Enhanced Supercapacitor Performance Using a Co3 O4 @Co3 S4 Nanocomposite on Reduced Graphene Oxide/Ni Foam Electrodes.

To avoid an enormous energy crisis in the not-too-distant future, it be emergent to establish high-performance energy storage devices such as supercapacitors. For this purpose, a three-dimensional (3D) heterostructure of Co3 O4 and Co3 S4 on nickel foam (NF) that is covered by reduced graphene oxide (rGO) has been prepared by following a facile multistep method. At first, rGO nanosheets are deposited on NF under mild hydrothermal conditions to increase the surface area. Subsequently, nanowalls of cobalt oxide are electro-deposited on rGO/Ni foam by applying cyclic-voltammetry (CV) under optimized conditions. Finally, for the synthesis of Co3 O4 @Co3 S4 nanocomposite, the nanostructure of Co3 S4 was fabricated from Co3 O4 nanowalls on rGO/NF by following an ordinary hydrothermal process through the sulfurization for the electrochemical application. The samples are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained sample delivers a high capacitance of 13.34 F cm-2 (5651.24 F g-1 ) at a current density of 6 mA cm-2 compared to the Co3 O4 /rGO/NF electrode with a capacitance of 3.06 F cm-2 (1230.77 F g-1 ) at the same current density. The proposed electrode illustrates the superior electrochemical performance such as excellent specific energy density of 85.68 W h Kg-1 , specific power density of 6048.03 W kg-1 and a superior cycling performance (86% after 1000 charge/discharge cycles at a scan rate of 5 mV s-1 ). Finally, by using Co3 O4 @Co3 S4 /rGO/NF and the activated carbon-based electrode as positive and negative electrodes, respectively, an asymmetric supercapacitor (ASC) device was assembled. The fabricated ASC provides an appropriate specific capacitance of 79.15 mF cm-2 at the applied current density of 1 mA cm-2 , and delivered an energy density of 0.143 Wh kg-1 at the power density of 5.42 W kg-1 .

Determination of Bromate Ions in Drinking Water by Derivatization with 2-Methyl-2-Butene, Dispersive Liquid-Liquid Extraction and Gas Chromatography-Electron Capture Detection.

BACKGROUND: A simple, rapid, selective and sensitive sample preparation and derivatization method was performed for determination of bromate ions in water by means of dispersive liquid-liquid extraction (DLLE) by gas chromatography-electron capture detection (GC-ECD). This method is based on 2-methyl-2-butene derivatization by bromine produced from bromate ions in acidic medium and extraction by n-hexane. OBJECTIVE: Derivatizing agent: It is cheap and available and it has high efficiency in reaction with Br2. Simplicity: Preparation and extraction process don't need to any specific equipment and procedure is completely simple and fast. Limit of detection: DL is as low as 0.43 µg/L. METHODS: Various effective factors on the derivatization and extraction efficiency, such as amount of derivatizing agent, volume of extraction solvent, bromide concentration, volume and concentration of sulfuric acid, type and volume of extracting and dispersing solvent, ionic strength, storage time before extraction and ECD makeup-gas flow rate were investigated. RESULTS: Under the optimum conditions, the method had a linear calibration curve ranging from 1.0 to 200.0 µg/L for bromate ions with a determination coefficient (R2) of 0.994 and the detection limit was 0.43 µg/L. The recovery percent and relative standard deviation for the determination of 1.0, 5.0 and 50.0 µg/L bromate ion was between 90 and 110%, and 3.0 and 8.0% (n = 3), respectively. CONCLUSIONS: Finally, the method was successfully applied for the preconcentration and determination of bromate ions in water samples, and satisfactory results were obtained. HIGHLIGHTS: (1) Fast, easy, accurate and economical innovative analysis of bromate ions in water and wastewater. (2) Determination of inorganic ion by GC-ECD after derivatization (3) Low detection limit (4) Optimization of different method parameters to obtain accurate results based on requirements of international standards, specifically ISO/IEC 17025.

Bio-based Fe3O4/chitosan nanocomposite sensor for response surface methodology and sensitive determination of gallic acid.

In this study, preparation of a novel bio-sensor based on Fe3O4/chitosan nanocomposites reported for electrochemical studies and determination of gallic acid (GA). Combination of chitosan with Fe3O4 nanoparticles causes to improve oxidation current of the GA. Characterization of the nanocomposite is carried out by different techniques such as X-ray diffraction, transmission electron microscopy, scanning electron microscopy, vibrating sample magnetometer, electrochemical impedance spectroscopy and cyclic voltammetry. Furthermore, multivariate optimization strategy is applied for simultaneous optimization of the chemical and instrumental parameters. Moreover, electrochemical behavior of GA at the surface of the nano-structured sensor is studied by various techniques such as chronoamperometry, chronocoulometry and linear sweep. Using these techniques, the diffusion coefficient (D = 5.05 × 10-4 cm2 s-1 and or 4.86 × 10-4 cm2 s-1), and the kinetic parameters containing the exchanging current density (j0 = 0.23 µA cm-2) and electron transfer coefficient (α = 0.1) are determined for GA, respectively. Then, the detection limit for GA is found to be 12.1 nM with a broad linear dynamic range 0.5-300.0 µM using differential pulse voltammetry DPV at the surface of the Fe3O4/chitosan sensor. Finally, the proposed method is successfully applied for the detection of the analyte in real samples.

Multivariate optimization methods for in-situ growth of LDH/ZIF-8 nanocrystals on anodized aluminium substrate as a nanosorbent for stir bar sorptive extraction in biological and food samples.

In-situ growth of zeolite imidazolate frameworks (ZIFs) on the surface of layered double hydroxides (LDHs) for preparation of porous nanocomposites is a favorable strategy to design potential materials in separation fields. In this research, nanoporous Zn-Al LDH/ZIF-8 composite was prepared by in-situ growth of ZIF-8 on the Zn-Al LDH surface. The nanocomposite was applied for stir bar sorptive extraction and detection of benzylpenicillin (penicillin G, PEN G). Characterizations of the nanocomposite were performed by various techniques, including Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and thermogravimetric differential thermal analysis. An optimized strategy based on response surface methodology was combined with high performance liquid chromatography analysis. Under the optimized conditions, the limit of detection and quantification obtained were 0.05 and 0.15 µg l-1, respectively. The good validation criteria results allowed the method to be used in the quantification of PEN G in real samples.

Chemometrics-assisted determination of Sudan dyes using zinc oxide nanoparticle-based electrochemical sensor.

Multivariate curve resolution-alternating least squares (MCR-ALS) assisted with electrochemical techniques was applied for simultaneous determination of Sudan II and III at a surface of zinc oxide nanoparticles (ZnONPs) modified carbon paste electrode. Characterization of the ZnONPs and the nanostructured modified electrode was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Response surface methodology using central composite rotatable design was employed to design of experiments and achieving to optimum values of variables. For simultaneous determination of Sudan II and III, electrochemical second order data were obtained by changing of pulse height in differential pulse voltammetry technique. MCR-ALS was performed on the data to obtain the decomposition peaks of analytes. Then, the detection limits were obtained 1.87 and 2.62 nM for Sudan II and III, respectively. Finally, this method used for the analysis of the two analytes in real samples.

Gas chromatography-mass spectrometry analysis and antimicrobial, antioxidant and anti-cancer activities of essential oils and extracts of Stachys schtschegleevii plant as biological macromolecules.

This work reports the chemical composition and antimicrobial activity of the essential oil as well as antioxidant and anti-cancer activities of ethyl acetate and aqueous extracts from leaf and stem of Stachys schtschegleevii. The structure of volatile parts and effective phenolic compounds as biological macromolecules as well as biological activity of the Stachys schtschegleevii plant were studied using various methods. Essential oils of stem and leaf were identified by steam distillation method and characterization was performed using a gas chromatography-mass spectrometry (GC-MS) analysis. Anti-microbial activity of extracted macromolecules from essential oils of two ethyl acetate and aqueous parts of stem and leaf were analyzed by minimal inhibition concentration (MIC) method. The crude extracts exhibited no appreciable antioxidant activities, in 2,2-diphenyl-1-picrylhydrazyl (DPPH) test by IC50 317.98 and 328.09 µg/mL for aqueous and ethyl acetate fractions, respectively. But, antioxidant activities for butylated hydroxytoluene (BHT) as a standard antioxidant showed significant results (18.16 µg/mL). Also, it was confirmed that antioxidant activities with the phenolic and flavonoid content of the plant for the aqueous and ethyl acetate elements were obtained 57.73, 59.81 and 21.95, 26.124 µg/mg, respectively. Furthermore, in ß-carotene/linoleic acid assay, inhibition percentages were recorded 71.17 and 96.24 for the aqueous and ethyl acetate elements, respectively. Therefore, ethyl acetate section of the plant showed antioxidant activity more than aqueous part. Hydrogen peroxide scavenging assay evaluated antioxidant activity for aqueous and the ethyl acetate extracts sections as 565 and 560 µg/mL, respectively. Also, power determinations of iron (III) oxide antioxidants from aqueous and ethyl acetate fractions were 6113 and 2.69, respectively. Furthermore, Anti-cancer activity of aqueous and ethyl acetate components evaluated in brine shrimp lethality test with LC50 about 100 and 700 µg/mL for aqueous and ethyl acetate fractions, respectively. The results showed that aqueous section species has a much lower effect than the calculated standard, but ethyl acetate section of the plant sample shows a more favorable effect than the standard. Therefore, the plant screened good antimicrobial, antioxidant and anti-cancer activities for its essential oil and ethyl acetate extract.

Experimental and statistical analysis on a nanostructured sensor for determination of p-hydroxybenzoic acid in cosmetics.

In this research, differential pulse voltammetry (DPV) coupled with experimental design, was used for determination of p-hydroxybenzoic acid (PHB) in cosmetics. Optimization of effecting parameters was carried out based on rotatable central composite design (RCCD) and response surface methodology (RSM) at the surface of a nanostructured electrode for achieving the best sensitivity. Sol-gel process was used for synthesize of nickel titanate (NiTiO3) nanoceramics. The structural and morphological characterization of the nanoparticles was studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Then the NiTiO3 nanopowders were used for surface modification of a carbon paste modified electrode (CPE). Surface characterization of the electrode was accomplished using SEM, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Under the optimized conditions, the voltammograms exhibited two linear dynamic ranges of 0.7-80.0 µM and 80.0-1000.0 µM for PHB with the detection limit of 62.0 nM (S/N = 3). Finally the NiTiO3 nanoceramics modified carbon paste electrode (NiTiO3/CPE) could be employed for the determination of PHB in real samples with satisfactory results.

A carbon paste electrode modified with a nickel titanate nanoceramic for simultaneous voltammetric determination of ortho- and para-hydroxybenzoic acids.

An electrochemical sensor is described for the simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB). The sensor consists of a carbon paste electrode modified with nickel titanate nanoceramics (NiTiO3/CPE). The NiTiO3 nanoceramics and the nanostructured modified CPE were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry. Differential pulse voltammetry indicates that the response to OHB (best measured at 0.90 V vs. Ag/AgCl) and PHB (measured at 0.80 V vs. Ag/AgCl) is significantly improved at the modified CPE compared to a bare CPE. The limits of detection (at S/N = 3) are 0.38 and 0.10 µM for OHB and PHB, respectively. The method was applied to the determination of the two isomers in peeling skin lotion and during the Kolbe-Schmitt reaction. Graphical abstract Nickel titanate nanoceramics (NiTiO3) were synthesized by a sol-gel method. Then, a carbon paste electrode modified with NiTiO3 (NiTiO3/CPE) was constructed. The modified electrode was applied to the interference-free and simultaneous determination of ortho-hydroxybenzoic acid (OHB) and para-hydroxybenzoic acid (PHB).

Three-dimensional Pd/Pt bimetallic nanodendrites on a highly porous copper foam fiber for headspace solid-phase microextraction of BTEX prior to their quantification by GC-FID.

The preparation of bimetallic Pd/Pt nanofoam for use in fiber based solid-phase microextraction (SPME) is described. First, a highly porous copper foam was prepared on the surface of an unbreakable copper wire by an electrochemical method. Then, the substrate was covered with metallic Pd and Pt using galvanic replacement of the Cu nanofoam substrate by applying a mixture of Pd(II) and Pt(IV) ions. The procedure provided an efficient route to modify Pd/Pt nanofoams with large specific surface and low loading with expensive noble metals. The fiber was applied to headspace SPME of benzene, toluene, ethylbenzene and xylene (BTEX) (as the model compounds) in various spiked water and wastewater samples. It was followed by gas chromatography-flame ionization detection (GC-FID). A Plackett-Burman design was performed for screening the experimental factors prior to Box-Behnken design. Compared with the commercial PDMS SPME fiber (100 µm), it had higher extraction efficiency for BTEX. Under the optimum conditions, the method has low limits of detection (0.16-0.35 µg L-1), a wide linear range (1-200 µg L-1), relative standard deviations between 5.8 and 10.5%, and good recoveries (>85% from spiked samples). Graphical abstract Schematic presentation of a three-dimensional Pd/Pt bimetallic nanodendrites supported on a highly porous copper foam fiber for use in headspace solid phase microextraction of BTEX. They were then quantified by gas chromatography-flame ionization detector.

In-situ growth of zeolitic imidazole framework-67 on nanoporous anodized aluminum bar as stir-bar sorptive extraction sorbent for determining caffeine.

The objective of the present study was to develop a simple, sensitive and cost-effective sample pretreatment technique to extract and determine caffeine in different samples of beverage as well as urine. An anodized aluminum bar was electrochemically prepared and employed as nanoporous substrate for in-situ growth of crystals of the zeolitic imidazole framework-67 (ZIF-67). The above-mentioned sorbent, too, was applied as a stir bar sorptive extraction (SBSE) device along with HPLC-UV. Under predetermined experimental condition, the detection limit of the aimed method was 0.05 µg L-1 in beverages, and it was 0.1 µg L-1 in urine samples. Moreover, the linear dynamic range was 0.2-200 µg L-1 for beverages, and it was 0.5-200 µg L-1 for urine samples, too. The inter-day RSDs (10 µg L-1) were 5.3% and 5.7% respectively, and they were 5.8% and 6.1% for intra-day RSDs (10 µg L-1) in beverages and urine samples. Bar to bar reproducibility for three prepared bars equaled 6.2%. The applicability of the SBSE-HPLC-UV was investigated by determining caffeine in different samples of beverage and urine. The final range of obtained spiking recoveries was from 91.2 to104%.

Magnesium-aluminum-layered double hydroxide-graphene oxide composite mixed-matrix membrane for the thin-film microextraction of diclofenac in biological fluids.

Herein, the applicability of Mg-Al-layered double hydroxide-graphene oxide (LDH/GO) mixed-matrix membrane (MMM) for microextraction purposes is reported for the first time. The LDH/GO MMM was used as sorbent for the thin film microextraction (TFME) of diclofenac in human body fluids. The prepared LDH/GO composite has been incorporated into a mechanically stable polyvinylidene difluoride (PVDF) membrane. The contribution of GO in LDH/GO composites significantly improved the extraction efficiency of the TFME sorbent. After elution with methanol, diclofenac was quantified by high performance liquid chromatography-ultraviolet detection (HPLC-UV). Plackett-Burman design was used for screening the experimental factors of interest and specify the significant variables affecting the extraction efficiency. The effective factors were optimized using Box-Behnken design (BBD). Under the optimum conditions, limits of detections (LODs) were 0.14, 0.23 and 0.57 µg L-1 in water, urine and plasma samples, respectively. Limits of quantifications (LOQs) were 0.46, 0.76 and 1.8 µg L-1 in water, urine and plasma samples, respectively. Relative standard deviations (RSDs) at a spiked concentration of 10 µg L-1 were 6.7, 6.9 and 7.1% (as intra-day RSD) in water, urine and plasma samples, respectively. The linear dynamic ranges (LDRs) were in the range of 0.5-200 µg L-1. The applicability of the method was investigated by the extraction and determination of diclofenac in different biological fluids including urine and plasma samples.

Nanoparticle-templated hierarchically porous polymer/zeolitic imidazolate framework as a solid-phase microextraction coatings.

A two-step ZnO nanoparticle-directed method has been implemented to prepare polymer monolith/zeolitic imidazolate framework (ZIF) solid-phase microextraction (SPME) fiber coatings with hierarchical micro-meso-macroporosity. The polymer/ZIF monolith was prepared on the surface of a stainless steel wire from a polymerization mixture containing dispersed ZnO nanoparticles. The embedded ZnO nanoparticles in the precursor polymer monolith coating were converted on-fiber to submicrometric porous crystals of the prototypical ZIF-8, based on the coordination of Zn(II) with 2-methylimidazole. The polymer/ZIF monolith coating was applied to the headspace SPME of benzene, toluene, ethylbenzene, and xylenes (BTEX) from water samples, followed by gas chromatography-flame ionization detection (GC-FID). Hierarchically porous polymer/ZIF monolithic coatings showed a superior performance for BTEX extraction in comparison to coatings based on pure macroporous organic polymer monoliths, silicone glue/ZIF-8 coatings or commercial PDMS coatings. Experimental parameters such as desorption temperature, desorption time, salt concentration, temperature effect, equilibrium time and extraction time were investigated. Under the selected experimental conditions, limits of detection of 0.02-0.11 µg L-1, linear ranges of 0.2-200 µg L-1, relative standard deviations of 4.3-8.2%, and a fiber-to-fiber reproducibility of 8.9-9.8% (n = 3) were obtained. Recoveries higher than 88% were obtained for BTEX analysis in tap water, wastewater and landfill leachates.

Combination of GC/FID/Mass spectrometry fingerprints and multivariate calibration techniques for recognition of antimicrobial constituents of Myrtus communis L. essential oil.

Myrtus communis L. is an aromatic evergreen shrub and its essential oil possesses known powerful antimicrobial activity. However, the contribution of each component of the plant essential oil in observed antimicrobial ability is unclear. In this study, chemical components of the essential oil samples of the plant were identified qualitatively and quantitatively using GC/FID/Mass spectrometry system, antimicrobial activity of these samples against three microbial strains were evaluated and, these two set of data were correlated using chemometrics methods. Three chemometric methods including principal component regression (PCR), partial least squares (PLS) and orthogonal projections to latent structures (OPLS) were applied for the study. These methods showed similar results, but, OPLS was selected as preferred method due to its predictive and interpretational ability, facility, repeatability and low time-consuming. The results showed that α-pinene, 1,8 cineole, ß-pinene and limonene are the highest contributors in antimicrobial properties of M. communis essential oil. Other researches have reported high antimicrobial activities for the plant essential oils rich in these compounds confirming our findings.

Preparation of a manganese titanate nanosensor: Application in electrochemical studies of captopril in the presence of para-aminobenzoic acid.

This study reports the synthesis and characterization of a novel nanostructure-based electrode for electrochemical studies and determination of captopril (CP). At first manganese titanate nanoceramics were synthesized by the sol-gel method. The structural evaluations of the pure nanopowders were investigated by different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Then it was used to prepare a new nanostructured manganese titanate carbon paste electrode (MnTiO3/CPE). The characterization of the modified sensor was carried out by comprehensive techniques such as electrochemical impedance spectroscopy (EIS), SEM, and voltammetry. Subsequently, the modified electrode was used for CP catalytic oxidation in the presence of para-aminobenzoic acid (PABA) as a mediator. The results showed that PABA has high catalytic activity for CP oxidation. The electrochemical behavior of CP was studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CHA), and differential pulse voltammetry (DPV) techniques. Under the optimized conditions, the catalytic oxidation peak current of CP showed two linear dynamic concentration ranges of 1.0 × 10(-8) to 1.0 × 10(-7) and 1.0 × 10(-7) to 1.0 × 10(-6), with a detection limit of 1.6 nM (signal/noise = 3), using the DPV technique. Finally, the proposed method was successfully applied for determination of CP in pharmaceutical and biological samples.

Improvement of interaction between PVA and chitosan via magnetite nanoparticles for drug delivery application.

Magnetite nanoparticles were synthesized by coprecipitation under ultrasonication followed by coating with chitosan. Polyvinyl alcohol (PVA) is then combined with the chitosan that coated the magnetite nanoparticles. The combination occurs by hydrogen binding and ionic cross-linking of the amino and hydroxyl groups of chitosan and PVA respectively. The magnetite nanoparticles have an average size of 10.62 nm that was confirmed by TEM. The VSM measurements showed that nanoparticles were superparamagnetic. The coatings on the core nanoparticles were estimated by AAS and the attachments of coating to the nanoparticles were confirmed by FT-IR analysis. Physicochemical properties of nanoparticles were measured by DLS and zeta potential. Naked magnetite, chitosan and PVA coating have zeta potential of +36.4, +48.1 and -12.5 mV respectively. The unspecific adsorption and interaction between nanoparticles and bovine serum albumin (BSA) were investigated systematically by UV-vis spectroscopy method. The nanoparticles that were modified by PVA present low protein adsorption, which makes them a practical choice for preventing opsonization in clinical application and drug delivery.

Design and evaluation of a highly sensitive nanostructure-based surface modification of glassy carbon electrode for electrochemical studies of hydroxychloroquine in the presence of acetaminophen.

N,N'-bis[(E)-(1-pyridyl) methylidene]-1,3-propanediamine (PMPDA) self-assembled monolayer (SAM) was covalently prepared on a glassy carbon electrode (GCE). The electrode surface modification was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Then GC-PMPDA SAM modified electrode was used to investigate the electrochemical behavior of hydroxychloroquine (HQ) using CV, double potential step chronocoulometry and linear sweep voltammetry (LSV) techniques. Using these techniques, the diffusion coefficient (D), electron transfer coefficient (α) and exchanging current density (j0) for HQ were calculated. Furthermore the modified electrode was applied as a high sensitive biosensor for determination of HQ in the presence of acetaminophen (AC). The GC-PMPDA SAM modified electrode provides two linear responses for HQ in the presence of AC in the concentration ranges from 0.09 to 10.21 µM and 10.21 to 98.29 µM by differential pulse voltammetry (DPV). The detection limit (three times the signal blank/slope) was 4.65 nM. Finally the modified electrode was satisfactorily used for determining of HQ in human body fluids.

Three-dimensional voltammetry: a chemometrical analysis of electrochemical data for determination of dopamine in the presence of unexpected interference by a biosensor based on gold nanoparticles.

Multivariate curve resolution by alternating least-squares (MCR-ALS) was used for voltammetric determination of dopamine (DA) in the presence of epinephrine (EP) at a gold nanoparticles chemically modified carbon paste electrode (AuNPs/CPE). Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques were applied for characterization of the nanostructure modified electrode. Central composite rotatable design (CCRD) was employed to generate an experimental program to offer data to model the effects of different parameters on voltammetric responses. Response surface methodology (RSM) was applied to show the individual and interactive effects of chemical and instrumental variables at five levels, combined according to CCRD. For determination of DA in the presence of unexpected interference, three-way data were achieved from various pulse heights in differential pulse voltammetry (DPV) technique. This type of data construction, analyzed by MCR-ALS, makes it possible to exploit the so-called "second-order advantage". The second-order advantage provided unbiased results even in the presence of electroactive interferences with highly overlapped peaks. Also, an algorithm was applied to correct the detected potential shift in the voltammetric data. The voltammograms of the samples were then deposited in an augmented data matrix (column-wise) and subsequently analyzed by MCR-ALS. The effect of rotational ambiguity associated with a particular MCR-ALS solution under a set of constraints was also studied. The proposed method could be applied for the determination of DA and EP in the presence of each other in a wide concentration range of 0.1-205.0 µM, and the detection limit of DA has been found to be 35.5 nM. Finally, the technique has been used for the reliable analysis of DA in real samples.

Sensitive and selective determination of hydroxychloroquine in the presence of uric acid using a new nanostructure self-assembled monolayer modified electrode: optimization by multivariate data analysis.

A highly sensitive electrochemical nanosensor was developed using covalent modification of a glassy carbon electrode (GCE) by self-assembly of a novel Schiff base. Scanning electron microscopy (SEM) and electrochemical techniques were used to investigate the immobilization of the self-assembled monolayer (SAM) on the GCE. The electrochemical behavior of hydroxychloroquine (HCQ) in the presence of uric acid (UA) at the surface of the modified electrode was studied using the differential pulse voltammetry (DPV) technique. Response surface methodology (RSM) is used to optimize the effects of various operating variables such as pH, immersion time, scan rate, step potential and modulation amplitude on the voltammetric response of HCQ. RSM formulates a mathematical model which correlates the independent parameters with the peak current of HCQ. The central composite rotatable design (CCRD) has been applied to conduct the experiments. Then, under the optimized conditions, HCQ was determined in the presence of UA. The electrochemical measurements demonstrated that this biosensor responded well to HCQ, confirming that the self-assembly immobilization method was effective. Also, the interference, the storage stability, and the reproducibility of the biosensor were studied and assessed. The developed nanosensor was economical and efficient, making it potentially attractive for application to real sample analysis.

Multivariate curve resolution-alternating least squares assisted by voltammetry for simultaneous determination of betaxolol and atenolol using carbon nanotube paste electrode.

In the present work differential pulse voltammetry coupled with multivariate curve resolution-alternating least squares (MCR-ALS) was applied for simultaneous determination of betaxolol (Bet) and atenolol (Ate) in 0.20 M Britton-Robinson (B-R) buffer solution at the surface of a multi-walled carbon nanotube modified carbon paste electrode (MWCNT/CPE). Characterization of the modified electrode was carried out by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). A strategy based on experimental design was followed. Operating conditions were improved with central composite rotatable design (CCRD) and response surface methodology (RSM), involving several chemical and instrumental parameters. Then second order data were built from variable pulse heights of DPV and after correction in potential shift analyzed by MCR-ALS. Analytical parameters such as linearity, repeatability, and stability were also investigated and a detection limit (DL) of 0.19 and 0.29 µM for Bet and Ate was achieved, respectively. The proposed method was successfully applied in simultaneous determining the two analytes in human plasma.

A new method for the simultaneous analysis of strychnine and brucine in Strychnos nux-vomica unprocessed and processed seeds using a carbon-paste electrode modified with multi-walled carbon nanotubes.

INTRODUCTION: Strychnos nux-vomica L. (Loganiaceae), widely used in folk medicine, is grown extensively in southern Asian countries. Its major bioactive constituents are strychnine and brucine, which are frequently used in traditional herbal medicines for treatment of nervous diseases, vomiting and traumatic pain. OBJECTIVE: A new method using a carbon-paste electrode modified with multi-walled carbon nanotubes (CNT/CPE) was developed and validated for single or simultaneous determination of strychnine and brucine in Strychnos nux-vomica seeds. Additionally, an environmentally friendly method was successfully applied to reduce the levels of strychnine and brucine in seeds. MATERIALS AND METHODS: Cyclic voltammetry, chronocoulometry and differential pulse voltammetry were used with multi-walled carbon nanotube modified carbon-paste electrodes. RESULTS: The peak currents increase linearly with the strychnine and brucine concentrations in the ranges of 50-1000 and 5-355 µ m, and the detection limits for strychnine and brucine were 0.43 and 0.28 µ m, respectively. Of the processing methods used, the greatest reduction in the strychnine and brucine levels was observed in samples processed using milk and saltwater. CONCLUSION: A new, sensitive and selective method was developed for the measurement of strychnine and brucine. This method was successfully applied to the determination of strychnine and brucine in unprocessed and processed Strychnos nux-vomica seed.