Rapid Assay of Bisphenol A Released from Baby Feeding Bottles by Adsorptive Stripping Voltammetry on a Diphenylether Carbon Paste Electrode

This work reports the determination of bisphenol A (BPA) released from baby feeding bottles by adsorptive stripping voltammetry on a diphenylether carbon paste electrode (DPE-CPE). BPA was as accumulated on the surface of the DPE-CPE by an adsorptive/extractive mechanism at ?0.20 V in B-R buffer at pH 7.0. Following pre-concentration, an anodic scan was applied in the range ?0.20 V to +1.00 V during which BPA was oxidized and the oxidation peak current was related to the BPA concentration in the sample. The parameters related to both the preconcentration and stripping step were investigated. Using the selected conditions, the limit of detection for BPA was 7.8 × 10^?9 mol L^?1 at a preconcentration time of 240 s and the % relative standard deviation was 4.2% for 6.7 × 10^?7 mol L^?1 of BPA (n = 8). The proposed method was applied to the determination of BPA leaching from polycarbonate baby feeding bottles under simulated conditions of typical use. The results compared well with those obtained with liquid chromatography-tandem mass spectrometry (LC-MS/MS).     

Electrocatalytic study of an electrode modified with Reactive Blue 4 dye covalently immobilized on amine-functionalized silica

In the present work, we investigated the immobilization and electrochemical behavior of Reactive Blue 4 dye on 3-aminopropyl-functionalized silica. The electrochemical behavior of the modified electrode and the electro-oxidation of dipyrone were studied by cyclic voltammetry. The modified electrode showed a well-defined redox coupling with a formal potential of 0.45 V (vs. saturated calomel reference electrode) assigned to anthraquinone/anthrahydroquinone redox process (pH?=?2). The modified electrode also demonstrated electrocatalytic activity and an increased peak current towards the oxidation of dipyrone at a reduced overall potential. The electrocatalytic process was found to be highly dependent on the pH of the supporting electrolyte. The voltammetric responses for dipyrone were linear in the concentration range of 49.9 to 440 μmol L^?1 at a pH of 2.0 with a detection limit and sensitivity of 22.0 μmol L^?1 and 0.0278 μA mmol L^?1, respectively.     

Voltammetric Determination of Dopamine in Human Serum and Urine at a Glassy Carbon Electrode Modified by Cysteic Acid Based on Electrochemical Oxidation of L ‐cysteine

Abstract

The voltammetric behavior of dopamine was studied at a glassy carbon electrode modified by cysteic acid, based on electrochemical oxidation of L ‐cysteine. The modified electrode showed strong electrocatalytic activity towards dopamine and good selectivity. In a phosphate buffer solution (pH 7.4), the anodic peak current obtain from the differential pulse voltammetry of dopamine was linearly dependent on its concentration in the range of 5×10^?9 to 4.0×10^?6mol · L^?1, with a detection limit of 2×10^?9mol · L^?1. The low‐cost modified electrode had been applied to the determination of dopamine in human serum and urine samples with satisfactory results.     

Amperometric Nitric Oxide Sensor Based on Poly(Thionine)/Nafion‐Modified Electrode and Its Application in Monitoring Nitric Oxide Release from Rat Kidney

Abstract

A novel amperometric nitric oxide (NO) sensor based on a glassy carbon electrode modified with thionine and Nafion films has been developed. The oxidation peak current of NO increased significantly at the poly(thionine)/Nafion‐modified glassy carbon electrode (GCE), which can be used for the detection of NO. The oxidation peak current was linear with the concentration of nitric oxide over the range from 3.6×10^?7 to 6.8×10^?5 mol · L^?1, and the detection limit was 7.2×10^?8 mol · L^?1. This nitric oxide sensor showed high selectivity to nitric oxide determination, and some potential interference could be eliminated effectively. The nitric oxide sensor has been applied to monitor NO release from rat kidney stimulated by L‐arginine. The results indicated the applicability of the NO sensor to biomedical samples.     

Direct Electroanalytical Determination of Fluvastatin in a Pharmaceutical Dosage Form: Batch and Flow Analysis

Abstract

The reduction of luvastatin (FLV) at a hanging mercury-drop electrode (HMDE) was studied by square-wave adsorptive-stripping voltammetry (SWAdSV). FLV can be accumulated and reduced at the electrode, with a maximum peak current intensity at a potential of approximately ?1.26 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 5.25. The method shows linearity between peak current intensity and FLV concentration between 1.0 × 10^?8 and 2.7 × 10^?6 mol L^?1. Limits of detection (LOD) and quantification (LOQ) were found to be 9.9 × 10^?9 mol L^?1 and 3.3 × 10^?8 mol L^?1, respectively.

Furthermore, FLV oxidation at a glassy carbon electrode surface was used for its hydrodynamic monitoring by amperometric detection in a flow-injection system. The amperometric signal was linear with FLV concentration over the range 1.0 × 10^?6 to 1.0 × 10^?5 mol L^?1, with an LOD of 2.4 × 10^?7 mol L^?1 and an LOQ of 8.0 × 10^?7 mol L^?1. A sample rate of 50 injections per hour was achieved.

Both methods were validated and showed to be precise and accurate, being satisfactorily applied to the determination of FLV in a commercial pharmaceutical.     

Evaluation of the Potentialities of a Carbon Nanotubes/Silicone Rubber Composite Electrode in the Determination of Hydrochlorothiazide

A multiwall carbon nanotube/silicone rubber (MWCNT/SR) composite electrode has been used for the determination of hydrochlorothiazide (HCTZ) in pharmaceutical formulations by differential pulse voltammetry (DPV). The electro-oxidation process was evaluated by cyclic voltammetry, from which it was observed that HCTZ presents an irreversible oxidation peak at 0.82 V vs. saturated calomel electrode (SCE) in the potential range from 0.5 to 1.1 V, in Britton-Robinson buffer pH 7.0 at MWCNT/SR. HCTZ was determined by DPV using a MWCNT/SR 70% (MWCNT, m/m) composite electrode after the optimization of the experimental parameters. The linear range was from 5.0 to 70.0 µ mol L^?1, with a limit of detection (LOD) of 2.6 µ mol L^?1. The HCTZ was determined in pharmaceutical formulations using the proposed composite electrode and the results agreed with those from the official high performance liquid chromatography (HPLC) method within 95% confidence level, according to the t-Student test.     

Poly(2-amino-5-(4-pyridinyl)-1, 3, 4-thiadiazole) film modified electrode for the simultaneous determinations of dopamine, uric acid and nitrite

Poly(2-amino-5-(4-pyridinyl)-1,3,4-thiadiazole) (PAPT) modified glassy carbon electrode (GCE) was fabricated and used for the simultaneous determinations of dopamine (DA), uric acid (UA) and nitrite (NO₂ ^?) in 0.1 mol?L^?1 phosphate buffer solution (PBS, pH 5.0) by using cyclic voltammetry and differential pulse voltammetry (DPV) techniques. The results showed that the PAPT modified GCE (PAPT/GCE) not only exhibited electrocatalytic activities towards the oxidation of DA, UA and NO₂ ^? but also could resolve the overlapped voltammetric signals of DA, UA and NO₂ ^? at bare GCE into three strong and well-defined oxidation peaks with enhanced current responses. The peak potential separations are 130 mV for DA–UA and 380 mV for UA–NO₂ ^? using DPV, which are large enough for the simultaneous determinations of DA, UA and NO₂ ^?. Under the optimal conditions, the anodic peak currents were correspondent linearly to the concentrations of DA, UA and NO₂ ^? in the ranges of 0.95–380 μmol?L^?1, 2.0–1,000 μmol?L^?1 and 2.0–1,200 μmol?L^?1 for DA, UA and NO₂ ^?, respectively. The correlation coefficients were 0.9989, 0.9970 and 0.9968, and the detection limits were 0.2, 0.35 and 0.6 μmol?L^?1 for DA, UA and NO₂ ^?, respectively. In 0.1 mol?L^?1 PBS pH 5.0, the PAPT film exhibited good electrochemical activity, showing a surface-controlled electrode process with the apparent heterogeneous electron transfer rate constant (k _s) of 25.9 s^?1 and the charge–transfer coefficient (α) of 0.49, and thus displayed the features of an electrocatalyst. Due to its high sensitivity, good selectivity and stability, the modified electrode had been successfully applied to the determination of analytes in serum and urine samples.     

The electrochemistry of uric acid at a gold electrode modified with L-cysteine, and its application to sensing uric urine

The electrochemistry of uric acid at a gold electrode modified with a self-assembled film of L-cysteine was studied by cyclic voltammetry and differential pulse voltammetry. Compared to the bare gold electrode, uric acid showed better electrochemical response in that the anodic peak current is stronger and the peak potential is negatively shifted by about 100 mV. The effects of experimental conditions on the oxidation of uric acid were tested and a calibration plot was established. The differential pulse response to uric acid is linear in the concentration range from 1.0?×?10^?6 to ~?1.0?×?10^?4 mol?L^?1 (r?=?0.9995) and from 1.0?×?10^?4 to ~?5.0?×?10^?4 mol?L^?1 (r?=?0.9990), the detection limit being 1.0?×?10^?7 mol?L^?1 (at S/N?=?3). The high sensitivity and good selectivity of the electrode was demonstrated by its practical application to the determination of uric acid in urine samples.

Simultaneous voltammetric determination of uric acid and ascorbic acid using carbon paste/cobalt Schiff base composite electrode

Differential pulse and cyclic voltammetry were applied for the oxidation of mixture of uric acid and ascorbic acid at the surface of carbon paste/cobalt Schiff base composite electrode. The electrooxidation of these compounds at bare electrode is sluggish, and there is no suitable peak separation between them. However, using cobalt methyl salophen as modifier, two well-defined anodic waves with a considerable enhancement in the peak current and a remarkable peak potential separation near 315 mV are obtained. It can improve the kinetics of electron transfer for both compounds remarkably. All these improvements are created because of the electrocatalytic property of cobalt Schiff base complex. The effect of some parameters such as pH and scan rates were studied. All the anodic peak currents for the oxidation of ascorbic acid and uric acid shifted toward more negative potential with an increase in pH, revealing that protons have taken part in their electrode reaction processes. The best peak separation with appropriate current was obtained for pH 4.0. A linear range of 5.0?×?10^?4 to 1.0?×?10^?8 and 1.0?×?10^?3 to 1.0?×?10^?8 M with detection limit of 8.0?×?10^?9 and 8.0?×?10^?9 M was obtained for ascorbic acid and uric acid using differential pulse voltammetry at the surface of modified electrode, respectively. Analytical utility of the modified electrode has been examined successfully using human urine samples and vitamin C commercial tablets.     

Sensitive electrochemical detection of bisphenol A with chitosan and urchinlike MnO2 microsphere modified carbon ionic liquid electrode

In this article, a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid N-hexylpyridinium hexafluorophosphate as the binder and the modifier. Then urchinlike MnO₂ microsphere and chitosan (CTS) was further casted on the CILE surface step-by-step to get a modified electrode that was denoted as CTS/MnO₂/CILE. Cyclic voltammetric studies indicated that bisphenol A (BPA) exhibited a well-defined oxidation peak at 0.486 V in 22.83 g L^?1 pH 8.0 Britton?Robinson buffer solution, which was attributed to the electro-oxidation of BPA on the modified electrode. The presence of urchinlike MnO₂ microsphere on the electrode surface could increase the oxidation peak current (I_pa) greatly, which may be due to the larger surface area that could adsorb more BPA on the electrode surface. Electrochemical parameters of BPA on the modified electrode were calculated with the electron transfer coefficient (α) as 0.66 and the apparent heterogeneous electron transfer rate constant (ks) as 0.50 s^?1. Under the optimal conditions, a linear relationship between the I_pa of BPA and its concentration was obtained in the range from 1.37 × 10^–1 mg L^?1 to 182.6 mg L^?1 with the detection limit as 7.31 × 10^–3 mg L^?1 (3σ). The CTS/MnO₂/CILE was applied to the detection of BPA content in different kinds of samples with satisfactory results.     

Highly selective determination of ascorbic acid,epinephrine, and uric acid by differential pulse voltammetry using poly(Adizol Black B)-modified glassy carbon electrode

A polymerized film of Adizol Black B (ABB) on the surface of glassy carbon (GC) electrode was prepared for the simultaneous determination of ascorbic acid (AA), epinephrine (EP), and uric acid (UA). This new electrode presented an excellent electrocatalytic activity towards the oxidation of AA, EP, and UA by differential pulse voltammetry method. The oxidation peaks of the three compounds were well defined and had the enhanced peak currents. The separation of the oxidation peak potentials for AA–EP and EP–UA were about 180 and 130 mV, respectively. The calibration curves obtained for AA, EP, and UA were in the ranges of 2.0–1,970.0, 0.1–64.0, and 0.1–1,700.0 μmol L^–1, respectively. The detection limits (S/N?=?3) were 0.01, 0.007, and 0.02 μmol L^–1 for AA, EP, and UA, respectively. The diffusion coefficient and the catalytic rate constant for the oxidation reaction of EP at poly(ABB) film-coated GC electrode were calculated as 1.54(±0.10)?×?10^?4 cm² s^?1 and 4.5?×?10³ mol^?1 L s^?1, respectively. The present method was applied to the determination of EP in pharmaceutical, AA in commercially available vitamin C tablet, and UA in urine samples.     

Determination of Some Phenothiazines Compounds in Pharmaceuticals and Human Body Fluid by Electrocatalytic Oxidation at a Glassy Carbon Electrode Using Methylene Blue as a Mediator

Abstract

A glassy carbon electrode plus Methylene blue as a mediator was employed to study and sense the electrocatalytic oxidation of phenothiazines, including chlorpromazine, perphenazine, promazine, and fluphenazine, using cyclic voltammetry and chronoamperometry as diagnostic techniques. The electron-transfer coefficient, alpha (= 0.45), for phenothiazines compounds at the surface of glassy carbon electrode was determined using a cyclic voltammetry technique. It was found that under a selected pH (8.6) the peak current due to the oxidation of Methylene blue at the surface of the electrode that occurrs at a potential of about ? 180 mV is proportional to the phenothiazines concentration. Linear analytical curves were obtained in the ranges of 1.0 × 10^?6 ? 2.1 × 10^?4 mol L^?1 for the phenothiazines compounds. The influences of potentially interfering substances on the current response of the system were examined. The method was used for the determination of phenothiazines compounds, including chlorpromazine, perphenazine, promazine, and fluphenazine in human.     

Determination of α‐Lipoic acid on a Pyrolytic Graphite Electrode Modified with Cobalt Phthalocyanine

In this work voltammetric techniques were explored for quantification of α‐Lipoic acid (ALA) using a pyrolytic graphite electrode modified with cobalt phthalocyanine. Cyclic voltammograms recorded in phosphate buffer solution containing 1×10^?3 mol L^?1 of ALA presented an oxidation peak located at +0.8 V vs. SCE. The modification of the electrode produced a 100 mV shift of the onset oxidation potential to less positive value and a substantial increase in the ALA oxidation current. Among the voltammetric techniques explored, differential pulse voltammetry showed the best performance for quantifications of the analyte in low concentrations. Limits of detection and quantification of ALA obtained corresponds to 3.4×10^?9 mol L^?1 and 1.2×10^?8 mol L^?1, respectively.     

Electrochemical oxidation behavior of 8-azaguanine at graphene-Nafion composite film-modified glassy carbon electrode

A simple but highly sensitive electrochemical sensor for the determination of 8-azaguanine based on graphene-Nafion nanocomposite film-modified glassy carbon electrode (G-Nafion/GCE) was reported. The electrochemical behaviors of 8-azaguanine at G-Nafion/GCE were investigated by cyclic voltammetry (CV), square wave voltammetry (SWV), chronoamperometry (CA), and chronocoulometry (CC). The results showed that the electrochemical sensor exhibited excellent electrocatalytic activity to 8-azaguanine. 8-Azaguanine can be effectively accumulated at G-Nafion/GCE and produce a sensitive anodic peak, due to the synergetic functions of graphene and Nafion. Under the selected conditions, the modified electrode in pH 1.98 Britton-Robinson buffer solution showed a linear voltammetric response to 8-azaguanine within the concentration range of 5.0 × 10^?8～3.0 × 10^?5 mol L^?1, with the detection limit of 1.0 × 10^?8 mol L^?1. And, the method was also applied to detect 8-azaguanine in spiked human urine with wonderful satisfactory results.     

Electrocatalytic Determination of Ampicillin Using Carbon-Paste Electrode Modified with Ferrocendicarboxylic Acid

Abstract

A carbon-paste electrode spiked with ferrocenedicarboxylic acid (FDCMCPE) was constructed by incorporation of ferrocenedicarboxylic acid in a graphite powder–paraffin oil matrix. It has been shown by direct current cyclic voltammetry and double-step chronoamperometry that this electrode can catalyze the oxidation of ampicillin (AMPC) in aqueous buffered solution. It has been found that under the optimum condition (pH 10.0) in cyclic voltammetry, the oxidation of AMPC occurred at a potential of about 480 mV on the surface of the modified carbon-paste electrode. The kinetic parameters such as electron-transfer coefficient, α, and rate constant for the chemical reaction between AMPC and redox sites in FDCMCPE were also determined using electrochemical approaches. Under the optimized conditions, the electrocatalytic oxidation peak current of AMPC showed two linear dynamic ranges with a detection limit of 0.67 µmol L^?1 AMPC. The linear calibration was in the range of 2.34–30 µmol L^?1 and 40–700 µmol L^?1 AMPC using the differential pulse voltammetric method. Finally, this method was also examined as a selective, simple, and precise electrochemical sensor for the determination of AMPC in real samples such as drugs and urine.     

Structural characterization of electrochemically and in vitro biologically generated oxidation products of atorvastatin using UHPLC/MS/MS

Ultrahigh-performance liquid chromatography coupled with high-mass-accuracy tandem mass spectrometry (UHPLC–MS–MS) has been used for elucidation of the structures of oxidation products of atorvastatin (AT), one of the most popular commercially available drugs. The purpose of the study was identification of AT metabolites in rat hepatocytes and comparison with electrochemically generated oxidation products. AT was incubated with rat hepatocytes for 24 h. Electrochemical oxidation of AT was performed by use of a three-electrode off-line system with a glassy carbon working electrode. Three supporting electrolytes (0.1 mol L^?1 H₂SO₄, 0.1 mol L^?1 HCl, and 0.1 mol L^?1 NaCl) were tested, and dependence on pH was also investigated. AT undergoes oxidation by a single irreversible process at approximately +1.0 V vs. Ag/AgCl electrode. The results obtained revealed a simple and relatively fast way of determining the type of oxidation and its position, on the basis of characteristic neutral losses (NLs) and fragment ions. Unfortunately, different products were obtained by electrochemical oxidation and biotransformation of AT. High-mass-accuracy measurement combined with different UHPLC–MS–MS scans, for example reconstructed ion-current chromatograms, constant neutral loss chromatograms, or exact mass filtering, enable rapid identification of drug-related compounds. β-Oxidation, aromatic hydroxylation of the phenylaminocarbonyl group, sulfation, AT lactone and glycol formation were observed in rat biotransformation samples. In contrast, a variety of oxidation reactions on the conjugated skeleton of isopropyl substituent of AT were identified as products of electrolysis.

Modified Glassy Carbon Electrode with Multiwall Carbon Nanotubes as a Voltammetric Sensor for Determination of Leucine in Biological and Pharmaceutical Samples

Abstract

A simple and highly sensitive method is described for voltammetric determination of leucine in blood and urine samples; namely, a glassy carbon electrode with an effective method is modified with multiwall carbon nanotubes (MWNTs). The cyclic voltammetric results indicated that MWNTs remarkably enhanced electrocatalytic activity toward the oxidation of leucine. Under the optimum condition the calibration curve was linear in the concentration range 9.0 × 10^?6 ? 1.5 × 10^?3 mol L^?1, with the detection limit of 3.0 × 10^?6 mol L^?1 and a relative standard deviation (RSD%) lower than 3.0% (n = 5). Also, some kinetic parameters were determined and a multistep mechanism for oxidation of leucine was proposed.     

Amperometric determination of the insecticide fipronil using batch injection analysis: comparison between unmodified and carbon-nanotube-modified electrodes

The electrochemical oxidation of fipronil is investigated on unmodified and multi-walled carbon-nanotube (MWCNT)-modified glassy carbon electrodes (GCEs), and its amperometric determination using batch injection analysis (BIA) is demonstrated. An oxidation peak was observed at 1.5 V in a 0.1 mol L^?1 HClO₄/acetone solution (50:50, v/v) on both surfaces. Although MWCNT-modified GCE provided greater sensitivity, the unmodified GCE showed low RSD value, wider linear range, and reduced adsorption of fipronil or its oxidized products on the electrode surface. A detection limit of 4.7 μmol L^?1 and linear range of 25–300 μmol L^?1 were obtained using a bare GCE. The method was applied in veterinary formulations with results in agreement with those obtained by high-performance liquid chromatography.     

A novel biosensor based on ZnO nanoparticle/1,3-dipropylimidazolium bromide ionic liquid-modified carbon paste electrode for square-wave voltammetric determination of epinephrine

The direct electrochemistry of epinephrine (EP) on a modified carbon paste electrode (CPE) was described. The electrode was modified with Zinc oxide (ZnO) nanoparticles and 1,3-dipropylimidazolium bromide as a binder. The oxidation peak potential of EP at the surface of the ionic liquid ZnO nanoparticle CPE (IL/ZnO/NP/CPE) appeared at 350 mV, which was about 80 mV lower than the oxidation peak potential at the surface of the traditional carbon CPE under a similar condition. On other hand, the oxidation peak current was increased for about three times at the surface of IL/ZnO/NP/CPE compared to CPE. The linear response range and detection limit were found to be 0.09–800 μmol L^?1 and 0.06 μmol L^?1, respectively. Other physiological species did not interfere in the determination of EP at the surface of the proposed sensor in the optimum condition. The proposed sensor was successfully applied for the determination of EP in real samples.     

Electrochemical Reduction and Voltammetric Determination of Metronidazole Benzoate at Modified Carbon Paste Electrode

Abstract

A metalloporphyrin incorporated carbon paste sensor has been developed for the determination of metronidazole benzoate (MTZB). Zn(II) complex of 5,10,15,20-tetrakis (3-methoxy-4-hydroxy phenyl) porphyrin (TMHPP) was used as the active material. The MTZB gave a well-defined reduction peak at?0.713 V in 0.1 mol l^?1 phosphate buffer solution of pH around 7. Compared with bare carbon paste electrode (CPE), the TMHPP Zn(II) modified electrode significantly enhanced the reduction peak current of MTZB as well as lowered its reduction potential. Under optimum conditions the reduction peak current was proportional to MTZB concentration over the range 1 × 10^?3 mol l^?1 to 1 × 10^?5 mol l^?1. The detection limit was found to be 4.36 × 10^?6 mol l^?1. This sensor has been successfully applied for the determination of MTZB in pharmaceutical formulations and urine samples.