shohreh jahani

In this work, an easy method was employed to successfully develop La3+-doped ZnO nanoflowers and Guar-Gum (GG) modified screen printed electrode (La3+/ZnO/GG/SPE), and La3+/ZnO/GG/SPE was applied for the electrochemical detection of Ascorbic Acid (AA). The electrochemical methods, such as Cyclic Voltammetry (CV), chronoamperometry (CHA), and Differential Pulse Voltammetry (DPV) were used to evaluate the electrochemical performances toward ascorbic acid on the La3+/ZnO/GG/SPE. Good linear-ship was observed for ascorbic acid in the ranges of 1.0–700.0 μM, with the detection limits of 0.03 μM. Moreover, this sensor proved favorable to simultaneously determine ascorbic acid and acetaminophen. Finally, the modified electrode has fairly good performance during the employment of real sample analysis to determine the content of ascorbic acid. These results indicate that the La3+-doped ZnO nanoflowers are supposed to be a promising material in the electrochemical determination of ascorbic acid and acetaminophen in real samples.

Three-dimensional mesoporous CeO2 hollow sphere (M-CeO2-HS) modified glassy carbon electrode (M-CeO2-HS/GCE) was developed in this study as a very sensitive voltammetric sensor for detection of terazosin. This produced modifier was characterized by techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). There was a remarkable improvement in the electrochemical behavior relative to terazosin electro-oxidation on M-CeO2-HS/GCE surface, compared to bare GCE, in the optimized conditions of supporting electrolyte pH and casted modifier concentration. An oxidation peak was found for terazosin on modified electrode surface at the potential of about 0.57 V in phosphate buffer solution (pH=7.0). The linear dynamic range was 0.01 to 600.0 µM and the limit of detection was 1.9 nM with the aid of anodic peak of terazosin. Some advantages were reported for the modified electrode, including satisfactory reproducibility towards terazosin, potent stability, strong sensitivity and easy production. Practical applicability of the M-CeO2-HS/GCE was tested to detect the low level of terazosin in clinical and pharmaceutical formulations.

New Solid-Phase Microextraction (SPME) coating was made by electrodeposition of Zeolite Imidazolate Framework (ZIF-67) nanocrystals with the aid of polyaniline (PANI) on steel fiber. The SPME fiber was used to extract four Polycyclic Aromatic Hydrocarbons (PAHs) from the Head Space (HS) of tea infusions and determined by Gas Chromatography coupled with a Flame Ionization Detector (GC-FID). The coating of the SPME fiber was characterized by Fourier Transformed InfraRed (FT-IR) spectroscopy and Scanning Electron Microscopy (SEM). Vital parameters affecting extraction performance, including desorption conditions, salt concentration, extraction time, and temperature, have been evaluated and optimized. The validated method was specific for the PAHs analysis, with the Limit of Detection (LOD) as low as 20.0 to 50.0 ng/L. The linear range was relevant to 70.0-180.0 ng/L with a relative standard deviation (RSD) % of less than 12.8. The factor of enrichment was found to be 446.7-808.8. The synthesized coating was shown to be thermally and chemically stable. The recommended approach was successfully applied to quantify PAHs in some frequent tea infusions in the market. The fiber coating of ZIF-67 can be easily made and applied efficiently to detect PAHs pollution in the environment and food products.

A highly sensitive electrochemical sensor was fabricated based on ionic liquid and NiFe2O4 nanoparticles modified carbon paste electrode for determination of mangiferin. The modified electrode exhibited excellent electrocatalytic activity towards the oxidations mangiferin in phosphate buffer solution (pH 7.0). Cyclic voltammetry (CV), chronoamperometry (CHA) and differential pulse voltammetry (DPV) were used to investigate the electrochemical reaction of mangiferin at the modified electrode. It dramatically enhanced mangiferin oxidation current and shifted its potential towards less positive potential when compared to bare CPE. The peak current vs. mangiferin concentration diagram was found to be linear in range of 0.1 to 500.0 μM with the respective slope of 0.0576 μA μM-1. The detection limit obtained by DPV was 0.09 μM (S/N = 3). The proposed sensor was proved to be applicable for the determination of the mangiferin in urine samples.

In this study, we combined the advantages of good conductivity, small size, and large surface area and the catalytic property of La3+/Co3O4 nanoflowers to fabricate an electrochemical sensor sensitive to determination of vitamin B6 in real samples. La3+/Co3O4 nanoflowers were synthesized by a co-precipitation method which is a convenient, environment-friendly, inexpensive process. The synthesized nanoflowers were characterized by SEM. A simple and sensitive sensor based on graphite screen printed electrode (GSPE) modified by La3+/Co3O4 nanoflowers was developed for the electrochemical determination of vitamin B6. The electrochemical behavior of vitamin B6 was studied in 0.1 M phosphate buffer solution (PBS) using cyclic voltammetry (CV), chronoamperometry (CHA) and differential pulse voltammetry (DPV). The modified electrode (La3+/Co3O4NFs/GSPE) showed excellent electrocatalytic activity and remarkable sensitivity towards the oxidation of vitamin B6. The fabricated sensor displayed good operating characteristics including low detection limit, and a wide linear dynamic range for the detection of vitamin B6. Using La3+/Co3O4NFs/GSPE as the working electrode, a linear dynamic range between 1.0 to 600.0 μM and a limit of detection of 0.4 µM were obtained. Finally, reliability and accuracy of the proposed sensor were studied in real samples.

In this work, a sensitive Sudan I electrochemical sensor was assembled using NiFe2O4 nanoparticles modified screen printed electrode. Due to the synergetic effect of NiFe2O4 nanoparticles displayed high electrochemical activity with well-defined voltammetric peaks of Sudan I oxidation and lower overpotential compared with unmodified electrode. According to the results of differential pulse voltammetry (DPV), under optimized conditions, a good linear response was observed for the concentration of Sudan I in the range of 0.1–100.0 μM with a detection limit of 0.05 μM. The developed electrochemical sensor was successfully applied to determine Sudan I in water samples. This study indicated that NiFe2O4 nanoparticles based electrochemical sensor can be a promising and reliable tool for rapid analysis of Sudan I.

Bisphenol A (BPA) is an effective endocrine-disrupting compound (EDC) that causes adverse effects on human health and environment. This study reported a novel bisphenol A sensor via MnO2 nanorods modified screen printed electrode. The prepared MnO2/SPE presented fast response, high sensitivity and low background current. Differential pulse voltammetry (DPV) was used as an analytical method for the quantitative determination of bisphenol A, and the fabricated electrochemical sensor exhibits a linear response to bisphenol A in the range of 1.0–300.0 μM with the limit of detection (LOD) of 0.5 μM at a signal-to-noise ratio of 3. The prepared MnO2/SPE has been successfully used for detecting bisphenol A in water samples.

Levodopa, one of the prescribed medications in Parkinson disease, is electrochemically determined here. A Cu/TiO2 nanocomposite/room temperature ionic liquid/2-(ferrocenylethynyl)fluoren-9-one modified carbon paste electrode (Cu/TiO2-IL- 2FF/CPE) was used for the electrochemical determination of levodopa. The electro oxidation mechanism of levodopa at Cu/TiO2-IL-2FF/CPE was also studied. The obtained data showed that the electro-oxidation of levodopa at the Cu/TiO2-IL-2FF/CPE is greatly facilitated, which is attributed to high electrical conductivity of Cu/TiO2 nanocomposite, room temperature ionic liquid and 2-(ferrocenylethynyl)fluoren-9-one. The Cu/TiO2-IL-2FF/CPE showed a good electron mediating behavior followed by well separated oxidation signals of levodopa and tyrosine. Differential pulse voltammetric peak current showed a linear relationship corresponds to the concentrations of levodopa in a linear range of 0.03 to 700.0 μM with detection limit of 12.0 nM. The Cu/TiO2-IL-2FF/CPE shows excellent ability to determination of levodopa and tyrosine in real samples.

In this study, a new modified electrode was proposed to measure ascorbic acid. Graphite screen printed electrode was modified with NiFe2O4 nanoparticles (NiFe2O4/SPE). Cyclic voltammetry (CV), Chronoamperometry (CHA) and differential pulse voltammetry (DPV) methods were used to analyze the prepared electrode. The catalytic property resulting from the synergistic effect of this modifier not only increased the oxidation current but also reduced the oxidation potential of ascorbic acid. Scan rate and pH effects on the performance of NiFe2O4/SPE were also investigated. The linear calibration curve of ascorbic acid was obtained within the linear range of 5.0×10−7–1.0×10−4 M, and the detection limit was calculated as 1.0×10−7 M. Finally, the modified electrode was successfully used to measure ascorbic acid in some real samples.

Electrochemical behaviors of carbidopa at the surface of the graphite screen printed electrode (SPE) modified with Cu(II) nanocomplex, [CuCl2(salophen)]. H2O (salophen=o-phenylenediaminebis(salicylidenaminato)) were studied. The oxidation peak potential of the carbidopa at a surface of Cu/SPE appeared at 360 mV that was about 100 mV lower than the oxidation peak potential at the surface of the traditional SPE under similar condition. On other hand, the oxidation peak current was increased for about two times at the surface of Cu/SPE compared to SPE. The linear response range and detection limit were found to be 0.5-700 μM and 0.1 μM, respectively. The proposed sensor was successfully applied for the determination of carbidopa in real samples.

A novel modified graphite screen printed electrode (SPE) is prepared as an electrochemical sensor for determination of levodopa. The experimental results suggest that a screen printed electrode (SPE) modified with Cu(II) nanocomplex, [CuCl2(salophen)].H2O (salophen= o-phenylenediaminebis(salicylidenaminato)), accelerates the electron transfer reactions of levodopa. The fabricated sensor revealed some advantages such as convenient preparation, good stability and high sensitivity. The DPV data in 0.1 M phosphate buffer solution (PBS) (pH 7.0) allowed a method to be developed for the determination of levodopa concentrations in the ranges 5.0–900.0 μM, with the detection limits of 0.9 μM. The proposed method was successfully applied to determinations of levodopa in urine samples.

A sensitive electrochemical sensor for determination of hydroxylamine has been introduced. This sensor profits by 2-(4-Oxo-3-phenyl-3,4-dihydroquinazolinyl)-N′-phenylhydrazinecarbothioamide (2PHC) as mediator and magnetic core–shell Fe3O4@TiO2/MWCNT nanocomposite and ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) to improve the working electrode behavior. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry, and differential pulse voltammetry (DPV) are used to study of the suitability of 2PHC, at the surface of modified electrode, as a mediator for the electrocatalytic oxidation of hydroxylamine in aqueous solutions. The electrocatalytic peak current of hydroxylamine oxidation shows a linear dependence on hydroxylamine concentration in the range of 0.1–500.0 μM, by DPV in optimized conditions at pH 7.0. The detection limit (3σ) was obtained 52.0 nM. Electrochemical parameters such as electron transfer coefficient, α and diffusion coefficient, D, are also determined. The proposed method was successfully applied as a highly sensitive, selective, simple, and precise method for hydroxylamine determination in the water samples.

This work reports the voltammetric determination of epinephrine (EP) using ZnO-graphene oxide nanocomposite (ZnO-GO). The electrochemical behaviors of epinephrine at ZnO-GO nanocomposite modified graphite screen printed electrodes (SPE) were studied by cyclic voltammetry and differential pulse voltammetry. The outcomes confirmed that the proposed electrode demonstrate excellent electrocatalytic activity towards the oxidation of epinephrine in phosphate buffer solution (PBS, pH 7.0). The fabricated electrode possess lowest detection limit of 0.07 μM for epinephrine with the very wide dynamic linear range of 0.5 µM to 500.0 µM. Finally, the modified sensor was successfully implemented to detect epinephrine in epinephrine injection and urine samples.

A novel electrochemical sensor was proposed for the determination of amitriptyline based on the copper oxide (CuO) nanoparticles modified graphite screen-printed electrode. CuO nanoparticles were used to enhance the surface area of the electrode and then improve the sensitivity of the electrochemical sensor.
Amitriptyline electrochemical response characteristics of the modified electrode in a phosphate buffer solution (PBS) of pH 7.0 were investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The linear range for the detection of amitriptyline was changed from 1.0 µM to 200.0 μM with the detection limit of 0.4 μM (S/N=3). Finally, the proposed method was applied to measure amitriptyline in real samples. It was shown that the proposed sensor exhibited significant promise as a reliable technique for the detection of amitriptyline in real samples.

A Cu(II) nanocomplex, [CuCl2(salophen)].H2O [salophen=ophenylenediaminebis(salicylidenaminato)], was synthesized. The electrochemical properties of the as-prepared Cu(II) nanocomplex modified graphite screen printed electrode (Cu/SPE) were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Moreover, as a nanosensor for the determination of epinephrine the Cu/SPE exhibited excellent electrocatalytic activity for the oxidation of epinephrine with a faster electrontransfer rate. The DPV technique was used for the trace determination of epinephrine. The dependence of current vs. concentration was linear from 10.0 to 600.0 μM with a regression coefficient of 0.9975, and the detection limit of epinephrine was 2.5±0.05 μM. Finally, the method was applied to the selective and precise analysis of epinephrine in epinephrine injection.

A novel CdTe quantum dots is synthesized and used for modification of carbon paste electrode (QDMCPE). This modified electrode was used to study the electrooxidation of ascorbic acid using cyclic voltammetry (CV), square wave voltammetry (SWV) and chronoamperometry (CHA) as diagnostic techniques. SWV peak currents of ascorbic acid increased linearly with its concentrations in the range of 5.0×10-7-8.0×10-4 M with a detection limit of 3.0×10−7 M. The main objectives of QDMCPE for determination of ascorbic acid are: wide linear dynamic range, short time of the procedure and no use of electron transfer mediator.Finally this new sensor was used for determination of ascorbic acid in some real samples.

The direct electrochemistry of hypercin on a modified carbon paste electrode (CPE) was described. The electrode was modified with zinc oxide (ZnO) nanorods and nhexyl-3-methylimidazolium hexafluoro phosphate as a binder. The oxidation peak potential of hypercin at the surface of the ionic liquid / ZnO nanorods / CPE (ILZNCNPE) appeared at 320 mV, which was about 100 mV lower than the oxidation peak potential at the surface of the traditional carbon CPE under a similar condition. The linear response range and detection limit were found to be 2.5×10-6- 2.0×10-4 M and 9.1×10-7 M, respectively.

A carbon paste electrode modified with TiO2/Fe3O4/MWCNT nanocomposite and ionic liquids (TFMWCNT/IL/CPE) was employed for the simultaneous determination of ascorbic acid (AA) and tryptophan (TRP). The TFMWCNT/IL/CPE displayed excellent electrochemical catalytic activities toward AA and TRP oxidation compared with bare CPE. In the differential pulse voltammetry technique, both AA and TRP gave sensitive oxidation peaks at 270 and 700 mV respectively. Under the optimized experimental conditions, AA gave linear responses over range of 2.5 to 100.0 μM. The lower detection limit was found to be 1.13 μM for AA. The investigated method showed good stability, reproducibility, and repeatability for determination of AA and TRP in pharmaceutical samples.