L-tryptophan is an essential amino acid for human health. Nanofibrillated cellulose (NFC) from marram grass (Ammophila arenaria) extracted from plants harvested in the center of Tunisia was used for the first time for...L-tryptophan is an essential amino acid for human health. Nanofibrillated cellulose (NFC) from marram grass (Ammophila arenaria) extracted from plants harvested in the center of Tunisia was used for the first time for the modification of a glassy carbon electrode (GCE), for the sensitive detection of L-tryptophan (Trp). After spectroscopic and morphological characterization of the extracted NFC, the GC electrode modification was monitored through cyclic voltammetry. The NFC-modified electrode exhibited good analytical performance in detecting Trp with a wide linear range between 7.5 × 10−4 mM and 10−2 mM, a detection limit of 0.2 µM, and a high sensitivity of 140.0 µA∙mM−1. Additionally, the NFC/GCE showed a good reproducibility, good selectivity versus other amino acids, uric acid, ascorbic acid, and good applicability to the detection of Trp in urine samples.展开更多
A voltammetric sensor based on the electropolymerization of cobalt-poly(methionine)(Co-poly(Met)) on a glassy carbon electrode (GCE) was developed and applied for the determination of estriol by differential pulse vol...A voltammetric sensor based on the electropolymerization of cobalt-poly(methionine)(Co-poly(Met)) on a glassy carbon electrode (GCE) was developed and applied for the determination of estriol by differential pulse voltammetry (DPV) for the first time. The electrochemical properties of the Co-poly(Met)/GCE were analysed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the polymers on the GCE surface. The deposition of the Co-poly(Met) film on the GCE surface enhanced the sensor electronic transfer. CV studies revealed that estriol exhibits an irreversible oxidation peak at t0.58 V for the Co-poly(Met)/GCE (vs. Ag/AgCl reference electrode) in 0.10 mol/L Britton-Robinson buffer solution (pH=7.0). Different voltammetric scan rates (10-200 mV/s) suggested that the estriol oxidation on the Co-poly(Met)/GCE surface is controlled by adsorption and diffusion processes. Based on the optimized DPV conditions, the linear responses for estriol quantification were from 0.596 μmol/L to 4.76 μmol/L (R2 =0.996) and from 5.66 μmol/L to 9.90 μmol/L (R2 =0.994) with a limit of detection (LOD) of 0.0340 μmol/L and a limit of quantification (LOQ) of 0.113 μmol/L. The DPV-Co-poly(Met)/GCE method provided good intra-day and inter-day repeatability with RSD values lower than 5%. Also, no interference of real sample matrices was observed on the estriol voltammetric response, making the DPV-Copoly( Met)/GCE highly selective for estriol. The accuracy test showed that the estriol recovery was in the ranges 96.7%-103% and 98.7%-102% for pharmaceutical tablets and human urine, respectively. The estriol quantification in pharmaceutical tablets performed by the Co-poly(Met)/GCE-assisted DPV method was comparable to the official analytical protocols.展开更多
A sensitive electroanalytical method for quantification of pheniramine in pharmaceutical formulation has been investigated on the basis of the enhanced electrochemical response at glassy carbon electrode modified with...A sensitive electroanalytical method for quantification of pheniramine in pharmaceutical formulation has been investigated on the basis of the enhanced electrochemical response at glassy carbon electrode modified with multi-walled carbon nanotubes in the presence of sodium lauryl sulfate.The experimental results suggest that the phcniramine in anionic surfactant solution exhibits electrocatalytic effect resulting in a marked enhancement of the peak current response.Peak current response is linearly dependent on the concentration of pheniramine in the range 200-1500 μg/mL with correlation coefficient 0.9987.The limit of detection is 58.31 μg/m L.The modified electrode shows good sensitivity and repeatability.展开更多
The glassy carbon (GC) electrode modified with a monolayer nickel hydroxide (GC/Ni(OH) 2) was prepared by immersion of GC substrate in 1.0×10 -3 mol/L NiSO 4 solution, and then cyclic voltammetric scannin...The glassy carbon (GC) electrode modified with a monolayer nickel hydroxide (GC/Ni(OH) 2) was prepared by immersion of GC substrate in 1.0×10 -3 mol/L NiSO 4 solution, and then cyclic voltammetric scanning in 0.20 mol/L KOH. Similarly, GC/Co(OH) 2 electrode was prepared too. The experiments showed that the voltammetric behavior of GC/Ni(OH) 2 electrode in 0.20 mol/L KOH is more stable than that of GC/ Co(OH) 2. It was found that the GC/Ni(OH) 2 electrode acts as an effective electrocatalysis for the oxidation of hydrazine.展开更多
The electrochemical behavior of epinephrine at activated glassy carbon electrode and carbon nanotube-coated glassy carbon electrode was studied. Epinephrine could exhibit an anodic peak at about 0.2 V （vs. SCE） at b...The electrochemical behavior of epinephrine at activated glassy carbon electrode and carbon nanotube-coated glassy carbon electrode was studied. Epinephrine could exhibit an anodic peak at about 0.2 V （vs. SCE） at bare glassy carbon electrode, but it was very small. However, when the electrode was activated at certain potential （i.e. 1.9 V） or modified with carbon nanotube, the peak became more sensitive, resulting from the increase in electrode area in addition to the electrostatic attraction. Under the selected conditions, the anodic peak current was linear to epinephrine concentration in the range of 3.3×10^-7 - 1.1×10^-5 mol/L at activated glassy carbon electrode and in the range of 1.0×10^-5 - 5.0×10^-5 mol/L at carbon nanotube-coated electrode. The correlation coefficients were 0.998 and 0.997, respectively. The determination limit was 1.0×10^-7 mol/L. The two electrodes have been successfully applied for the determination of epinephrine in adrenaline hydrochloride injection with recovery of 95%-104%.展开更多
The multi-wall carbon nanotubes（MWNTs）modified glassy carbon electrode（CNT/GCE）was fabricated and its electrocatalytic activity of hydroquinone was investigated.It was found that the electrochemical behaviors were...The multi-wall carbon nanotubes（MWNTs）modified glassy carbon electrode（CNT/GCE）was fabricated and its electrocatalytic activity of hydroquinone was investigated.It was found that the electrochemical behaviors were greatly improved at CNT/GC,indicating that the redox of hydroquinone could be catalyzed at CNT/GC.The kinetic parameters of thisprocess were calculated.The diffusiong coefficient was 1.7×10-5cm2·s-1,the heterogeneouselectron transfer rate constant k was 0.678s-1,α value was 0.538 and electron transfer numbers was 2.展开更多
Electrochemical oxidation reactions of L ascorbic acid(AA) at a copper cobalt hexacyanoferrate modified electrode(CoCuHCF/Pt) in neutral solutions were studied in comparison with that at a bared Pt electrode by in sit...Electrochemical oxidation reactions of L ascorbic acid(AA) at a copper cobalt hexacyanoferrate modified electrode(CoCuHCF/Pt) in neutral solutions were studied in comparison with that at a bared Pt electrode by in situ FTIR reflection absorption spectroscopy(FTIRRAS). The results indicated that the electrode oxidation of AA at both the electrodes CoCuHCF followed by chemical processes. AA is oxidized to dehydro L ascorbic acid(DHA) followed by a chemical hydration process. At Pt electrode, the DHA underwent hydration reaction to form bicyclic product, which then further was transformed into 2,3 diketogulonic acid and its enol form via an opening of lactone ring. However, at CoCuHCF/Pt electrode, the DHA undergoes ring opening reaction and then degradation reaction.展开更多
文摘L-tryptophan is an essential amino acid for human health. Nanofibrillated cellulose (NFC) from marram grass (Ammophila arenaria) extracted from plants harvested in the center of Tunisia was used for the first time for the modification of a glassy carbon electrode (GCE), for the sensitive detection of L-tryptophan (Trp). After spectroscopic and morphological characterization of the extracted NFC, the GC electrode modification was monitored through cyclic voltammetry. The NFC-modified electrode exhibited good analytical performance in detecting Trp with a wide linear range between 7.5 × 10−4 mM and 10−2 mM, a detection limit of 0.2 µM, and a high sensitivity of 140.0 µA∙mM−1. Additionally, the NFC/GCE showed a good reproducibility, good selectivity versus other amino acids, uric acid, ascorbic acid, and good applicability to the detection of Trp in urine samples.
基金CNPq (454438/2014-1)CAPES+1 种基金FINEPFAPEMIG for the financial support to this work
文摘A voltammetric sensor based on the electropolymerization of cobalt-poly(methionine)(Co-poly(Met)) on a glassy carbon electrode (GCE) was developed and applied for the determination of estriol by differential pulse voltammetry (DPV) for the first time. The electrochemical properties of the Co-poly(Met)/GCE were analysed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the polymers on the GCE surface. The deposition of the Co-poly(Met) film on the GCE surface enhanced the sensor electronic transfer. CV studies revealed that estriol exhibits an irreversible oxidation peak at t0.58 V for the Co-poly(Met)/GCE (vs. Ag/AgCl reference electrode) in 0.10 mol/L Britton-Robinson buffer solution (pH=7.0). Different voltammetric scan rates (10-200 mV/s) suggested that the estriol oxidation on the Co-poly(Met)/GCE surface is controlled by adsorption and diffusion processes. Based on the optimized DPV conditions, the linear responses for estriol quantification were from 0.596 μmol/L to 4.76 μmol/L (R2 =0.996) and from 5.66 μmol/L to 9.90 μmol/L (R2 =0.994) with a limit of detection (LOD) of 0.0340 μmol/L and a limit of quantification (LOQ) of 0.113 μmol/L. The DPV-Co-poly(Met)/GCE method provided good intra-day and inter-day repeatability with RSD values lower than 5%. Also, no interference of real sample matrices was observed on the estriol voltammetric response, making the DPV-Copoly( Met)/GCE highly selective for estriol. The accuracy test showed that the estriol recovery was in the ranges 96.7%-103% and 98.7%-102% for pharmaceutical tablets and human urine, respectively. The estriol quantification in pharmaceutical tablets performed by the Co-poly(Met)/GCE-assisted DPV method was comparable to the official analytical protocols.
文摘A sensitive electroanalytical method for quantification of pheniramine in pharmaceutical formulation has been investigated on the basis of the enhanced electrochemical response at glassy carbon electrode modified with multi-walled carbon nanotubes in the presence of sodium lauryl sulfate.The experimental results suggest that the phcniramine in anionic surfactant solution exhibits electrocatalytic effect resulting in a marked enhancement of the peak current response.Peak current response is linearly dependent on the concentration of pheniramine in the range 200-1500 μg/mL with correlation coefficient 0.9987.The limit of detection is 58.31 μg/m L.The modified electrode shows good sensitivity and repeatability.
文摘The glassy carbon (GC) electrode modified with a monolayer nickel hydroxide (GC/Ni(OH) 2) was prepared by immersion of GC substrate in 1.0×10 -3 mol/L NiSO 4 solution, and then cyclic voltammetric scanning in 0.20 mol/L KOH. Similarly, GC/Co(OH) 2 electrode was prepared too. The experiments showed that the voltammetric behavior of GC/Ni(OH) 2 electrode in 0.20 mol/L KOH is more stable than that of GC/ Co(OH) 2. It was found that the GC/Ni(OH) 2 electrode acts as an effective electrocatalysis for the oxidation of hydrazine.
文摘The electrochemical behavior of epinephrine at activated glassy carbon electrode and carbon nanotube-coated glassy carbon electrode was studied. Epinephrine could exhibit an anodic peak at about 0.2 V （vs. SCE） at bare glassy carbon electrode, but it was very small. However, when the electrode was activated at certain potential （i.e. 1.9 V） or modified with carbon nanotube, the peak became more sensitive, resulting from the increase in electrode area in addition to the electrostatic attraction. Under the selected conditions, the anodic peak current was linear to epinephrine concentration in the range of 3.3×10^-7 - 1.1×10^-5 mol/L at activated glassy carbon electrode and in the range of 1.0×10^-5 - 5.0×10^-5 mol/L at carbon nanotube-coated electrode. The correlation coefficients were 0.998 and 0.997, respectively. The determination limit was 1.0×10^-7 mol/L. The two electrodes have been successfully applied for the determination of epinephrine in adrenaline hydrochloride injection with recovery of 95%-104%.
文摘The multi-wall carbon nanotubes（MWNTs）modified glassy carbon electrode（CNT/GCE）was fabricated and its electrocatalytic activity of hydroquinone was investigated.It was found that the electrochemical behaviors were greatly improved at CNT/GC,indicating that the redox of hydroquinone could be catalyzed at CNT/GC.The kinetic parameters of thisprocess were calculated.The diffusiong coefficient was 1.7×10-5cm2·s-1,the heterogeneouselectron transfer rate constant k was 0.678s-1,α value was 0.538 and electron transfer numbers was 2.
文摘Electrochemical oxidation reactions of L ascorbic acid(AA) at a copper cobalt hexacyanoferrate modified electrode(CoCuHCF/Pt) in neutral solutions were studied in comparison with that at a bared Pt electrode by in situ FTIR reflection absorption spectroscopy(FTIRRAS). The results indicated that the electrode oxidation of AA at both the electrodes CoCuHCF followed by chemical processes. AA is oxidized to dehydro L ascorbic acid(DHA) followed by a chemical hydration process. At Pt electrode, the DHA underwent hydration reaction to form bicyclic product, which then further was transformed into 2,3 diketogulonic acid and its enol form via an opening of lactone ring. However, at CoCuHCF/Pt electrode, the DHA undergoes ring opening reaction and then degradation reaction.
