Liquid Chromatographic Determination of Glutathione with Electrochemically Pretreated Glassy Carbon Electrode

Abstract

Simple electrochemical pretreatment of a glassy carbon electrode used as a working electrode in an electrochemical detector has been found to enhance the analytical capability of the detector for the determination of glutathione by lowering the required operating potential as well as by increasing the maximum oxidation current. The electrochemical pretreatment of the electrode was made in a 0.2 M phosphate buffer (KH₂PO₄-KOH, pH 6.5) at +1.9 V vs. Ag/AgCl for 2 min. The minimum detectable quantity of glutathione was found to be about 100 pg, when eluate from a reversed-phase column was amperometrically monitored by aid of the detector with the electrochemically pretreated glassy carbon electrode. Amount of glutathione in a rat lens was determined by the chromatographic method developed in this study.     

Electrochemical Determination of Dopamine Using a Poly(3,4-Ethylenedioxythiophene)-Reduced Graphene Oxide-Modified Glassy Carbon Electrode

Poly(3,4-ethylenedioxythiophene) was deposited on a reduced graphene oxide-decorated glassy carbon electrode through an electrochemical polymerization. The resulting glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was applied as an electrochemical biosensor for the determination of dopamine in the presence of ascorbic acid and uric acid. The material deposited on glassy carbon electrode was investigated in terms of morphology and structural analysis. The comparison of electrochemical behavior of the glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode with the glassy carbon electrode-graphene oxide, glassy carbon electrode-reduced graphene oxide, and glassy carbon electrode-poly(3,4-ethylenedioxythiophene) electrodes exhibited high electrocatalytic activity for dopamine detection. Electrochemical kinetic parameters of glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene), including the charge transfer coefficient α (0.49) and electron transfer rate constant k_s (1.04), were determined and discussed. The glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was studied for the determination of dopamine by differential pulse voltammetry and exhibited a linear range from 19.6 to 122.8?µM with a sensitivity of 3.27?µA?µM^?1?cm^?2 and a detection limit of 1.92?µM. The developed biosensor exhibited good selectivity toward dopamine with high reproducibility and stability.     

Electrochemical determination of L-cysteine using polyaniline/CuGeO3 nanowire modified electrode

The 10 wt % polyaniline/CuGeO₃ nanowire modified glassy carbon electrode has been used for the electrochemical determination of L-cysteine. The electrochemical behavior of L-cysteine at the 10 wt % polyaniline/CuGeO₃ nanowire modified glassy carbon electrode has been investigated. The intensities of the anodic cyclic voltammogram (CV) peaks of L-cysteine at the modified electrode increase linearly with the increase of the L-cysteine content in the range of 0.001–2 mM and scan rate ranging from 25 to 200 mV s^?1. 10 wt % polyaniline/CuGeO₃ nanowire modified glassy carbon electrode exhibits good reproducibility, stability and low detection limit of 1.7 and 0.44 μM for cvpl and cvp2, respectively. The polyaniline combined with the CuGeO₃ nanowires can improve the electrochemical detection ability of L-cysteine.     

Electrochemical behavior of tartaric acid at CuGeO3 nanowire modified glassy carbon electrode

The electrochemical behavior of tartaric acid at the CuGeO₃ nanowire modified glassy carbon electrode has been investigated by cyclic voltammetry (CV). The results show that two pairs of semireversible electrochemical peaks are observed and can be assigned to the process of oxidation–reduction and adsorption–desorption of tartaric acid at the modified glassy carbon electrode, respectively. The intensity of the CV peaks increases linearly with the increase of the content of tartaric acid in the range of 0.01–5 mM and scan rate ranging from 25–200 mV s^?1. CuGeO₃ nanowire modified glassy carbon electrode exhibits good detection ability for tartaric acid in neutral solution with the detection limit of 8.9 and 7.7 μM for cvp1 and cvp2, respectively, at a signal-to-noise ratio of 3. The CuGeO₃ nanowire modified glassy carbon electrode has good reproducibility and stability.     

An electrochemical biosensor for direct detection of DNA using polystyrene-g-soya oil-g-imidazole graft copolymer

A label-free electrochemical DNA biosensor was developed through the attachment of polystyrene-g-soya oil-g-imidazole graft copolymer (PS-PSyIm) onto modified graphene oxide (GO) electrodeposited on glassy carbon electrode (GC). GC/GO electrode was initially functionalised via electrochemical reduction of 4-nitrobenzene diazonium salt, followed by the electrochemical reduction of NO₂ to NH₂. Subsequent to the electrochemical deposition of gold nanoparticles on modified surface, the attachment of the PS-PSyIm graft copolymer on the resulting electrode was achieved. The interaction of PS-PSyIm with DNA at the bare glassy carbon electrode was studied by cyclic voltammetry technique, and it was found that interaction predominantly takes place through intercalation mode. The selectivity of developed DNA biosensor was also explored by DPV on the basis of considering hybridisation event with non-complementary, one-base mismatched DNA and complementary target DNA sequence. Large decrease in the peak current was found upon the addition of complementary target DNA. The sensitivity of the developed DNA biosensor was also investigated, and detection limit was found to be 1.20 nmol L^?1.     

Electrocatalytic oxidation and flow-injection determination of sulfur amino acids on a glassy carbon electrode modified by a nickel(II) polytetrasulfophthalocyanine film

The electrochemical oxidation of sulfur amino acids, i.e., cysteine, cystine, and methionine, is studied on a glassy carbon electrode modified by a film of nickel(II) polytetrasulfophthalocyanine (poly-NiTsPc). Poly-NiTsPc demonstrates a selective mediator activity in the oxidation of sulfur amino acids, depending on the pH of solution. The proper conditions for fabricating a polymer film on the surface of glassy carbon are found and the conditions of registering the maximal electrocatalytic effect on the modified electrode are determined. A procedure is proposed for the voltammetric determination and amperometric detection of cysteine, cystine, and methionine on an electrode coated by a poly-NiTsPc film under the conditions of flow-injection analysis (FIA). The linear relation of the electrocatalytic response of a composite electrode to amino acid concentration is observed to the level n × 10^?6 M in the static mode and n × 10^?9 M under FIA conditions.     

Electrochemical and impedance spectroscopy studies of various diazonium salts on a glassy carbon electrode

Abstract  

The derivatization of a glassy carbon electrode surface was achieved with and without electrochemical reduction of various diazonium salts in acetonitrile solutions. The surfaces were characterized, before and after their attachment, by cyclic voltammetry and electrochemical impedance spectroscopy to evidence the formation of a coating on the carbon surface. The results were indicative of the presence of substituted phenyl groups on the investigated surface. Also, the effects of diazonium thin films at the surface of a glassy carbon electrode, modification time, and salt concentration on their electrochemical responses in the presence of the Fe(CN)₆^3−/4− probe were investigated. Electrochemical impedance measurements indicated that the kinetics of electron transfer is slowed down when the time and the concentration used to modify the glassy carbon electrode are increased. We therefore modified a glassy carbon surface via its derivatization with and without electrochemical reduction of various diazonium salts in acetonitrile solution.     

Electrochemical Determination of Hydrogen Peroxide Using a Glassy Carbon Electrode Modified with Three-Dimensional Copper Hydroxide Nanosupercages and Electrochemically Reduced Graphene Oxide

Three-dimensional copper hydroxide nanosupercages and electrochemically reduced graphene oxide were used to modify the glassy carbon electrode for the selective determination of hydrogen peroxide. The morphology and electrochemistry properties of copper hydroxide nanosupercage/electrochemically reduced graphene oxide/glassy carbon electrode were characterized using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectra, Raman spectra, cyclic voltammetry, and electrochemical impedance spectroscopy. The resulting copper hydroxide nanosupercage/electrochemically reduced graphene oxide/glassy carbon electrode showed favorable performance for the electrocatalytic reduction of hydrogen peroxide. The amperometric current–time curve of the electrochemical sensor exhibited a wide linear range from 0.5 to 1030?µM with a limit of detection of 0.23?µM at a signal-to-noise ratio of three. Moreover, the sensor provided favorable selectivity, reproducibility, and stability and was used for the determination of H₂O₂ in tap water.     

Electrochemical preparation of a novel type of C-dots/ZrO2 nanocomposite onto glassy carbon electrode for detection of organophosphorus pesticide

A selective, sensitive novel electrochemical sensor for detection of methyl parathion on the preparation of a carbon dots (C-dots)/ZrO₂ nanocomposite was developed. The C-dots/ZrO₂ nanocomposite was fabricated using electrochemical deposition onto a glassy carbon electrode and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and cyclic voltammetry. The optimum parameters such as effect of pH, accumulation time, accumulation potential, scan rate, effect of amount of C-dots and effect of amount of ZrO₂ were investigated. The C-dots/ZrO₂ modified glassy carbon electrode allowed rapid, selective determination of methyl parathion in rice samples by adsorptive stripping voltammetry. The stripping response was highly linear over the methyl parathion concentrations ranging from 0.2 ng mL^?1 to 48 ng mL^?1, with a detection limit of 0.056 ng mL^?1. This novel electrochemical nanocomposite-based electrochemical sensor was successfully applied for the detection of methyl parathion in rice samples.     

Ag Doped Titanium Dioxide Nanocomposite‐modified Glassy Carbon Electrode as Electrochemical Interface for Catechol Sensing

The electrochemical sensing of catechol (CC) on a glassy carbon electrode modified with the ionothermal assisted synthesis of Ag doped TiO₂ a nanoparticle has been successfully demonstrated for the first time.Ag doped TiO₂ nanoparticles composite modified glassy carbon electrode exhibits higher electrocatalytic activity towards oxidation of catechol than glassy carbon electrode itself. The modified electrode also exhibits high selectivity towards this analyte in the presence of some of the metal ions and some of the biological compounds. Linear ranges and the limit of detections with the above electrode are 1–15 µM and 0.0249 µM respectively. The optimized protocol has been utilized for monitoring the catechol in some of the natural samples like apple juice and green tea and in industrial effluents.     

Electrochemical deposition of platinum nanoparticles in multiwalled carbon nanotube–Nafion composite for methanol electrooxidation

Platinum nanoparticles were successfully deposited within a multiwalled carbon nanotube (MWCNT)–Nafion matrix by a cyclic voltammetry method. A Pt(IV) complex was reduced to platinum nanoparticles on the surface of MWCNTs. The resulting Pt nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The Pt–MWCNT–Nafion nanocomposite film-modified glassy carbon electrode had a sharp hydrogen desorption peak at about −0.2 V vs. Ag/AgCl (3 M) in a solution of 0.5 M H₂SO₄, which is directly related to the electrochemical activity of the Pt nanoparticles presented on the surface of MWCNTs. The electrocatalytic properties of the Pt–MWCNT–Nafion nanocomposite-modified glassy carbon electrode for methanol electrooxidation were investigated by cyclic voltammetry in a 2 M CH₃OH + 1 M H₂SO₄ solution. In comparison with the Pt-coated glassy carbon electrode and the Pt–Nafion modified glassy carbon electrode, the Pt–MWCNT–Nafion-modified electrode had excellent electrocatalytic activity toward methanol electrooxidation. The stability of the Pt–MWCNT–Nafion nanocomposite-modified electrode had also been evaluated.     

Investigations on Bioanalytical Chemistry Part I. On Differential Pulse Voltammetry of Bilirubin

Abstract

The electrochemical behaviour of the bilirubin in many kinds of supporting electrolytes on a glassy carbon electrode (GCE) and a hanging mercury drop electrode (HMDE) was investigated by means of anodic or cathodic differential pulse voltammetry. The influences of different methods of pre-treatment of the glassy carbon electrode was also discussed. In Na₂B₄.O₇-KH₂PO₄ buffer solution, the linear range was 2×10^?9-1×10^?9 mol/l and the detection limit was 3.3×10^?9 mol/l by anodic differential pulse voltammetry at GCE. A linear relationship holds between the peak current and the concentration of bilirubin in a concentration range of 1×10^?9-4×10^?7 mol/l with good precision and accuracy, and the limit of detection was 2×10^?10 mol/l, when cathodic differential pulse adsorption voltammetry at HMDE was used.     

HPLC Urinary Organic Acid Profiling: Role of the Ultraviolet and Amperometric Detectors

Abstract

The profiling of urinary organic acids is an important aspect of the diagnosis of inborn metabolic disorders. The carboxylic acids of interest may contain additional functional moities such as phenyl, hydroxyl, oxo, etc. The state-of-the-art method of organic acid analysis is by GC/MS. Prior to GC/MS analysis, the carboxylic acids must be isolated from urine by extraction or ion exchange chromatography and made volatile by derivatization. This is a lengthy procedure that does not lend itself to rapid analysis. We have developed a rapid procedure for the profiling of urinary α, B-unsaturated, aromatic and α-ketocarboxylic acids.

Urine containing an internal standard, 3-hydroxy-4-methoxy-benzyl alcohol, is filtered through a 0.3 um Millipore filter and injected on to an HPX-87 organic acid HPLC column (Bio-Rad). The mobile phase, 4.5 mN H₂SO₄, is passed through the column at 0.8 ml/min. Detection is effected by an UV detector at 200 nm in series but upstream from an electrochemical detector with a glassy carbon working electrode at +1.15V vs. an Ag/AgCl reference electrode. At this electrode potential, phenolic, methoxyphenyl, eneolic and α-ketocarboxylic acids are oxidized and can be electrochemically detected with a glassy carbon electrode.     

High-performance electrochemical sensor based on electrodeposited iron oxide nanoparticle: catecholamine as analytical probe

In this paper, we report the synthesis and electrocatalytic activity of electrodeposited Fe₂O₃ nanoparticles modified on a glassy carbon electrode as highly sensitive sensors for determination of catecholamines. Results showed that the Fe₂O₃ nanoparticles on a glassy carbon electrode exhibit excellent catalytic activity toward catecholamines oxidation, including levodopa, dopamine, and epinephrine, resulting in a marked lowering in the peak potential and considerable improvement of the peak current as compared to the electrochemical activity at the bare glassy carbon electrode. The electrochemical characterizations of catecholamines were performed using cyclic voltammetry, chronoamperometry, and differential pulse voltammetry techniques. The electrocatalytic currents increase linearly with the levodopa, dopamine, and epinephrine concentrations in the ranges of 0.0625–1000, 0.25–1500, and 0.125–1000 µM, respectively, and the detection limits (3σ) were 24 ± 2, 14 ± 2, and 12 ± 2 nM, respectively.     

Highly Sensitive Electrochemical Sensor for Determination of Vitamin D in Mixtures of Water‐Ethanol

This paper describes the electrochemical determination of vitamin D₂ (ergocalciferol) and D₃ (cholecalciferol) in mixed organic/water solvent, using a glassy carbon electrode (GCE). The mixing ratio of organic/water solvent has an important influence on the electrocatalytic response of D vitamins on the surface of the glassy carbon electrode. Well‐defined peaks for Vitamin D₂ and D₃ were observed in a 40 % ethanol/60 % water solution with lithium perchlorate as the support electrolyte. This study demonstrated that the glassy carbon electrode is highly sensitive for the determination of vitamin D₂ and D₃, with a limit of detection of 0.13 and 0.118 µmol L^?1, respectively. No significant interference was seen for vitamins A, E and K in the detection of vitamin D.     

Glassy carbon and boron doped glassy carbon electrodes for voltammetric determination of linuron herbicide in the selected samples

In this study the application of home-made unmodified (GC) and bulk modified boron doped glassy carbon (GCB) electrodes for the voltammetric determination of the linuron was investigated. The electrodes were synthesized with a moderate temperature treatment (1000°C). Obtained results were compared with the electrochemical determination of the linuron using a commercial glassy carbon electrode (GC-Metrohm). The peak potential (E _p ) of linuron oxidation in 0.1 mol dm⁻³ H₂SO₄ as electrolyte was similar for all applied electrodes: 1.31, 1.34 and 1.28 V for GCB, GC and GC-Metrohm electrodes, respectively. Potential of linuron oxidation and current density depend on the pH of supporting electrolyte. Applying GCB and GC-Metrohm electrodes the most intensive electrochemical response for linuron was obtained in strongly acidic solution (0.1 mol dm⁻³ H₂SO₄). Applying the boron doped glassy carbon electrode the broadest linear range (0.005–0.1 μmol cm⁻³) for the linuron determination was obtained. The results of voltammetric determination of the linuron in spiked water samples showed good correlation between added and found amounts of linuron and also are in good agreement with the results obtained by HPLC-UV method. This appears to be the first application of a boron doped glassy carbon electrode for voltammetric determination of the environmental important compounds.      

Determination of Apomorphine in Tablets Using High Performance Liquid Chromatography with Electrochemical Detection

Abstract

A rapid and selective method using high performance liquid chromatography with electrochemical detection is described for the determination of apomorphine in tablets. Tablet mixes were dissolved in a standard volume of mobile phase containing the internal standard, N-n-propylnorapomorphine. Separation was achieved on a μ-phenyl column using methanol-acetonitrile-0.05M KH₂PO₄ (5:15:80) as mobile phase. The eluted compounds were detected with a sandwich-type electrochemical detector employing a glassy carbon working electrode and operated at 0.5V. Satisfactory accuracy and precision were obtained during analyses of tablets containing apomorphine.     

Electrochemical synthesis and study of coordination compounds part 1: tin(II) catechol complexes

The electrochemical synthesis of tin(II) complexes of catechols, Sn(O₂Ar) (1a–9a), have carried out using tin metal as a sacrificial anode in acetonitrile, in the presence of catechol derivatives. The cyclic voltammetric characteristics of the synthesized complexes Sn(O₂Ar) (1a–9a) have been studied at glassy carbon electrode in dichloromethane. Anodic oxidation of Sn(O₂Ar) produces a single wave which shows irreversibility. Also, the electronic effects of ligands on the redox potential of complexes 1a–9a have been investigated. The synthesis of Sn(O₂Ar) species in high yields and purity has been successfully performed in an undivided cell using constant current conditions.     

An amperometric biosensor using toluidine blue as an electron transfer mediator intercalated in α-zirconium phosphate-modified horseradish peroxidase immobilization matrix

A novel H₂O₂ biosensor was constructed employing α-zirconium phosphate as a new support substrate to hold an electron shuttle toluidine blue between a glassy carbon electrode and horseradish peroxidase. Toluidine blue was intercalated into α-zirconium phosphate-modified horseradish peroxidase immobilization matrix cross-linked on a glassy carbon electrode surface via bovine serum albumin-glutaraldehyde. This co-immobilization matrix of the mediator and the enzyme was formed from the α-zirconium phosphate (α-ZrP)-toluidine blue (TB) inclusion colloid in which horseradish peroxidase (HRP) was dissolved. Intercalation of TB in layered α-ZrP was investigated by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and electrochemical measurements. TB immobilized in this way underwent a quasi-reversible electrochemical redox reaction at the electrode. Cyclic voltammetry and amperometric measurements demonstrated good stability and efficiently-shuttled electrons between HRP and the electrode. The sensor responded rapidly to H₂O₂ with a detection limit of 3.0 × 10^–7 mol/L.     

One-step electrochemical synthesis of Pt–CeO2 composite thin films on a glassy carbon electrode

A Pt–CeO₂ composite thin film was prepared on a glassy carbon electrode by one-step electrochemical deposition technique. The film was constructed of Pt particles well dispersed and embedded in a porous CeO₂ substrate. The prepared Pt–CeO₂/GC electrode showed a better catalytic performance toward methanol electrooxidation compared with the bulk Pt electrode.