Square-wave Adsorptive Anodic Stripping Voltammetry Research Articles

Electrochemical stripping voltammetrical sensor based on polypyrrole exfoliated polyetheramine-montmorillonite nanocomposite for nanomolar detection of nifuroxazide.

A series of polypyrrole/polyetheramine-montmorillonite nanocomposites have been fabricated by the intercalation of different types of polyoxyalkylene amine hydrochloride (Jeffamines: D400, D2000, T5000, and T403) into montmorillonite layers via the cation-exchange process followed by in situ polymerization of pyrrole. The physicochemical characteristics of as-prepared nanocomposites were investigated using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and electrochemical impedance spectroscopy (EIS) instruments. The change of the types of Jeffamine causes a change in the geometrical structure, and surface area of nanocomposites. Noteworthy, the resulting polypyrrole/D2000-montmorillonite ([PDM-50]) nanocomposite exhibited a cauliflower-like shape with a specific surface area (116.2 m2 g-1) with the highest conductivity. Furthermore, the modified stripping voltammetric carbon paste sensor was fabricated based on 1.0% [PDM-50] nanocomposites to detect the drug nifuroxazide (NF). The sensor achieved detection limits (LD) of 0.24, and 0.9 nM of NF in the medication, and human urine fluid, respectively. This sensor showed appropriate repeatability, reproducibility, stability, and selectivity for NF sensing in different fluids accompanied by other interferents.

Anatase titanium oxide nanoparticles and multi-walled carbon nanotubes-modified carbon paste electrode for simultaneous determination of avanafil and doxorubicin in plasma samples

Patients who receive anticancer drugs, might experience loss of sexual desire together with erectile dysfunction as one of cancer medications’ adverse effects. This might have a negative effect on their psychological functioning and quality of life and accordingly phosphodiesterase type 5 (PDE5) inhibitors as sex stimulants are used. One of the recently FDA-approved members of this class of drugs is avanafil (AVN) that is administered to assist in improving penile erection. Because of the seriousness of the cancer patient's health condition, it is mandatory to recognize the possible pharmacokinetic interactions in case of administering other drugs at the same time. Therefore, a sensitive sensor derived from carbon paste electrode (CPE) modified with anatase titanium dioxide nanoparticles (TiO2-NPs) and multi-walled carbon nanotubes (MWCNTs) was designed for the simultaneous determination of AVN and the anticancer drug doxorubicin (DOX) in spiked and real rabbit plasma samples. X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM) were employed to fully characterize the fabricated electrode. The modified electrode offers a considerable improvement in voltammetric sensitivity toward oxidation of AVN and DOX, compared to the bare electrode. A good separation was achieved between the oxidation peak potentials of AVN (1.4 V) and DOX (0.8 V). The effect of different voltammetric parameters on the peak separation and sensitivity for both drugs was studied to select the optimum experimental conditions. It was found that the optimum pH for the simultaneous determination of both drugs was obtained utilizing a Britton-Robinson buffer (BR) of pH 3.0. Furthermore, the electrochemical oxidation of AVN and DOX was evaluated with different modified carbon paste electrodes using cyclic voltammetry (CV) and square-wave adsorptive anodic stripping voltammetry (SWAdASV). The analytical curves for the quantitative simultaneous determination of AVN and DOX exhibited acceptable linearity within the concentration range from (0.10–6.0 μmol L−1 for AVN) and (5.0–35.0 μmol L−1 for DOX) in spiked rabbit plasma. Detection and quantitation limits were determined to be 0.035 and 0.10 μmol L−1 in the case of AVN and 1.3 and 4.0 μmol L−1 in the case of DOX, respectively. The method was effectively applied for the analysis of AVN in real rabbit plasma samples after the coadministration of DOX. Moreover, the proposed voltammetric method was useful as a therapeutic drug monitoring method to investigate the possible pharmacokinetic interactions between AVN and DOX in real rabbit plasma. An increase in the level of AVN in rabbit plasma was observed after administering DOX, and accordingly, the dose of AVN should be adjusted and monitored.

Fabrication of an electrochemical sensor based on gold nanoparticle-functionalized nanocarbon black hybrid nanocomposite for sensitive detection of anti-cancer drug formestane in biological and pharmaceutical samples

• A novel Au@f-NCB hybrid nanocomposite was successfully synthesized and characterized. • The Au@f-NCB modified MW-GCPE exhibited superior performance toward electrosensing of FMST with high sensitivity. • The new sensor was used successively for analysis of FMST in biological fluids, Lentaron depot ampoules and plasma of patient. • Electrosensing of FMST in the presence of anticancer drug DOX was explored. A gold nanoparticle decorated functionalized nanocarbon black (Au@f-NCB) hybrid nanocomposite–modified molecular wire glassy carbon paste electrode (MW-GCPE) was constructed for sensitive determination of anticancer drug formestane (FMST) by square-wave adsorptive anodic stripping voltammetry (SW-AASV). The synthesized Au@f-NCB hybrid nanocomposite was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and dispersive X-ray spectroscopy (EDX). The fabricated Au@f-NCB/MW-GCPE was found to have higher electrocatalytic activity towards the oxidation of FMST than bare GCPE. The developed electrochemical sensor allowed the ultrasensitive and selective detection of FMST with a linear range (0.02–5.2 µM), low limit of detection (7.14 nM), and high sensitivity (90.0 μA μ M −1 cm −2 ). The constructed Au@f-NCB nanocomposite modified MW-GCPE revealed good repeatability, reproducibility, and higher stability. Furthermore, the developed sensor has been shown to be highly sensitive for detecting FMST in human fluids, Lentaron depot ampoules, and patient plasma. In addition, electrosensing of FMST in the presence of the anti-cancer chemotherapy drug doxorubicin (DOX) was explored, and simultaneous detection of the two drugs was achieved.

Advanced sensing platform for nanomolar detection of food preservative nitrite in sugar byproducts based on 3D mesoporous nanorods of montmorillonite/TiO2–ZnO hybrids

Nitrite (NO2−) pollution pose hazards to human health. NO2− oxidizes haemoglobin to methaemoglobin, thereby minimizing the oxygen-conveying capacity. Herein, we synthesized three-dimensional (3D) mesoporous nanorods (MNRs) of peeled montmorillonite (MMT)/TiO2–ZnO hybrid modulated sensors as a robustly sensitive electrochemical sensor for detecting NO2− using the square-wave adsorptive anodic–stripping voltammetry. The 3D mesoporous nanorods of coupled TiO2–ZnO composite [TZ] and series of MMT/TiO2–ZnO hybrids were synthesized using various contents of MMT [MTZ1-4] MNRs via a sol–gel method. Varying the weight percentage of MMT exhibited remarkable effects including changing of the geometrical structure, superficial area, and degree of porosity. Notably, [MTZ2] with 1.0% of MMT exhibited the most structured MNR morphology and best superficial area (77.6 m2/g) with minimal resistivity. Cyclic voltammetry revealed that the developed modulated sensor with 1.0% [MTZ2] MGPS preserved a remarkable electrocatalytic activity as evaluated from the cyclic voltammetry (CV) mensuration. Under optimal operating conditions, the proposed sensor achieved a linearity range of 0.04–10 nM and a limit of detection of 0.12 nM for NO2− with sensitivity (0.78 μA.nM−1). It also achieved good accuracy, precision, and high selectivity for detecting NO2− in food preservatives such as sugar byproducts (molasses products).

Graphite Studded with Facile-Synthesized Cu2O Nanoparticle-Based Cubes as a Novel Electrochemical Sensor for Highly Sensitive Voltametric Determination of Mebeverine Hydrochloride

Herein, a feasible chemical reduction method followed by intensive mixing was applied for the preparation of an attractive material based on graphite studded with cuprous oxide nanoparticle-based cubes (Cu2ONPs–C@G). Transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV) were utilized for characterization. Cuprous oxide nanoparticles (Cu2ONPs), with a diameter range mainly distributed from 4 to 20 nm, aggregate to form microcubes (Cu2ONPs–C) with an average diameter of about 367 nm. Paste electrode was prepared using Cu2ONPs–C@G (Cu2ONPs–C@G/PE) for voltametric quantification of the musculotropic antispasmodic drug: mebeverine hydrochloride (MEB). The electrochemical behavior of MEB was studied using CV, and the optimum analytical parameters were investigated using square wave adsorptive anodic stripping voltammetry (SWAdASV). Moreover, density functional theory (DFT) was used to emphasize the ability of MEB to form a complex with Cu2+, confirming the suggested electrochemical behavior of MEB at Cu2ONPs–C@G/PE. With good stability and high reproducibility, SWAdASV of Cu2ONPs–C@G/PE shows successful quantification of MEB over the concentration range of 5.00 × 10−11–1.10 × 10−9 M with lower limit of detection (LOD) and lower limit of quantification (LOQ) values of 2.41 × 10−11 M and 8.05 × 10−11 M, respectively. Finally, accurate quantification of MEB in dosage forms (tablets) and biological fluids (spiked human urine and plasma samples) was achieved using Cu2ONPs-C@G/PE.

Fabrication and characterization of extrinsic electrochemically modified graphite reinforcement carbon paste electrode for selective determination of Cu(II) in trace levels

An electrochemical oxidation of copper species has been successfully performed by using electrochemically modified 8‑hydroxy quinoline graphite reinforcement carbon paste electrode; in other words, quinolyl graphite reinforcement Carbon paste electrode (Q/GRCPE). Scanning electron microscopy (SEM) was used for the morphological characterization of the electrode before the modification and after modification and utilization. Under the optimal conditions of cyclic voltammetry (CV) and square wave adsorptive anodic stripping voltammetry (SWAdASV), the electrochemical oxidation of Cu(II) can be investigated. The performance of the electrochemically modified sensor was systematically studied. The experimental data suggested that the electrochemically modified sensor exhibited excellent catalytic activity for the electrochemical oxidation of Cu(II) with a detection limit (LOD) 2.1 × 10−11 M. The application of the electrochemically modified sensor for the detection of Cu(II) in Tap water (TW), ground water (GW) and Nile River water (NRW) showed good recovery with reproducible results. The peak currents of Cu(II) were evaluated within a wide concentration range, in favor of more durability, sensitivity, and selectivity which suitable for investigation of real samples. It was shown that the proposed electrochemically modified Q/GRCPE proved to be a cheap "pre- alarm" tool for rapid determining of Cu(II) in environmental water samples even in the presence of some interfering ions. The adsorptive accumulation of Cu(8-HQ)2, approaches results in an effective preconcentration of Cu(II) with short adsorption time (30 s).

Electrochemical sensor based on ionic liquid and carbon black for voltammetric determination of Allura red colorant at nanomolar levels in soft drink powders

The ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate and carbon black (CB) nanoparticles were incorporated within a crosslinked chitosan film over the surface of a glassy carbon electrode, and the obtained architecture explored to the sensitive voltammetric sensing of Allura red colorant in soft drinking powders. The different electrodic surfaces were morphologically and electrochemically characterized. From the modification of glassy carbon electrode with IL and CB, a significantly enhanced voltammetric response was achieved toward the Allura red irreversible oxidation reaction. The type and amount of IL employed in the electrode modification step as well as all the others experimental parameters affecting the sensor response by square-wave adsorptive anodic stripping voltammetry (SWAdASV) were systematically optimized. Under the optimum experimental conditions, the proposed SWAdASV procedure provided a linear analytical curve in the concentration range of 3.98 × 10−8 to 9.09 × 10−7 mol L−1 and a low limit of detection of 9.1 × 10−10 mol L−1 (0.91 nmol L−1). The proposed sensor presented good precision and no matrice effects as shown from repeatability tests, concomitant studies and addition/recovery assays. The developed SWAdASV procedure was applied successfully in the determination of Allura red content in commercial soft drink powder samples, and the results were in close agreement with those obtained using a comparative spectrophotometric method at a confidence level of 95%.

Electrochemical sensors based on biomimetic magnetic molecularly imprinted polymer for selective quantification of methyl green in environmental samples.

A new biomimetic sensor was prepared on carbon paste with magnetic molecularly imprinted polymer (mag-MIP) for sensitive and selective detection of methyl green dye. The mag-MIP was synthesized using a functional monomer that was selected before by computational simulation. A mag-NIP (magnetic non-imprinted polymer) control material was also prepared for comparative purposes. Modeling adsorption studied revealed that the dye-polymer interface followed pseudo-first order kinetics and that maximum adsorption (Qm) of the dye on mag-MIP was 3.13 mg g-1, while the value for mag-NIP was 1.58 mg g-1. The selective material was used as a sensing spot in fabrication of an electrochemical sensor based on modified carbon paste. For electrochemical analysis, the best achievement of the sensor was acquire by tack together a paste with 6.7% (w/w) of mag-MIP and using square-wave adsorptive anodic stripping voltammetry (SWAdASV) in 0.1 mol L-1 phosphate buffer (pH 7.0), with an applied potential (Eappl) of 0.3 V vs. Ag|AgClsat during an adsorption time (Tads) of 120 s. The results were obtained under optimized conditions in which sensor provided a linear concentration range of methyl green from 9.9 × 10-8 to 1.8 × 10-6 mol L-1, with a limit of detection (LOD) of 1.0 × 10-8 mol L-1 and a satisfactory relative standard deviation (RSD) of 4.3% (n = 15). The proposed sensor was applying using two spiked river water samples, obtaining recoveries ranging from 93% to 103%. The proposed method exhibits excellent precision also high reliability and proved to be an alternative method for the quantification of methyl green in real samples.

Development of a new electrochemical sensor based on silver sulfide nanoparticles and hierarchical porous carbon modified carbon paste electrode for determination of cyanide in river water samples

In this study, a new electrochemical sensor for determination of cyanide is proposed. The sensor is formed by a carbon paste electrode modified with hierarchical porous carbon and silver sulfide nanoparticles. The morphology characterization was performed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), while the chemical and electrochemistry characterization were performed by energy dispersive X-ray spectroscopy and cyclic voltammetry, respectively. Under the optimized conditions, the Ag2SNPs-HPC300 sensor presented a large concentration linear range of 5.9 × 10−7 to 1.1 × 10-3 mol L-1, and limit of detection of 7.0 × 10-8 mol L-1 using square-wave adsorptive anodic stripping voltammetry (SWAdASV) technique. The analytical response of the Ag2SNPs-HPC300 sensor was evaluated in presence of different compounds, and the results showed a RSD of 4.3% in triplicate experiments. The applicability of the Ag2SNPs-HPC300 sensor in river water samples contaminated with cyanine showed recoveries values near 100%. The developed method exhibited high sensitivity and selectivity, good reproducibility, repeatability and low-cost, demonstrating to be a very promising analytical alternative for determination of cyanide in this matrix.

Square-wave adsorptive anodic stripping voltammetric determination of norfloxacin using a glassy carbon electrode modified with carbon black and CdTe quantum dots in a chitosan film.

A glassy carbon electrode was modified with carbon black and CdTe quantum dots in a chitosan film to obtained a sensor for norfloxacin (NOR) in the presence of dopamine, caffeine, and uric acid. The morphological, structural and electrochemical characteristics of the nanostructured material were evaluated using spectrophotometry, X-ray diffraction, transmission electronic microscopy and voltammetry. The high electrochemical activity, fast electron transfer rate and high surface area enhanced the oxidation peak currents and shifted the peak potentials of NOR for more negative values (typically at 0.95V vs. Ag/AgCl). Electrochemical determination of NOR was carried out using square-wave adsorptive anodic stripping voltammetry (SWAdASV). Response is linear in the0.2 to 7.4μmolL-1 NOR concentrationrange, and the detection limit is as low as 6.6nmolL-1. The method was successfully applied to the determination of norfloxacin in pharmaceutical formulation, synthetic urine and spiked serum. Graphical abstract Schematic presentation of a voltammetric method using a glassy carbon electrode modified with carbon black and CdTe quantum dots in a chitosan film for the determination of norfloxacin in serum and urine samples.

A Green Method for the Determination of Mebeverine in Its Pharmaceutical Products and Human Serum Based On Diatom Modified Carbon Paste Electrode Using Square Wave Adsorptive Anodic Stripping Voltammetry (SW-AdASV)

AbstractThe first use of a green method of analysis using diatom for trace determination of mebeverine in its pharmaceutical formulation and human serum based on its great properties such as high surface area, hydrophilicity, and adsorption. in addition to diatom requires no chemical modification. Characterization of Diatom using FTIR showed bands corresponding to AlMgOH, Si-O-Al, SiOH, and OH, while XRD showed that diatom is amorphous containing silica of quartz crystal shape, SEM revealed that diatom has porous surface. Cyclic Voltammetry of the modified electrode revealed that the modified electrode has higher surface area and greater adsorption. Mebeverine hydrochloride (MV.HCl) was determined based on 5% diatom modified carbon paste electrode 5% (w/w)DA/CPE as a sensor with LOD and LOQ of 1.80×10−9 and 6.00×10−9 respectively. Then, the modified electrode was successfully applied for the trace determination of MV.HCl in different pharmaceutical preparations; “Coloverin A”, “Colona” and “Colofac” tablets without interferences from excipients and co-formulated drugs. The achieved detection limit in human serum was 8.0×10−9 M. The described adsorptive anodic stripping voltammetric method is reliable, simple, and sensitive enough for assay of MV.HCl in real plasma samples, pharmacokinetic studies, quality control and assurance of the drug in industry and in clinical laboratories.

Sensitive voltammetric determination of hydroxyzine and its main metabolite cetirizine and identification of oxidation products by nuclear magnetic resonance spectroscopy

The electrochemical detection and electrooxidation path of the first-generation antihistamine receptor hydroxyzine (HDZ) and its main metabolite cetirizine (CTZ) are addressed in this research. A carbon black-modified electrode to explore the electrochemical responsivity and electroanalytical detection of HDZ and CTZ was designed. Compared to the bare electrode, the irreversible anodic responses observed for HDZ and CTZ were considerably improved on the proposed carbon black-modified electrode, including twenty times enhancement of the anodic peak currents and the shifting of anodic peak potentials to less positive potentials. In order to identify the electrooxidation products resulting from the previously verified irreversible redox processes, cyclic voltammetric studies and potentiostatic electrolysis assays followed by products identification by nuclear magnetic resonance (NMR) spectroscopy were carried out. From the combination of electrochemistry and NMR spectroscopy data it was possible to propose electrooxidation reaction mechanisms for HDZ and CTZ molecules. By applying square-wave adsorptive anodic stripping voltammetry (SWAdASV) under optimized experimental conditions, the obtained analytical curves for HDZ and CTZ were linear from 2.99×10−7 to 9.81×10−6molL−1 and from 4.97×10−7 to 1.08×10−5molL−1, with limits of detection of 1.00×10−7molL−1and 4.00×10−7molL−1, respectively. Finally, spiked synthetic human biological fluids were analysed by the proposed SWAdASV procedures, with recovery percentages close to 100%.

Fabrication of biosensor based on Chitosan-ZnO/Polypyrrole nanocomposite modified carbon paste electrode for electroanalytical application

A sensitive conductive nanocomposite sensor consisting of chitosan, zinc oxide nanoparticles, and polypyrrole was developed. The sensor was prepared by oxidative polymerization of pyrrole using (NH4)2S2O8 as the oxidant followed by mixing a Chitosan-Zinc oxide composite with a different content of Chitosan. The morphology and surface area of the nanocomposites were changed by changing the percentage of chitosan. The newly developed nanocomposites also showed a significant improvement in electrical conductivity as mentioned from the cyclic voltammetry measurements of the K3[Fe(CN)6] sample. A square-wave adsorptive anodic stripping voltammetry method successfully measured Isoxsuprine hydrochloride using different types of nanocomposite modified CPEs and showed a large enhancement of stripping peak current compared to bare CPE. Consequently, the proposed sensors proved to have a promissing feature for applications in biosensors.

Trace Determination of Duloxetine HCl in Formulation and Spiked Human Serum at a Carbon Paste Electrode

The electrochemical behavior of duloxetine HCl (DXT.HCl) at a carbon paste electrode (CPE) was achieved by cyclic voltammetry and a mechanism of its oxidation was reported and illustrated. A sensitive linear sweep and square-wave adsorptive anodic stripping voltammetry methods were described for trace determination of DXT.HCl. Introduction: DXT.HCl, N-methyl-3-(nap-thalen-1- yloxy)-3-(thiophene-2-yl) propan-1-amine hydrochloride is a selective serotonin-norepinephrine reuptake inhibitor (SNRI) originally developed as an antidepressant and is currently recommended for maintenance treatment of major depressive disorder. Methods: Electrochemical behavior was studied using cyclic voltammetric method, and the analytical application was studied using linear sweep and square wave voltammetric methods. Solution pH has been measured by pH meter. Results: The process on the surface of carbon paste electrode was found to be irreversible and diffusion-controlled. The number of proton and electron transferred were calculated. Possible reaction mechanism taking place on the surface of electrode was proposed. Calibration plot constructed using square wave voltammetric technique was used for quantitative analysis in pharmaceutical and human serum samples. Limit of detection (LOD) and limit of quantification (LOQ) were calculated. Conclusions: In the present work, we described the electrochemical behavior of DXT.HCl drug. Two precise linear sweep and square wave adsorptive anodic stripping voltammetry methods have been described for its trace quantitation in pharmaceutical formulation and human serum. The method shows the development of a sensor for selective and sensitive determination of DXT.HCl.

Electrochemical sensor based on graphene oxide and ionic liquid for ofloxacin determination at nanomolar levels

New insights into the design of highly sensitive, carbon-based electrochemical sensors are presented in this work by exploring the interesting properties of graphene oxide (GO) and ionic liquids (ILs). An electrochemical sensor based on the carbon paste electrode (CPE) modified with GO and IL was developed for the sensitive detection of ofloxacin using square-wave adsorptive anodic stripping voltammetry (SWAdASV). GO sheets were obtained from the acid treatment of graphene and characterized by scanning and transmission electronic microscopy (SEM and TEM) and selected area electron diffraction (SAED), and the electrochemical behavior of the modified GO-IL/CPE was explored by electrochemical impedance spectroscopy studies. The CPE modification with GO and IL allowed an 8.2 fold increase in the analytical sensitivity for ofloxacin sensing compared to the unmodified CPE. Under the optimized experimental conditions using the SWAdASV technique, the GO-IL/CPE sensor provided an analytical curve for ofloxacin in the concentration range of 7.0×10−9 to 7.0×10−7molL−1, with a sensitivity of 7.7×106μALmol−1 and limit of detection of 2.8×10−10molL−1 (0.28nmolL−1). The proposed sensor was successfully applied for the ofloxacin determination in human urine and ophthalmic samples, with recoveries near 100%. The results were similar those obtained by a spectrophotometric comparative method.

Graphene/Nafion composite film modified glassy carbon electrode for simultaneous determination of paracetamol, aspirin and caffeine in pharmaceutical formulations

A graphene-Nafion composite film was fabricated on the glassy carbon electrode (GR-NF/GCE), and used for simultaneous determination of paracetamol (PAR), aspirin (ASA) and caffeine (CAF). The electrochemical behaviors of PAR, ASA and CAF were investigated by cyclic voltammetry and square-wave adsorptive anodic stripping voltammetry. By using stripping one for simultaneous determination of PAR, ASA and CAF, their electrochemical oxidation peaks appeared at +0.64, 1.04 and 1.44V, and good linear current responses were obtained with the detection limits of 18ngmL−1 (1.2×10−9M), 11.7ngmL−1 (6.5×10−8M) and 7.3ngmL−1 (3.8×10−8M), respectively. Finally, the proposed electrochemical sensor was successfully applied for quantifying PAR, ASA and CAF in commercial tablet formulations.

Electrochemical determination of pterostilbene at a cathodically pretreated boron-doped diamond electrode using square-wave adsorptive anodic stripping voltammetry in cationic surfactant media

In the present paper, an electrochemical method was developed for the determination of pterostilbene (a phenolic phytoalexin) using adsorptive anodic stripping voltammetry at a cathodically pretreated boron-doped diamond electrode. The oxidation of compound was irreversible and exhibited an adsorption controlled process which is of pH dependence. The sensitivity of the stripping voltammetric measurements was significantly improved in the presence of cationic surfactant, cetyltrimethylammonium bromide (CTAB). Using square-wave stripping mode, a highly linear analytical curve was obtained for pterostilbene determination in 0.1M HNO3 solution containing 2×10−4M CTAB at +0.78V (vs. Ag/AgCl) (after 30s accumulation at open-circuit condition). The process could be used in the range of 0.005–1.0μgmL−1 (2.0×10−8–3.9×10−6M), with a detection limit of 0.0011μgmL−1 (4.3×10−9M). The proposed method was successfully applied to measure the concentration of pterostilbene in the commercial dietary supplements, with results similar to those obtained using a HPLC method at 95% confidence level. As far as it could be verified, the proposed method is the first one based on the electrochemical investigation of pterostilbene.

A new sensor architecture based on carbon Printex 6L to the electrochemical determination of ranitidine

A glassy carbon electrode (GCE) modified with carbon Printex 6L (Printex6L/GCE) as a novel sensor is proposed. A morphological study was carried out using scanning electron microscopy, and an electrochemical characterization of the proposed electrode was performed by cyclic voltammetry (CV) using [Fe(CN)6]4− as a redox probe. With the incorporation of the carbon Printex 6L film onto the GCE surface, the [Fe(CN)6]4− analytical signal was substantially increased and the difference between the oxidation and reduction potentials (ΔE p) decreased, a characteristic of the electrocatalytic effect. Furthermore, the use of carbon Printex 6L film resulted in an 84 % increase in the oxidation current and a 123 % increase in the reduction current. Faster charge transfer was observed at the proposed electrode/electrolyte interface during CV when compared with GCE. The Printex6L/GCE was tested for ranitidine (RNT) sensing and showed a decrease in the working potential and an increase in the analytical signal, when compared with GCE, again demonstrating an electrocatalytic effect. Under optimized experimental conditions, the developed square-wave adsorptive anodic stripping voltammetry (SWAdASV) method presented an analytical curve that was linear in RNT concentration range from 1.98 × 10−6 to 2.88 × 10−5 mol L−1 with a detection limit of 2.44 × 10−7 mol L−1. The developed Printex6L/GCE was successfully applied to the determination of RNT concentrations in human body fluid samples (urine and serum).

Nano Determination of Kinase Inhibitor Sorafenib Drug in Pharmaceutical Formulation and Human Blood at a Modified Carbon Paste Electrode

Sorafenib (SORA) has clinical activity against several tumor types. Carbon paste electrode modified with natural sodium montmorillonite clay (Na-MMT/CPE) was used as a sensor for sensitive and selective determination of SORA drug using square-wave adsorptive anodic stripping voltammetry (SW-AdASV). Unmodified CPE as well as the modified one were characterized using scan electron microscopy (SEM), N2 sorption isotherms (BET) and electrochemical impedance spectra (EIS). In spite of the very low conductivity of Na-MMT, a shift in the peak potential to less positive and about two times enhancement in the peak current were observed at 5% (w/w) Na-MMT/CPE compared to that at bare CPE, reflecting electrocatalytic activity of Na-MMT toward oxidation of SORA. This may be attributed to strong adsorptive property of Na-MMT due to its high surface area or specific bonding reactions of SORA with the functional groups at the edges of clay sheets. The method was employed successfully to determine SORA in its pharmaceutical formulation (Nexavar tablets). Detection limit of 1.5 × 10−10 M was also achieved in human serum. The described method is reliable, simple and sensitive enough for assay of SORA in real plasma samples, pharmacokinetic studies, quality control and assurance of the drug in industry and in clinical laboratories.

Electrochemical determination of rosuvastatin calcium in pharmaceutical and human body fluid samples using a composite of vertically aligned carbon nanotubes and graphene oxide as the electrode material

A novel electrochemical method for the determination of rosuvastatin calcium (RC) using a composite of vertically aligned carbon nanotubes and graphene oxide (VACNT-GO) as the electrode material is proposed. The VACNT-GO electrode was synthesized using a microwave-assisted chemical vapor deposition method followed by oxygen plasma treatment. The VACNT-GO electrode presented superhydrophilic behavior and fast charge transfer, which are very attractive for electrochemical applications. The RC molecule presented an oxidation process at +1.26V vs. Ag/AgCl (3.0molL−1 KCl) in phosphate buffer solution (pH 2), and this redox behavior was explored for its voltammetric determination. Using square-wave adsorptive anodic stripping voltammetry (SWAdASV) under optimized conditions, the analytical curve was linear in RC concentration range from 0.48 to 46.72μmolL−1 with a limit of detection of 0.06μmolL−1. The developed SWAdASV method was applied for RC quantification in commercial pharmaceutical samples, and the results are consistent with those obtained by the comparative spectrophotometric method at a confidence level of 95%. Moreover, RC was determined in human body fluid samples of urine and human serum.