Voltammetry determination of trace manganese with pretreatment glassy carbon electrode by linear sweep voltammetry

This paper described the determination of trace manganese using linear sweep voltammetry at a pretreatment glassy carbon electrode. The glassy carbon electrode pretreated by electrochemical method in the 0.1 mol l⁻¹ NaOH solution greatly improved the electrode responsibility in the determination of manganese(II). The barrier to the detection of low manganese concentration was overcome by means of autocatalytic effect of manganese oxide deposited on the electrode in advance. Under the optimum experiments condition (0.04 mol l⁻¹ NH₃-NH₄Cl buffer solution, pH 9.0), the linear range was 4×10⁻⁸ to 1×l0⁻⁶ mol l⁻¹ Mn(II) for linear sweep voltammetry and 1×10⁻⁹ to 4×10⁻⁸ mol l⁻¹ Mn(II) for convolution voltammetry. The relative standard deviation for 2×10⁻⁸ mol l⁻¹ Mn(II) is 3.4%. The proposed method is simple, rapid, sensitive and selective. It had been applied to the determination of trace manganese in samples with satisfactory results.     

Simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations by differential-pulse voltammetry using a glassy carbon electrode

A simple, rapid and accurate method for the simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations has been developed. Peak currents were measured with a glassy carbon electrode at +0.350, +0.618 and +1.425 V versus a saturated calomel electrode for ascorbic acid, paracetamol and caffeine, respectively. Perchloric acid (0.1 M) - methanol (1 + 1) was used both as a solvent and supporting electrolyte. The optimum modulation amplitude, pulse repeat time and scan rate of the polarographic analyser were found to be 50 mV, 0.5 s and 5 mV s-1, respectively and the linear calibration ranges for ascorbic acid, caffeine and paracetamol were 0-35, 0-50, and 0-55 micrograms ml-1, respectively. The relative standard deviations for 9.30 micrograms ml-1 of ascorbic acid, 8.50 micrograms ml-1 of caffeine and 7.30 micrograms ml-1 of paracetamol were 1.3, 2.5 and 0.7%, respectively. Results are reported for several commercially available drugs.     

Simultaneous determination of three fluoroquinolones by linear sweep stripping voltammetry with the aid of chemometrics

A linear sweep stripping voltammetric (LSSV) method has been researched and developed for simultaneous quantitative determination of mixtures of three antibiotic drugs, ofloxacin, norfloxacin and ciprofloxacin. It relies on reductive reaction of the antibiotics at a mercury electrode in a Britton-Robinson buffer (pH 3.78). The voltammograms of these three compounds overlap strongly, and show non-linear character. Thus, it is difficult to analyse the compounds individually in their mixtures. In this work, chemometrics methods such as classical least squares (CLS), principal component regression (PCR), partial least squares (PLS) and radial basis function-artificial neural networks (RBF-ANN) were applied for the simultaneous determination of these compounds. The prediction performance of the calibration models constructed on the basis of these methods was compared. It was shown that satisfactory quantitative results were obtained with the use of the RBF-ANN calibration model relative prediction error (RPE_T) of 8.1% and an average recovery of 101%. This method is able to accommodate non-linear data quite well. The proposed analytical method based on LSSV was applied for the analysis of ofloxacin, norfloxacin and ciprofloxacin antibiotics in bird feedstuffs and their spiked samples, as well as in eye drops with satisfactory results.     

Simultaneous determination of ascorbic acid,epinephrine, and uric acid by differential pulse voltammetry using poly(p-xylenolsulfonephthalein) modified glassy carbon electrode

A novel poly(p-xylenolsulfonephthalein) modified glassy carbon electrode was prepared for the simultaneous determination of ascorbic acid (AA), epinephrine (EP) and uric acid (UA). Cyclic voltammetric, chronoamperometric, and differential pulse voltammetric methods were used to investigate the modified electrode for the electrocatalytic oxidation of EP, AA, and UA in aqueous solutions. The separation of the oxidation peak potentials for AA–EP and EP–UA was about 200 and 130 mV, respectively. The calibration curves obtained for AA, EP, and UA were in the ranges of 10–1343, 2–390, and 0.1–560 μmol L⁻¹, respectively. The detection limits (S/N = 3) were 4, 0.1, and 0.08 μmol L⁻¹ for AA, EP and UA, respectively. The diffusion coefficient and the catalytic rate constant for the oxidation of EP at the modified electrode were calculated as 1.40(±0.10) × 10⁻⁴ cm² s⁻¹ and 1.06 × 10³ mol⁻¹ L s⁻¹, respectively. The present method was applied to the determination of EP in pharmaceutical and urine samples, AA in commercially available vitamin C tablet, and EP plus UA in urine samples.     

Simultaneous determination of dopamine and ascorbic acid on poly (3,4-ethylenedioxythiophene) modified glassy carbon electrode

Detection of dopamine (DA) in the presence of excess of ascorbic acid (AA) has been demonstrated using a conducting polymer matrix, poly (3,4-ethylenedioxythiophene) (PEDOT) film in neutral buffer (PBS 7.4) solution. The PEDOT film was deposited on a glassy carbon electrode by electropolymerization of EDOT from acetonitrile solution. Atomic force microscopy studies revealed that the electrodeposited film was found to be approximately 100 nm thick with a roughness factor of 2.6 nm. Voltammetric studies have shown catalytic oxidation of DA and AA on PEDOT modified electrode and can afford a peak potential separation of ∼0.2 V. It is speculated that the cationic PEDOT film interacts with the negatively charged ascorbate anion through favorable electrostatic interaction, which results in pre-concentration at a less anodic value. The positively charged DA tends to interact with the hydrophobic regions of PEDOT film through hydrophobic–hydrophobic interaction thus resulting in favorable adsorption on the polymer matrix. Further enhancement in sensitivity to micro molar level oxidation current for DA/AA oxidation was achieved by square wave voltammetry (SWV) which can detect DA at its low concentration of 1 μM in the presence of 1000 times higher concentration of AA (1 mM). Thus the PEDOT modified electrode exhibited a stable and sensitive response to DA in the presence of AA interference.     

Simultaneous electrochemical determination of norepinephrine,ascorbic acid and uric acid using a graphene modified glassy carbon electrode

This paper describes the simultaneous determination of ascorbic acid (AA), norepinephrine (NE) and uric acid (UA) using a graphene modified glassy carbon electrode (GME) in pH 4.0 phosphate buffer solution. The electrochemical behaviors of AA, NE and UA at a bare glassy carbon electrode (GCE) and the GME were studied by cyclic voltammetry. Bare GCE failed to resolve the voltammetric signals of AA, NE and UA in a mixture, whereas the GME not only resolved their voltammetric signals, but also exhibited excellent electrocatalytic activity towards their electrochemical oxidation. The oxidation peak currents of AA, NE and UA were linearly proportional to their concentrations over the range of 1.0.0–1000.0, 0.6–45.0 and 1.0–100.0 μM, respectively, and their detection limits were 1.2, 0.10 and 0.60 μM, respectively, The modified electrode is of excellent sensitivity and selectivity, and has been satisfactorily used for the simultaneous determination of AA, NE and UA in their ternary mixture.     

普鲁士蓝纳米碳管修饰玻碳电极测定吡虫啉的研究

用纳米碳管修饰的玻碳电极以0.1 mol/L NH3-NH4Cl缓冲溶液为底液,用线性扫描伏安法对吡虫啉农药进行了测定。吡虫啉在-1.04 V出现的还原峰电流的大小与吡虫啉的浓度在1.34×10-7~2.94×10-5mol/L范围内呈良好的线性关系。本方法的检出限为5.0×10-8mol/L。本文对不同的修饰电极性能进行了研究,结果发现在玻碳电极上先修饰普鲁士蓝再修饰纳米碳管的电极对吡虫啉的响应最好,峰型最好,峰电流最大,测定最灵敏。     

Docosyltrimethylammonium chloride modified glassy carbon electrode for simultaneous determination of dopamine and ascorbic acid

A glassy carbon electrode (GCE) modified with docosyltrimethylammonium chloride (DCTMACl) is used for simultaneous determination of dopamine (DA) and ascorbic acid (AA) using differential pulse voltammetry (DPV) technique in 0.10 mol·L^?1 phosphate buffer solution of pH 5.0. The cationic surfactant DCTMACl modified film has a positive charge. DA exists as the positively charged species, whereas AA is the negatively charged one in the solution. Thus, at DCTMACl film-modified GCE, the oxidation peak potential of AA shifts toward less negative potential and the peak current of AA increases a little, while the oxidation peak potential of DA shifts toward more positive potential and peak current decreases greatly in comparison with that on bare electrode. The two anodic peaks are separated around 200 mV. Under optimal conditions, the catalytic peak currents obtained from DPV increase linearly with concentrations of DA and AA in the ranges of 1.0?×?10^?5 to 1.0?×?10^?3?mol·L^?1. This electrode has good reproducibility, high stability in its voltammetric response, and low detection limit (micromolar) for both AA and DA. The modified electrode has been applied to the determination of DA and AA in injection.     

Simultaneous determination of dopamine, ascorbic acid and uric acid at poly (Evans Blue) modified glassy carbon electrode

A sensitive and selective electrochemical method for the determination of dopamine using an Evans Blue polymer film modified on glassy carbon electrode was developed. The Evans blue polymer film modified electrode shows excellent electrocatalytic activity toward the oxidation of dopamine in phosphate buffer solution (pH 4.5). The linear range of 1.0 x 10(-6)-3.0 x 10(-5) M and detection limit of 2.5 x 10(-7) M were observed in pH 4.5 phosphate buffer solutions. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid and uric acid. The separation of the oxidation peak potentials for dopamine-ascorbic acid and dopamine-uric acid were about 182 mV and 180 mV, respectively. The differences are large enough to determine AA, DA and UA individually and simultaneously. This work provides a simple and easy approach to selectively detect dopamine in the presence of ascorbic acid and uric acid in physiological samples.     

多巴胺和抗坏血酸在十六烷基三甲基溴化铵/碳纳米管电极上的检测

研究了十六烷基三甲基溴化铵(CTMAB)/多壁碳纳米管修饰玻碳电极的制备以及多巴胺和抗坏血酸在该修饰电极上的电化学行为。在CTMAB和多壁碳纳米管的协同作用下,该修饰电极对多巴胺和抗坏血酸均具有显著的催化氧化作用,多巴胺和抗坏血酸的氧化峰电位分别为223mV和15mV,实现了在抗坏血酸共存时测定多巴胺。在pH7.0的磷酸盐缓冲溶液中,多巴胺和抗坏血酸的线性范围分别为2.0×10-6～2.0×10-3mol/L和4.0×10-5～1.0×10-2mol/L,检出限分别为6.0×10-7mol/L和1.0×10-5mol/L。     

Simultaneous determination of dopamine and serotonin using a carbon nanotubes-ionic liquid gel modified glassy carbon electrode

An electrochemical sensor based on carbon nanotubes (CNTs)-ionic liquid (IL) composite has been developed for the simultaneous determination of serotonin (5-HT) and dopamine (DA). The CNTs-IL composite modified electrode presents excellent selectivity and sensitivity towards 5-HT and DA and eliminates the interference of ascorbic acid. The parameters which influence the determination of 5-HT and DA have been investigated. Under optimized conditions, linear calibration graphs were obtained in the range from 20 nM to 7 µM, with a detection of limit of 8 nM, for 5-HT, and in the range from 0.1 to 12 µM, with a detection of limit of 60 nM, for DA. The electrode has been applied to the assay of 5-HT and DA in human blood serum with good results.     

Simultaneous determination of dopamine,ascorbic acid and uric acid with electrospun carbon nanofibers modified electrode

A novel carbon-nanofiber-modified carbon-paste electrode (CNF-CPE) was employed for the simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with good selectivity and high sensitivity. The CNFs were prepared by combination of electrospinning technique with thermal treatment method and were used without any pretreatment. In application to determination of DA, AA and UA in the ternary mixture, the pristine CNF-CPE exhibited well-separated differential pulse voltammetric peaks with high catalytic current. Low detection limits of 0.04 μM, 2 μM and 0.2 μM for DA, AA and UA were obtained, with the linear calibration curves over the concentration range 0.04–5.6 μM, 2–64 μM and 0.8–16.8 μM, respectively.     

Simultaneous determination of acetaminophen,dopamine and ascorbic acid using a PbS nanoparticles Schiff base-modified carbon paste electrode

A highly sensitive method was investigated for the simultaneous determination of acetaminophen (AC), dopamine (DA), and ascorbic acid (AA) using a PbS nanoparticles Schiff base-modified carbon paste electrode (PSNSB/CPE). Differential pulse voltammetry peak currents of AC, DA and AA increased linearly with their concentrations within the ranges of 3.30 × 10⁻⁸–1.58 × 10⁻⁴ M, 5.0 × 10⁻⁸–1.2 × 10⁻⁴ M and 2.50 × 10⁻⁶–1.05 × 10⁻³ M, respectively, and the detection limits for AC, DA and AA were 5.36 × 10⁻⁹, 2.45 × 10⁻⁹ and 1.86 × 10⁻⁸ M, respectively. The peak potentials recorded in a phosphate buffer solution (PBS) of pH 4.6 were 0.672, 0.390, and 0.168 V (vs Ag/AgCl) for AC, DA and AA, respectively. The modified electrode was used for the determination of AC, DA, and AA simultaneously in real and synthetic samples.     

Simultaneous voltammetric measurement of ascorbic acid and dopamine on poly(caffeic acid)-modified glassy carbon electrode

A poly(caffeic acid) thin film was deposited on the surface of a glassy carbon electrode by potentiostatic technique in an aqueous solution containing caffeic acid. The poly(caffeic acid)-modified electrode was used for the determination of ascorbic acid (AA), dopamine (DA), and their mixture by cyclic voltammetry. This modified electrode exhibited a potent and persistent electron-mediating behavior followed by well-separated oxidation peaks toward AA and DA at a scan rate of 10 mV s⁻¹ with a potential difference of 135 mV, which was large enough to determine AA and DA individually and simultaneously. The catalytic peak current obtained was linearly dependent on the AA and DA concentrations in the range of 2.0 × 10⁻⁵−1.2 × 10⁻³ and 1.0 × 10⁻⁶−4.0 × 10⁻⁵ mol L⁻¹ in 0.15 mol L⁻¹ phosphate buffer (pH 6.64). The detection limits for AA and DA were 9.0 × 10⁻⁶ and 4.0 × 10⁻⁷ mol L⁻¹, respectively. The modified electrode shows good sensitivity, selectivity, and stability and has been applied to the determination of DA and AA in real samples with satisfactory results.     

Simultaneous determination of ascorbic acid,dopamine, uric acid and tryptophan on gold nanoparticles/overoxidized-polyimidazole composite modified glassy carbon electrode

A novel electrode was developed through electrodepositing gold nanoparticles (GNPs) on overoxidized-polyimidazole (PImox) film modified glassy carbon electrode (GCE). The combination of GNPs and the PImox film endowed the GNPs/PImox/GCE with good biological compatibility, high selectivity and sensitivity and excellent electrochemical catalytic activities towards ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp). In the fourfold co-existence system, the peak separations between AA–DA, DA–UA and UA–Trp were large up to 186, 165 and 285 mV, respectively. The calibration curves for AA, DA and UA were obtained in the range of 210.0–1010.0 μM, 5.0–268.0 μM and 6.0–486.0 μM with detection limits (S/N = 3) of 2.0 μM, 0.08 μM and 0.5 μM, respectively. Two linear calibrations for Trp were obtained over ranges of 3.0–34.0 μM and 84.0–464.0 μM with detection limit (S/N = 3) of 0.7 μM. In addition, the modified electrode was applied to detect AA, DA, UA and Trp in samples using standard addition method with satisfactory results.     

Stopped-flow linear sweep voltammetry at the reticulated vitreous carbon electrode in a flow injection system : Determination of dopamine in the presence of ascorbic acid

A flow injection system was used to introduce a sample in to a flow-through electrochemical cell based on a reticulated vitreous carbon (r.v.c.) electrode. Products of the initial electrolysis are trapped in the porous electrode by stopping the flow. Linear sweep voltammetry under stopped-flow conditions forms the basis of a determination of a reversibly electrolyzed species in the presence of an irreversibly electrolyzed species. The determination of dopamine in the presence of ascorbic acid was used as an illustrative example. Response varied linearly with dopamine concentration between 8 X 10^?7 and 3 X 10^?5 M and the detection limit (S/N = 3) was 5 X 10^?7 M dopamine.     

Selective determination of dopamine in the presence of high concentration of ascorbic acid using nano-Au self-assembly glassy carbon electrode

The cysteamine (CA) was bound onto surface of the pretreated glassy carbon electrode (GC) with cyclic voltammetry (CV). Gold nanoparticles were self-assembled to the electrode binding with cysteamine via strong AuS covalent bond to fabricate the nano-Au self-assembled modified electrode (nano-Au/CA/GC). The modified electrode was characterized with cyclic voltammetric and ac impedance methods. The electrochemical behavior of dopamine (DA) on the modified electrode was investigated with cyclic voltammetry and differential pulse voltammetry (DPV). A well-defined redox peaks of DA on the nano-Au/CA/GC electrode were obtained at E_pa = 0.175 V and E_pc = 0.146 V (vs. SCE), respectively. The peak current of DA is linear with the concentration of DA in the range of 1.0 × 10⁻⁸ mol L⁻¹ to 2.5 × 10⁻⁵ mol L⁻¹, with the correlation coefficient of 0.998. The detection limit is 4.0 × 10⁻⁹ mol L⁻¹ (S/N = 3). The modified electrode exhibited an excellent reproducibility, sensibility and stability for determination of DA in the presence of high concentration AA, and can be applied to determinate dopamine injection, with satisfied result.     

多壁碳纳米管修饰碳黑微电极同时测定多巴胺和抗坏血酸

制备了多壁碳纳米管修饰碳黑微电极,研究了多巴胺(DA)和抗坏血酸(AA)在该修饰电极上的电化学行为.实验表明,在pH 7.0的PBS缓冲溶液中,该修饰电极对DA和从均具有显著的催化氧化作用,AA与DA的氧化电位分别为30 mV和280 mV(vs.SCE).利用二次导数线性扫描伏安法测定,DA与AA的线性范围分别为6.0×10-9～2.0×10-4 mol/L和2.0×10-7～1.0×10-3mol/L,检出限为2.0×10-9mol/L 和1.0×10-7mol/L.方法已用于人工合成样品的分析.