磷钼钒杂多酸-聚邻苯二胺修饰碳糊电极示差脉冲溶出伏安法测定对苯二酚和邻苯二酚

在由磷钼钒杂多酸和邻苯二胺组成的支持电解质中,以0.100V.s-1扫速在碳糊电极上,于0.800～-0.800V范围内循环扫描20周后,制得磷钼钒杂多酸-聚邻苯二胺修饰碳糊电极。循环伏安法研究发现:对苯二酚(HQ)和邻苯二酚(CC)在该修饰电极上均出现了一对氧化还原峰;示差脉冲溶出伏安法研究发现:HQ和CC分别在0.140V和0.288V处出现二次微分溶出峰,两峰电位差为0.148V。HQ和CC的线性范围均为1.50×10-7～7.50×10-4 mol.L-1,检出限(3S/N)均为6.80×10-8 mol.L-1。据此提出了示差脉冲溶出伏安法测定模拟水样中HQ和CC,测得回收率在94.0%～106.0%之间。     

Direct electrochemistry behavior of cytochrome c/L-cysteine modified electrode and its electrocatalytic oxidation to nitric oxide

Cytochrome c (Cyt c) was successfully immobilized on L-cysteine modified gold electrode by multicyclic voltammetry method. The electrochemical behavior of Cyt c on the L-cysteine modified electrode was explored. In 0.10 M, pH 7.0 phosphate buffer solution (PBS), Cyt c showed a quasi-reversible electrochemical redox behavior with E(pc)=0.180 V, E(pa)=0.208 V (versus Ag/AgCl). The Cyt c/L-cysteine modified electrode gave an excellent electrocatalytic activity towards the oxidation of nitric oxide, and the catalysis currents were proportional to the nitric oxide concentration in the range of 7.0 x 10(-7) to 1.0 x 10(-5) M, the linear regression equation is I (microA)=-0.124-0.003 C(NO) (microM), with a correlation coefficient 0.996, The detection limit was 3.0 x 10(-7) M (times the ratio of signal to noise, S/N=3).     

Electroregenerable anion-exchange resin with triiodide carbon paste electrode for the voltammetric determination of adrenaline

An electroregenerable carbon paste electrode modified with triiodide ions immobilized in an anion-exchange resin (Lewatit M500) is proposed for the determination of adrenaline in pharmaceutical products by differential-pulse voltammetry (DPV). Adrenaline was chemically converted into adrenochrome by the I3- ions at the electrode surface. The electrochemical reduction back to adrenaline was obtained at a potential of -0.16 V vs. Ag/AgCl (3 mol l(-1) KCl). A 20% decrease of the initial analytical signal was observed after 350-400 determinations; the carbon paste electrode was 100% electroregenerated at a fixed potential of +0.65 V vs. Ag/AgCl (3 mol l(-1) KCl) in 0.1 mol l(-1) KI solution for 20 min. The differential-pulse voltammograms were obtained by applying a sweep potential between 0.0 and -0.34 V, following the adrenochrome reduction at -0.16 V. Under the optimum conditions established, such as pH 6.0; scan rate 20 mV s(-1) and pulse amplitude 50 mV, the calibration curve was linear from 2.0 x 10(-5) to 3.1 x 10(-4) mol l(-1) adrenaline with a detection limit of 3.9 x 10(-6) mol l(-1). The recovery of adrenaline ranged from 99.8 to 103.1% and the RSD was 2.6% for the solution containing 1.0 x 10(-4) mol l(-1) adrenaline (n = 10). The results obtained for adrenaline in pharmaceutical samples using the proposed carbon paste electrode are in agreement with those obtained using a pharmacopoeial procedure at the 95% confidence level.     

Electrochemical behaviour of sertraline at a hanging mercury drop electrode and its determination in pharmaceutical products

The electrochemical behaviour of sertraline at a hanging mercury drop electrode (HMDE) was described. Different voltammetric techniques, such as cyclic, linear sweep, differential pulse and square wave voltammetry, were used. Voltammograms were obtained at different pH values with a Britton-Robinson buffer solution used as supporting electrolyte. The best results were found by square wave voltammetry with electrodeposition at alkaline pH using a borate buffer with a pH = 8.2 for the samples, containing 12% (v/v) methanol. Under optimised conditions, a linear relationship between 2.33 x 10(-7) and 3.15 x 10(-6) M of sertraline with a limit of detection of 1.98 x 10(-7) M was obtained. The electrochemical method developed was applied to the determination of sertraline in pharmaceutical formulations. Recoveries were close to 100%, thus proving efficacy of the proposed method for the quantification of sertraline in commercial samples.     

Voltammetric determination of sinomenine in biological fluid using a glassy carbon electrode modified by a composite film of polycysteic acid and carbon nanotubes

Polycysteic acid based electrochemical oxidation of L-cysteine (CySH) and carbon nanotubes (CNTs) formed a composite thin film material at a glassy carbon electrode (GCE) that was used a novel modifier for electroanalytical determination of sinomenine which is used for rheumatoid arthritis treatment. The determination of sinomenine at the composite modified electrode was studied by differential pulse voltammetry (DPV). The peak current obtained at + 0.632 V (vs SCE) from DPV was linearly dependent on the sinomenine concentration in the range of 1.0 x 10(-7) to 6.0 x 10(-5) M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N = 3) was 5.0 x 10(-8) M. The electrochemical reaction mechanism of sinomenine was also discussed. This new method was then applied to the high-throughput determination of sinomenine in human serum samples with satisfactory results. This polycysteic acid/CNTs composite film may be considered to be a promising, low-cost, durable, and biocompatible material for the modification of sensors in applications to pharmaceutical and biomedical analysis.     

Determination of trace levels of diosmin in a pharmaceutical preparation by adsorptive stripping voltammetry at a glassy carbon electrode.

A systematic study on the electrochemical behavior of diosmin in Britton-Robinson buffer (pH 2.0-10.0) at a glassy carbon electrode (GCE) was made. The oxidation process of the drug was found to be quasi-reversible with an adsorption-controlled step. The adsorption stripping response was evaluated with respect to various experimental conditions, such as the pH of the supporting electrolyte, the accumulation potential and the accumulation time. The observed anodic peak current at +0.73 V vs. Ag/AgCl reference electrode increased linearly over two orders of magnitude from 5.0x10(-8) M to 9.0x10(-6) M. A limit of detection down to 3.5x10(-8) M of diosmin at the GCE was achieved with a mean recovery of 97+/-2.1%. Based on the electrochemical data, an open-circuit accumulation step in a stirred sample solution of BR at pH 3.0 was developed. The proposed method was successfully applied to the determination of the drug in pharmaceutical formulations. The results compared favorably with the data obtained via spectrophotometric and HPLC methods.     

Voltammetric determination of terbinafine in biological fluid at glassy carbon electrode modified by cysteic acid/carbon nanotubes composite film

The electrochemical oxidation of L-cysteine (CySH) in presence of carbon nanotubes (CNTs) formed a composite film at a glassy carbon electrode (GCE) as a novel modifier for directly electroanalytical determination of terbinafine without sample pretreatment in biological fluid. The determination of terbinafine at the modified electrode with strongly accumulation was studied by differential pulse voltammetry (DPV). The peak current obtained at +1.156 V (vs. SCE) from DPV was linearly dependent on the terbinafine concentration in the range of 8.0 x 10(-8)-5.0 x 10(-5 )M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N=3) was 2.5 x 10(-8 )M. The low-cost modified electrode showed good sensitivity, selectivity, and stability. This developed method had been applied to the direct determination of terbinafine in human serum samples with satisfactory results. It is hopeful that the modified electrode will be applied for the medically clinical test and the pharmacokinetics in future.     

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 1.0x10(-6) M to 5.0x10(-4) M at +0.60 V (vs. Ag/AgCl) with a detection limit of 5.0x10(-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 2.0x10(-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 mgkg(-1)).     

Direct electrochemical behavior of cytochrome c on DNA-modified glassy carbon electrode and its application to cytochrome c biosensor.

DNA was immobilized on glassy carbon electrodes to fabricate DNA-modified electrodes. The direct electron transfer of horse heart cytochrome c on DNA-modified glassy carbon electrode was achieved. A pair of well-defined redox peaks of cytochrome c appeared at Epc = -0.017 V and Epa = 0.009 V (vs. Ag/AgCl) in 10 mM phosphate buffer solution (pH 7.0) at a scan rate of 50 mV/s. The electron transfer coefficient (alpha) and the standard rate constant of the surface reaction (Ks) of cytochrome c on DNA-modified electrodes could be estimated to be 0.87 and 34.52 s(-1), respectively. The DNA-modified glassy carbon electrode could be applied to detect cytochrome c by means of differential pulse voltammetry (DPV). The cathodic peak current was proportional to the quantity of cytochrome c in the range of 4.0 x 10(-6) M to 1.2 x 10(-5) M. The correlation coefficient is 0.996, and with the detection limit was 1.0 x 10(-6) M (three times the ratio of signal to noise, S/N = 3).     

Adsorptive stripping voltammetry determination of molybdenum(VI) in water and soil

A differential pulse stripping voltammetry method for the trace determination of molybdenum(VI) in water and soil has been developed. In 0.048M oxalic acid and 6 x 10(-5)M Toluidine Blue (pH 1.8) solution, Mo(V), the reduction product of Mo(VI) in the sample solution, can form a ternary complex, which can be concentrated by adsorption on a static mercury drop electrode at -0.1 V (vs. Ag/AgCl). The adsorbed complex gives a well-defined cathodic stripping current peak at -0.30 V, which can be used for determining Mo(VI) in the range 5 x 10(-10)-7 x 10(-9)M, with a detection limit of 1 x 10(-10)M (4 min accumulation). The method is also selective. Most of the common ions do not interfere but Sn(IV) and large amounts of Cu(2+), Ag(+) and Au(3+) affect the determination.     

Amperometric determination of urea using an NADH-dependent coupled enzyme

Enzyme electrodes for the amperometric measurement of urea were prepared by co-immobilizing l-glutamate dehydrogenase and urease onto an Immobilon-AV affinity membrane with attachment to a glassy carbon electrode. Reduced nicotinamide adenine dinucleotide (NADH) was used as the electroactive species. The electrochemical oxidation of NADH was monitored at +1.0 V vs. Ag/AgCl. The enzyme immobilized electrode was linear over the range of 2.0 x 10(-5) to 2 x 10(-4)M. The response time of the electrode was 3 min and the optimum pH of enzyme immobilized membrane was pH 7.4-7.6 (Dulbecco's buffer solution). It was stable for at least two weeks and 50 assays. There were no interferences from other physiological material, except for high levels of ascorbic acid.     

Voltammetric determination of niclosamide at a glassy carbon electrode

A very sensitive and selective procedure was developed for the determination of niclosamide based on square-wave voltammetry at a glassy carbon electrode. Cyclic voltammetry was used to investigate the electrochemical reduction of niclosamide at a glassy carbon electrode. Niclosamide was first irreversibly reduced from NO2 to NHOH at -0.659 V in aqueous buffer solution of pH 8.5. Reversible and well defined peaks at -0.164 V and -0.195 V (vs. Ag/AgCl) were obtained that are responsible for two electron peaks between NHOH and NO. Following optimisation of the voltammetric parameters, pH and reproducibility, a linear calibration curve over the range 5 x 10(-8)-1 x 10(-6) mol dm(-3) was achieved. The detection limit was found to be 2.05 x 10(-8) mol dm(-3) niclosamide. For eight successive determinations of 5 x 10(-7) mol dm(-3) niclosamide, a relative standard deviation of 2.4% was obtained. This voltammetric method was applied to the direct determination of niclosamide in tablets. The results of the analysis suggest that the proposed method has promise for the routine determination of niclosamide in the products examined.     

Electrocatalytic response of dopamine at a metallothioneins self-assembled gold electrode.

The metallothioneins (MT) self-assembled monolayer modified gold electrode (MT/Au) is demonstrated to catalyze the electrochemical response of dopamine (DA) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant (k(s)) is 6.97 x 10(-3) cm s(-1) (20 degrees C) at the self-assembled electrode. The electrode reaction is a quasi-reversible process. The oxidation peak of DA can be used to determine the concentration of DA. The peak current and the concentration of DA follow a linear relationship in the range of 2.0 x 10(-5) M to 8.0 x 10(-4) M. The detection limit is 6.0 x 10-6 M. By ac impedance spectroscopy, the apparent electron transfer rate constant (k(app)) of Fe(CN)6(3-)/Fe(CN)6(4-) at the MT/Au electrode was obtained as 2.0 x 10(-5) cm s(-1). The MT/Au was characterized with grazing angle FT-IR spectroscopy and contact angle goniometry.     

Electrochemical properties of myoglobin deposited on multi-walled carbon nanotube/ciprofloxacin film

We report the direct electrochemical and electrocatalytic properties of myoglobin (MB) on a multi-walled carbon nanotube/ciprofloxacin (MWCNT/CF) film-modified electrode. A highly homogeneous MWCNT thin-film was prepared on an electrode surface using ciprofloxacin (CF) as a dispersing agent. MB was then electrochemically deposited onto the MWCNT/CF-modified electrode. The MB/MWCNT/CF film was characterized by scanning electron microscopy and UV-visible spectroscopy (UV-vis). UV-vis spectra confirmed that MB retained its original state on the MWCNT/CF film. Direct electrochemical properties of MB on the MWCNT/CF film were investigated by cyclic voltammetry. The formal potential and electron transfer rate constant were evaluated in pH 7.2 buffer solution as -0.327V and 300s(-1), respectively. In addition, the MB/MWCNT/CF-modified electrode showed excellent electrocatalytic properties for the reduction of hydrogen peroxide (H(2)O(2)). The MB/MWCNT/CF-modified electrode was used for the detection of H(2)O(2) at concentrations from 1×10(-6)M to 7×10(-4)M in pH 7.2 buffer solution. Overall, the MB/MWCNT/CF-modified electrode was very stable and has potential for development as a H(2)O(2) sensor.     

Electrochemical study of the antineoplastic agent etoposide at carbon paste electrode and its determination in spiked human serum by differential pulse voltammetry

The electrochemical oxidation of the antineoplastic agent etoposide was studied at carbon paste electrode in Britton-Robinson buffer solutions over the pH range 2.0-10.0 using cyclic, linear sweep and differential pulse voltammetry. Oxidation of the drug was effected in a single reversible, diffusion-controlled step within the pH range 2.0-4.0, a second oxidation process was produced above pH 4.0. Using differential pulse voltammetry (DPV), the drug yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 3.0 at 0.500 V (vs. Ag/AgCl) on carbon paste electrode. This process could be used to determine etoposide concentrations in the range 2.5 x 10(-7) to 2.5 x 10(-5) M with a detection limit of 1.0 x 10(-7) M. The method was successfully applied to the determination of the drug in spiked human serum.     

Adsorptive and electrochemical behaviors of estradiol valerate at a mercury electrode

It was found that estradiol valerate could be adsorbed at a mercury electrode under open circuit. The adsorptive and electrochemical behaviors of estradiol valerate on a static mercury electrode were investigated by cyclic voltammetry, linear scan voltammetry and chronocoulometry. Based on this, a sensitive and selective adsorptive stripping square-wave voltammetric method was developed for the determination of estradiol valerate based on the optimization of solution conditions and electrochemical parameters. It was found that in a Britton-Robinson buffer solution containing 18% alcohol (pH 9.5), estradiol valerate gave a sensitive reductive peak at potential -1.29 V (vs. SCE) and the peak current was linear with the concentration of estradiol valerate in the range 2.0 x 10(-8)-2.5 x 10(-6) mol L-1. The detection limit was 1.1 x 10(-8) mol L-1. The interference of some common steroid estrogens was examined and it was found that they did not interfere in the determination of estradiol valerate in the present system.     

Sensitive detection of trifluoperazine using a poly-ABSA/SWNTs film-modified glassy carbon electrode

A poly-ABSA/SWNTs composite-modified electrode was fabricated by electropolymerizing aminobenzene sulphonic acid (ABSA) on the surface of glassy carbon electrode (GCE) modified with single-wall carbon nanotubes (SWNTs). SWNTs provide a 3D porous and conductive network for the polymer immobilization. The nanocomposite film was characterized by scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS). The results indicated that this composite-modified electrode had strong electrocatalytic activity toward the oxidation of trifluoperazine (TFP). TFP could effectively accumulate on the modified electrode and generate a sensitive anodic peak at 0.72V (versus SCE) in pH 6.1 phosphate buffer solution. Under the selected conditions, the anodic peak current of TFP was linear with its concentration within the range from 1.0x10(-7) to 1.0x10(-5)molL(-1) and 1.0x10(-5) to 1.0x10(-4)molL(-1), and the detection limit was 1.0x10(-9)molL(-1) (S/N=3). This method was successfully applied to the detection of trifluoperazine in drug samples and the recovery was satisfactory. In comparison with the SWNTs/GCE or poly-ABSA/GCE prepared in the similar way, this composite-modified electrode exhibited better catalytic activity.     

Mechanically immobilized nickel aquapentacyanoferrate modified electrode as an amperometric sensor for the determination of BHA

Nickel aquapentacyanoferrate (NAPCF), a novel transition metal complex has been prepared and its ability to act as an electrocatalyst for BHA oxidation has been demonstrated. The cyclic voltammetric behaviour of the NAPCF modified electrode prepared by mechanical immobilization on the graphite electrode was well defined. A pair of redox peaks corresponding to the electrochemical behaviour of the NAPCF was observed at 0.35 V and 0.31 V, corresponding to the anodic and cathodic peaks respectively, with a formal potential of 0.33 V. The NAPCF modified electrode favoured electrocatalytic oxidation of BHA to occur at a greatly minimized overpotential of 0.48 V. Experiments were performed to characterize the electrode as an amperometric sensor for the determination of BHA. The anodic peak current was linearly related to BHA concentration in the range of 6.24x10(-7) M to 2.19x10(-4) M with a detection limit of 2.49x10(-7) M and a correlation coefficient of 0.9979. Amperometry in stirred solution exhibited quick and sensitive response to BHA, showing the possible application of the modified electrode in flow system analysis. The modified electrode retained its initial response for more than 2 months when stored in supporting electrolyte, owing to the chemical and mechanical stability of the NAPCF mediator. This modified electrode was also quite effective in the determination of BHA in commercial samples.     

Enhanced electrochemical detection of ketorolac tromethamine at polypyrrole modified glassy carbon electrode.

A glassy carbon electrode modified with a coating of polypyrrole (Ppy) exhibited an attractive performance for the detection and determination of a non-steroidal and non-narcotic analgesic compound, ketorolac tromethamine (KT). Cyclic voltammetry, differential pulse and square wave voltammetry were used in a combined way to identify the electrochemical characteristics and to optimize the conditions for detection. For calibrating and estimating KT, square-wave voltammetry was mainly used. The drug shows a well-defined peak at -1.40 V vs. Ag/AgCl in the acetate buffer (pH 5.5). The existence of Ppy on the surface of the electrode gives higher electrochemical active sites at the electrode for the detection of KT and preconcentrate KT by adsorption. The square-wave stripping voltammetric response depends on the excitation signal and the accumulation time. The calibration curve is linear in the range 1 x 10(-11) to 1 x 10(-7) M with a detection limit of 1.0 x 10(-12) M. Applicability to serum samples was also demonstrated. A detection limit of 1.0 ng ml for serum was observed. Square-wave voltammetry shows superior performance over UV spectroscopy and other techniques.     

Determination of physiological thiols by electrochemical detection with piazselenole and its application in rat breast cancer cells 4T-1

Glutathione (GSH), the most abundant cellular thiol, has been shown to play an important role in maintaining cellular redox equilibrium that is pivotal for cell growth and function. In the present paper a novel electrochemical probe of piazselenole containing a Se-N bond was well developed for the determination of GSH. The cyclic voltammogram of piazselenole scanned at 100 mV/s displayed an irreversible reduction peak at -0.106 V (vs Ag/AgCl electrode) and a significant peak current decrease could be further provoked with the addition of GSH into piazselenole solution. On the basis of the peak current decrease of piazselenole recorded by differential pulse voltammetry with the increase of GSH concentration, a working curve was constructed for GSH determination in the range of 5.0 x 10(-10) approximately 2.2 x 10(-8) M with the linear regression equation as DeltaiP (10(-6)A) = 0.0952 + 0.4287 x CGSH (10(-8) M) and the detection limit (3sigma) as 83 pM. The proposed method was satisfactorily applied to the extracts of rat breast cancer cells 4T-1 for intracellular thiols detection.