine, tryptophane and tyrosine could be determined by the MWNTs CME successfully. Under the optimal conditions, the detection limits were 7.0×10 −7 mol l −1 for cysteine, 2.0×10 −7 mol l −1 for tryptophane and 3.5×10 −7 mol l −1 for tyrosine at the signal-to-noise of 3, respectively. The method was applied successfully to the determination of these substances in plasma.

Liquid chromatography with amperometric detection using functionalized multi-wall carbon nanotube modified electrode for the determination of monoamine neurotransmitters and their metabolites

The fabrication and application of a novel electrochemical detection (ED) method with the functionalized multi-wall carbon nanotubes (MWNTs) chemically modified electrode (CME) for liquid chromatography (LC) were described. The electrochemical behaviors of dopamine (DA) and other monoamine neurotransmitters at the CME were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results indicated that the CME exhibited efficient electrocatalytic effects on the current responses of monoamine neurotransmitters and their metabolites with high sensitivity, high stability and long-life activity. In LC–ED, DA, norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) had good and stable current responses at the CME. The linear ranges of seven analytes were over four orders of magnitude and the detection limits were 2.5·10 −10 mol/l for DA, 2.5×10 −10 mol/l for NE, 5.0·10 −10 mol/l for MHPG, 3.0·10 −10 mol/l for DOPAC, 3.5·10 −10 mol/l for 5-HT, 6.0·10 −10 mol/l for 5-HIAA, 1.25·10 −9 mol/l for HVA. The application of this method coupled with microdialysis sampling for the determination of monoamine neurotransmitters and their metabolites in Parkinsonian patients’ cerebrospinal fluid was satisfactory.

Silver Hexacyanoferrate Film Directly Modified Electrode as a Potentiometric Sensor for Potassium Ion

A chemically modified electrode (CME) was fabricated by direct modification of a silver electrode with a thin film of silver hexacyanoferrate. The modified electrode was used as a potentiometric sensor for the determination of potassium ion. The sensor exhibits a response to potassium ion in a wide concentration range from 8.0 × 10−5 to 1.0 M with a low detection limit of 4.0 × 10−5 M. The potassium-selective electrode has a relatively short response time. It has a good sensitivity with a near-Nernstian slope of 53–57 mV/decade and good selectivity in the presence of possible interferences. The electrode response is highly sensitive to some controllable parameters mainly the thickness of electroactive film which is controlled by the charge passed in the cell during the deposition of the film. Stability of the directly modified electrode and its potentiometric response were also investigated during long-term usage, which were indicative of the possibility of the potassium-selective electrode for using in a long period.

Simultaneous determination of the monoamine neurotransmitters and glucose in rat brain by microdialysis sampling coupled with liquid chromatography-dual electrochemical detector

A new type of chemically modified electrode based ring–disk electrode as the dual electrochemical detector (DECD) for high-performance liquid chromatography (HPLC) to simultaneously determine the monoamine neurotransmitters and glucose is described. The ring electrode was modified with an ion-exchange polymer-overoxidized polypyrrole (OPPy) and the disk electrode was modified with nano Au colloid and glucose oxidase (GOD). The electrochemical behaviors of dopamine (DA) and ascorbic acid (AA) at the OPPy chemically modified electrode (CME) were investigated by differential pulse voltammetry (DPV). It was found that the CME could permeate dopamine cations and repelled the ascorbate anions, which could be used to determine the monoamine neurotransmitters and avoid the interference of AA. The electrochemical behavior of glucose at the Nafion/GOD–Au colloid/GC CME was investigated by amperometry and flow injection analysis (FIA). It was found that the sensitivity of the CME increased apparently in determination of glucose. In order to obtain better separation and current responses of the analytes in HPLC-DECD, several operational parameters have been investigated. Under the optimum conditions, the method showed good stability and reproducibility. The application of this method coupled with microdialysis sampling for in vivo simultaneous determination of monoamine neurotransmitters and glucose in rat brain was satisfactory.

Tendências em modificação de eletrodos amperométricos para aplicações eletroanalíticas

The most relevant advances on the analytical applications of chemically modified electrodes (CME) are presented. CME have received great attention due to the possibility of electrode surface modification including chemisorption, composite generation and polymer coating. In recent years, the interest in CME has increased overall to improve the sensitivity and selectivity of the electroanalytical probes, considering the electron mediator incorporation and the new conducting polymers development. The general procedures employed for the electrode modification and the operational characteristics of some electrochemical sensors are discussed.

In vivo determination of the monoamine neurotransmitters in rat brain by liquid chromatography with a thioctic acid/iridium oxide–palladium modified electrode

The fabrication and application of a electrochemical detector (ED) with the thioctic acid (TA)/iridium oxide (IrO2)–palladium (Pd) chemically modified electrode (CME) for liquid chromatography (LC) were described. The electrochemical behavior of dopamine (DA) and ascorbic acid (AA) at the TA/IrO2–Pd CME were investigated by differential pulse voltammetry (DPV). It was found that the CME could be permselective to DA cations and exile the AA anions, which could be used to determine the monoamine neurotransmitters and avoid the interference of AA in LC. In liquid chromatography with electrochemical detection (LC–ED), DA, norepinephrine (NE), 5-hydroxytryptamine (5-HT), epinephrine (E) and 3,4-dihydroxyphenylactic acid (DOPAC) were determined at the CME. The linear ranges of five analytes were over three orders magnitude and the limits of detection were 0.05 pmol for DA, 0.05 pmol for NE, 0.05 pmol for E, 0.10 pmol for 5-HT and 1.00 pmol for DOPAC. The application of this method coupled with microdialysis sampling for the in vivo determination of the monoamines in rat brain was also investigated.

Simultaneous determination of oxalate, thiosulfate, and thiocyanate in urine by ion-exclusion chromatography with electrochemical detection

A sensitive ion-exclusion chromatographic method has been developed for determination of oxalate, thiosulfate, and thiocyanate. The method is based on separation of these anions on a polymethacrylate-based, weakly acidic cation-exchange resin (TSKgel OApak-A) and detection by means of a glassy carbon (GC) electrode electrochemically modified with polyvinylpyridine (PVP), palladium, and iridium oxide (PVP/Pd/IrO2). The electrochemical behavior of oxalate, thiosulfate, and thiocyanate at this chemically modified electrode (CME) have been investigated by cyclic voltammetry. The results indicated that electrocatalytic oxidation of these anions by the electrode was efficient and that the sensitivity, stability, and lifetime of the electrode were relatively high. Combined with ion-exclusion chromatography the PVP/Pd/IrO2 electrode was used as the working electrode for amperometric detection of these anions. All linear ranges were over two orders of magnitude and detection limits, defined asS/N=3, were 9.0×10−7 mol L−1 for oxalate, 6.7×10−7 mol L−1 for thiosulfate, and 5.6×10−7 mol L−1 for thiocyanate. Correlation coefficients were all>0.998. Coupled with microdialysis sampling the method has been successfully applied to the determination of oxalate, thiosulfate, and thiocyanate in urine.

Amperometric determination of morphine on cobalt hexacyanoferrate modified electrode in rat brain microdialysates

The analysis of morphine in biological fluids is of vital interest in monitoring opiate abuse and in drug abuse research. In this paper, a cobalt hexacyanoferrate (CoHCF) chemically modified electrode (CME) was prepared. The electrochemical behavior of morphine at this modified electrode has been studied by cyclic voltammetry (CV). The results indicated that the modified electrode exhibited efficiently electrocatalytic oxidation for morphine with relatively high sensitivity and stability. The CoHCF CME was employed as the detector of high-performance liquid chromatography (HPLC). The peak current was linearly related to the morphine concentration in the range of 1.0×10 −6 M to 5.0×10 −4 M at +0.60 V (vs. Ag/AgCl) with a detection limit of 5.0×10 −7 M (S/N of 3). Typical intra-day reproducibility ( n=5) of 2.0% and inter-day reproducibility ( n=5) of 3.8% were obtained at the 2.0×10 −5 M level. This method was for the first time applied to study the pharmacokinetics of morphine in rat brain after an intravenous administration of morphine (25 mg kg −1).

Amperometric determination of glutathione and cysteine on a Pd-IrO(2) modified electrode with high performance liquid chromatography in rat brain microdialysate.

A Pd/IrO(2) co-electrodeposited glassy carbon electrode was prepared and the electrochemical behavior of glutathione (GSH) at this chemically modified electrode (CME) has been studied by cyclic voltammetry (CV). The results indicated that the modified electrode efficiently exhibited electrocatalytic oxidation for GSH with relatively high sensitivity, stability, and long-life. Coupled with high-performance liquid chromatography (HPLC), the Pd/IrO(2) modified electrode was utilized for the electrochemical detection (ECD) of the thiocompounds, glutathione and cysteine (Cys). The peak currents were linear with the substance concentrations in the range of 1.0 x 10(-5) mol L(-1) to 8.0 x 10(-4) mol L(-1) for GSH and 4.0 x 10(-6) mol L(-1) to 2.0 x 10(-4) mol L(-1) for Cys. The detection limits were 2.0 x 10(-6) mol L(-1) for GSH and 5.0 x 10(-7) mol L(-1) for Cys with S/N of 3. The method has been successfully applied to assess the contents of GSH and Cys in rat brain microdialysates.