Britton-Robinson Buffer Solution Research Articles

Simultaneous determination of hydrochlorothiazide and valsartan in combined dosage forms: Electroanalytical performance of cathodically pretreated boron-doped diamond electrode

This work deals with simultaneous determination of hydrochlorothiazide (HCTZ) and valsartan (VAL) by square-wave voltammetry using a cathodically pretreated boron-doped diamond electrode. The method exhibits linear responses to HCTZ and VAL in the concentration range 1.97–88.1μmolL−1 and 9.88–220μmolL−1, respectively, in a Britton–Robinson buffer solution (pH 5.0), with detection limits of 0.639μmolL−1 and 0.935μmolL−1, respectively. The proposed method was successfully applied in the simultaneous determination of both antihypertensives in combined dosage forms and the results are in close agreement with those obtained using high performance liquid chromatography method.

Flow-injection amperometric determination of yohimbine alkaloid in dietary supplements using a boron-doped diamond electrode

A simple, rapid and sensitive flow-injection method for the amperometric determination of the alkaloid yohimbine using a boron-doped diamond electrode has been developed. Best conditions for flow-injection analysis were a detection potential of +1.20V (vs. Ag/AgCl) and a flow rate of 1.4mLmin−1 with an injection volume of 100μL in Britton–Robinson buffer solution at pH 7 as a carrier. The current response of yohimbine was proportional in the concentration range from 0.3 to 100μM with two linear segments (0.3–10 and 10–100μM) and a low detection limit of 0.15μM (0.053mgL−1) as well as good repeatability (relative standard deviation of 4.5% for n=10) were achieved. The sampling frequency was calculated about 70 injectionsh−1. The practical analytical usefulness of the developed procedure was successfully demonstrated in the determination of yohimbine in dietary supplements with good recoveries (94–98% and 92–95%) for Pausinystalia yohimbe and Rauvolfia serpentina, respectively.

New contribution in the study of phase formation in mixed alkanethiol self-assembled monolayers: a powerful tool for transducers design

Here, the formation of distinct 3-mercaptopropionic acid (MPA) and 11-mercaptoundecanoic acid (MUA) domains on polycrystalline gold surfaces was investigated by cyclic voltammetry and electrochemical quartz crystal nanobalance. Voltammetric experiments with the [Fe(CN)6]4-/3− redox couple showed that the MPA SAM allowed electron transference at the same rate as the bare gold surface, while the MUA SAM blocked the entire electrode surface. The chemical nature of mixed SAMs is discussed by evaluating the mass variations and the respective molecular weight in the desorption potential regions for each thiol by electrochemical quartz crystal nanobalance. Different domains containing MUA, MPA and their mixtures were identified in the massograms, thus demonstrating MPA island domains and the electrochemical response obtained for the [Fe(CN)6]4-/3− redox couple. The modified surfaces, as well as bare Au electrode, were used for electroanalysis of the flavonoid fisetin in Britton-Robinson buffer solution, pH 5. Depending on the modification, detection limits as low as 3.35 ×10−10molL−1, which attests the possibility of use such surfaces in electroanalysis.

Correlation between Electrocatalytic Oxygen Reduction Reaction and Structure of Mononuclear CuII Complex at Various pH

Introduction Cathode catalysts without using platinum have been extensively investigated over the past several decades for the significance of cost reduction of polymer electrolyte fuel cell.Metallocomplexes is one of prospective non-Pt-based cathode catalysts such as metalloporphyrin and metallophthalocyanin. Bisides these complexes, Cu complexes supported by pyridylalkylamine ligands have recently attracted increasing attention as alternative oxygen reduction catalysts, which are known as a model of some dioxygen-activating enzymes. The Cu complex has the potential to have good oxygen reduction reaction (ORR) activity because some original enzymes such as cytochrome c oxidase (CcO) catalyze oxygen reduction with high efficiency. Although, some studies of the ORR activity of the Cu complexes on an immobilized electrode in an aqueous solution have been reported recently1), the correlation between the ORR activity and the redox property of the CuII/CuI couple of the complex has been unclear. Therefore, it is very important to analyze the relationship between the ORR activity and the redox properties of CuII/CuI of the Cu complexes for the improvement of the ORR performance. In this study, we examined the redox properties of a copper complex, CuII-tmpa [tmpa = tris(2-pyridylmethyl)amine] in a buffer solution at various pH, and investigated its effect on the ORR activity. Experiments The CuII complexes supported by tmpa were synthesized according to the reported procedures2). Voltammograms under quiescent conditions were taken in 10 mM Britton-Robinson buffer solution (CH3COOH, H3PO4, H3BO3, supporting electrolyte: 10 mM Na2SO4) containing 0.3 mM of the copper complex. All measurements in this study were performed using glassy carbon as a working electrode, Pt coil as a counter electrode, and Ag|AgCl|KCl(sat.) as a reference electrode. Results and discussion Figure 1 shows voltammograms of CuII–tmpa under quiescent and oxygen-saturated conditions. The data was displayed versus RHE. The voltammograms show that CuII–tmpa has the ORR activity in a wide range of pH and decreases in overpotential as pH was raised, though the current density was decreased above pH 12.0.CuII–tmpa under argon-saturated conditions showed clear reversible voltammograms of CuII/CuI redox pair, so that we were able to evaluate the redox potential. A potential-pH diagram reveals that a pKa value of CuI species is ca. 12.0. This result suggests that hydroxyl anion coordinates the CuI center in the strong alkaline solution, which causes the catalytic current decrease. We will also discuss about additional results of spectroscopic measurement which support the hypothesis as shown above with respect to the structure of CuII–tmpa. References 1) M. A. Thorseth, C. S. Letko, E. C. M. Tse, T. B. Rauchfuss, A. A, Gewirth, Inorg. Chem. 2013, 52, 6282) Z. Tyeklar, R. R. Jacobson, N. Wei, N. N. Murthy, J. Zubieta, K. D. Karlin, J. Am. Chem. Soc., 1993, 115, 2677

Sensitive detection of sulfasalazine at screen printed carbon electrode modified with functionalized multiwalled carbon nanotubes

A new home-made screen-printed carbon electrode (SPCE) modified with a functionalized multiwalled carbon nanotubes (MWCNTCOOH) and benzyl acetate (BA) was prepared for electrochemical determination of sulfasalazine (SSZ). Determination of SSZ was carried out by differential pulse voltammetry (DPV) in 0.04molL−1 Britton-Robinson buffer solution of pH 1.7 at −40mV (versus Ag/AgCl) at MWCNTCOOH/BA-SPCE. The electrochemical behavior of the modified SPCEs was investigated by cyclic voltammetry and impedance spectroscopy. The effects of various parameters on the response of the electrode such as type of modifier, pH of the buffer, and DPV parameters were investigated. The reduction peak current obtained from DPV of SSZ increased linearly with its concentration at the ranges of 1.0–14μmolL−1 and 14–70μmolL−1 with sensitivities of 1.84 and 0.48μAμM−1cm−2. The relative standard deviation (RSD%) of seven replicates of current measurements for a 20μmolL−1 of SSZ solution was 3.2%. The detection limit of the method was found to be 0.3μmolL−1. The prepared sensor was successfully applied for the determination of SSZ in pharmaceutical formulation and biological fluid samples.

Gold nanoparticles-based localized surface plasmon resonance scattering analysis method for the determination of trace amounts of Hg(II)

Heavy-metal ions pose severe risks for human health and the environment. In particular, mercury-based pollutants are of great environmental concern because of the high toxicity of many Hg compounds. It is important to monitor the levels of potentially toxic metal Hg(II) in aquatic ecosystems. Gold nanoparticles (AuNPs) as nanomaterials have been generally studied. It is because their unique electrical, chemical, optical, and catalytic properties, AuNPs have caused widespread interest for applications in biological and chemical analysis and detection. In the present work, the authors took advantage of the aggregation-induced localized surface plasmon resonance (LSPR) light scattering signal change of sodium thioglycolate functionalized AuNPs in aqueous solutions to develop a highly efficient optical sensor for Hg(II). The as-modified AuNPs demonstrate that high negative charge densities exist on their surfaces at pH 9.0 Britton-Robinson (BR) buffer solution. The AuNPs occur aggregate in solution through chelation in the presence of Hg(II). The scanning electron microscope (SEM) images for the AuNPs display typical shapes of these AuNPs as regular and almost individual spherical particles. The color change of the AuNPs solution was induced by the addition of Hg(II) and it immediately changed from red to purple due to the aggregation. Under optimum conditions, a good linear relationship was obtained from 0.08 to 0.8 μmol x L(-1) with a correlation coefficient of 0.997 6, and the limit of detection (LOD) was 8.0 nmol x L(-1). PEG20000 was employed as a system stabilizer. The proposed method has an excellent selectivity for Hg(II) in aqueous medium over other metal ions. The optimum test of reaction conditions, including the amount of AuNPs, pH value, reaction stability and ionic strength, were also investigated. This method has been used for determination of Hg(II) successfully in environmental water sample. This approach manifested several advantages including short analysis time, high sensitivity, low cost, excellent selectivity and ease of operation.

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO2 nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO2 coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM−1, while for epinephrine these values are ~60 nM and 0.19 μA μM−1. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Stripping voltammetric determination of manganese in bioethanol

In this work, we describe the first electroanalytical method for manganese (Mn (II) determination in bioethanol based on square-wave cathodic stripping voltammetry (SWCSV) at a bare glassy-carbon electrode. Bioethanol is directly diluted in a Britton–Robinson buffer solution (pH4.0) and a stripping peak for Mn(II) is attained at approximately 0.9V (vs. Ag/AgCl). After optimizing SWCSV parameters (deposition potential and time, stirring speed, amplitude, frequency and step potential), the proposed method presented low relative standard deviation between injections (5.6%, n=10), low detection limit (16μgL−1) for a 300s deposition time and 40-fold dilution, a linear range between 3 and 175μgL−1, and adequate recovery values (90–110%) in fortified samples.

Ionic silsesquioxane film immobilized on silica applied in the development of carbon paste electrode for determination of methyl parathion

A mesoporous silica-based hybrid material composed of silica xerogel modified with an ionic silsesquioxane, which contains the 1,4-diazoniabicyclo[2.2.2]octane chloride group, was obtained. The silsesquioxane film is highly dispersed on the surface. This hybrid material was utilized to develop a carbon paste electrode (CPE) for determination of methyl parathion. Transmission FTIR, elemental analysis and N2 adsorption–desorption isotherms were used for characterization of the material. The electrochemical behavior of methyl parathion was evaluated by cyclic voltammetry and differential pulse voltammetry. It was observed a linear response to methyl parathion in the concentration range from 1.25 × 10−7 to 2.56 × 10−6 mol L−1 by employing the carbon paste electrode, in Britton–Robinson buffer solution (pH 6). The achieved detection limit (3 SD of the blank divided by the slope of calibration curve) was 0.013 µmol L−1 and sensitivity was 6.3 µA µmol L−1. This result shows the potentiality of this electrode for application as electrochemical sensor for methyl parathion.

Voltammetric behavior of doxorubicin at a renewable silver-amalgam film electrode and its determination in human urine

Voltammetric characterization of doxorubicin (DOX) and its determination using a renewable silver-amalgam film electrode (Hg(Ag)FE) was performed by direct cathodic square-wave voltammetry (SWV) and by the highly sensitive adsorptive square-wave voltammetry (AdSWV) in aqueous Britton-Robinson buffer solutions as supporting electrolyte (pH 2.0-8.0). The Hg(Ag)FE response of DOX was monitored in the potential range between -0.20 and -0.80V. For the trace level analysis the method optimization showed that the optimal conditions were: the pH 6.0, the accumulation potential -0.20V, and the accumulation time 140 s. In the model solutions, DOX was determined in the concentration range of 4.99-59.64ngmL−1. The developed AdSWV method was applied for the determination of DOX in spiked human urine sample. The lowest concentration of DOX of 9.89ngmL−1 was determined with the relative standard deviation less than 6%.

Application of multivariate curve resolution alternating least squares to biomedical analysis using electrochemical techniques at a nanostructure-based modified sensor

Application of multivariate curve resolution alternating least squares (MCR-ALS), for the resolution and quantification of two sulfonamide drugs containing sulfamethizole (SMT) and sulfapyridine (SPY) with a very high degree of overlapping voltammograms, is described. A simple and sensitive carbon nanocomposite electrode has been developed for the electrochemical trace determination of SMT and SPY in Britton-Robinson (B-R) buffer solution. This sensor was designed by incorporation of multi-walled carbon nanotubes (MWCNTs) into the carbon paste electrode (CPE). Response surface methodology (RSM) using central composite rotatable design (CCRD) model was used to optimize effective parameters on differential pulse voltammetry (DPV) response of the two analytes. A 4-factor-5-level CCRD of RSM was applied to model linear, interaction and quadratic effects of chemical and instrumental variables. After potential shift correction, MCR-ALS has been applied to data collected from DPV analysis of the oxidation process of SMT and SPY in different pulse heights. Quantitative voltammetric analyses of SMT and SPY were performed in the concentration range of 0.1-180.0 and 0.5-165.0μM, and it was found that the detection limits were 50.0 and 60.0nM, respectively. The method was applied for simultaneous determination of SMT and SPY in spiked human serum and urine samples.

Sensitive Voltammetric Determination of Niclosamide at a disposable pencil graphite electrode

Niclosamide (NA), an effective drug against tapeworm infections, was electrochemically studied using a pencil graphite electrode (PGE). A low-cost sensitive and selective procedure was developed for determination of NA by recording differential pulse voltammograms of NA in pH 7.0 Britton-Robinson buffer solution containing 0.1M KCl and 30% DMF at the PGE. The PGE displayed very good electrochemical behavior with significant enhancement of the peak current compared to a glassy carbon electrode. Moreover, results obtained from the differential pulse voltammograms show that PGE offers a disposable, low cost, selective and sensitive electrochemical sensor for determination of NA. Under experimental conditions, the PGE had a linear response range from 0.05μM to 10μM NA with a detection limit of 0.015μM (based on 3sb). A relative standard deviation of 0.57% was obtained for five successive determinations of 5μM NA, which indicate acceptable repeatability. This voltammetric method was successfully applied to the direct determination of NA in tablets. No interference from the tablet excipients was encountered.

Electrochemical Oxidation of the Fungicide Dimoxystrobin and Its Amperometric Determination by Batch-Injection Analysis

The electrochemical oxidation of dimoxystrobin at a boron-doped diamond electrode is reported. Two well-defined oxidation peaks were observed at around 1350 and 1750 mV in a 0.04 mol L−1 Britton-Robinson buffer solution (pH 10). Based on this electrochemical process, a batch-injection analysis method with amperometric detection was developed for the determination of dimoxystrobin in natural waters. The method presented a high analytical frequency (180 h−1), good precision (RSD < 3%, n = 10), and a detection limit of 0.38 µmol L−1 (124 ng mL−1). Recovery values obtained using analyte fortified water samples were between 80 and 105%. Additionally, a simple strategy to detect the presence of interfering molecules in water samples based on dual-pulse amperometry is presented.

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

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

Voltammetric determination of 2-amino-6-nitrobenzothiazole and 5-nitrobenzimidazole using a silver solid amalgam electrode modified by a microcrystalline natural graphite–polystyrene composite film

Voltammetric behavior of two genotoxic nitro compounds (2-amino-6-nitrobenzothiazole, ANBT, and 5-nitrobenzimidazole, 5-NBIA) has been investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a polished silver solid amalgam electrode modified by microcrystalline natural graphite–polystyrene composite transducer (shortly denoted as carbon film electrode – CFE). The optimum conditions have been found for their determination in the Britton–Robinson buffer solutions. The practical applicability of the newly developed methods was verified on model samples of drinking and river waters.

Development of electrochemical sensor based on β-cyclodextrin/K10 montmorillonite towards the enhanced electro-catalytic oxidation of isoorientin: A voltammetric study

Abstract The electrochemical oxidation and interfacial electron transfer behavior of isoorientin at carbon paste electrode (CPE) and carbon paste electrode modified with β-cyclodextrin/K 10 Montmorillonite (β-CD/K 10 Mt/MCPE) have been studied by employing cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The modified electrode showed excellent electrocatalytic activity towards the determination of isoorientin oxidation in 0.1 M Britton-Robinson (BR) buffer solution of pH 3.0. The electrochemical process was found to be reversible and adsorption controlled. The experimental parameters which influence the determination of isoorientin such as effect of pH, scan rate, concentration, accumulation time, stability and repeatability have been optimized. The peak currents were found to be linear in the range of 2.5 × 10 −7 to 2.5 × 10 −5 M with the detection limit of 2.95 × 10 −7 M, quantification limit of 9.86 × 10 −7 M and correlation co-efficient of 0.9994, respectively. The effect of interference was also studied by employing DPV.

Electrochemical behavior of methamphetamine and its voltammetric determination in biological samples using self-assembled boron-doped diamond electrode

An electrochemical behavior of methamphetamine on a self-assembled boron-doped diamond electrode was studied by cyclic voltammetry. Methamphetamine yielded a single irreversible oxidation peak at a higher positive potential of +1.23V (vs. Ag/AgCl/3M KCl electrode) in Britton-Robinson buffer solution at pH 10. The nature of the electrode reaction was found to be diffusion controlled with minor contribution of adsorption. The differential pulse voltammetric methodology was proposed for the sensitive determination of methamphetamine in a linear concentration range from 0.07 to 80μM with a detection limit of 0.05μM (7.46μgL−1) and a good repeatability (relative standard deviation of 2.8% at 20μM concentration level, n=6). The effect of interfering agents (common urinary compounds) was appeared to be negligible confirming a favorable selectivity of method. The practical usefulness of method was demonstrated in the assessment of methamphetamine content in model human urine samples with good accuracy (recoveries varied from 93.4% to 97.6%). The proposed procedure could represent a suitable alternative to other analytical methods for the determination of low concentration levels of methamphetamine in biological samples. It may enable methamphetamine excreted in urine of drug addicted people to be assayed sensitively and selectively.

STABILITY-INDICATING HPLC METHOD FOR SIMULTANEOUS DETERMINATION OF CAPTOPRIL, INDAPAMIDE, AND THEIR RELATED COMPOUNDS

A validated stability-indicating HPLC method was developed for simultaneous determination of Captopril (CP), Indapamide (ID), and their related compounds in tablets using a 250 × 4.6 mm Xterra RP8 column, 5 µm particle size with UV detection at 210 nm. Isocratic elution was employed using mobile phase consisting of a mixture of 26 mM pentane-1-sulfonic acid sodium salt in 30 mM potassium dihydrogen phosphate (pH 2.8, adjusted by phosphoric acid):methanol:acetonitril (6:2:2) v/v/v. The described method was linear over the range of 0.25–150 µg/mL with (r = 0.9999) for CP and 0.2–100 µg/mL with (r = 0.9999) for ID. The stability of CP and ID was studied under accelerated acidic, alkaline, and oxidative conditions. The proposed method was used to investigate the kinetics of acidic and alkaline degradation process of CP and ID at different temperatures and the apparent pseudo first-order rate constant, half-life, and activation energy were calculated. The pH rate profiles of degradation of CP and ID in Britton-Robinson buffer solutions within the pH range 1.8–12.0 were studied. The developed method was validated with respect to linearity, accuracy, precision, selectivity, and robustness. The forced degradation studies prove the stability indicating power of the developed method.

Modification-free electrochemical approach for sensitive monitoring of purine DNA bases: Simultaneous determination of guanine and adenine in biological samples using boron-doped diamond electrode

A simple and modification-free electrochemical sensor for sensitive determination of purine DNA bases based on the use of bare and electrochemically un-pretreated boron-doped diamond electrodes is proposed. Cyclic voltammetry showed that guanine and adenine provided well defined irreversible oxidation peaks at +1.15 and +1.35V vs. Ag/AgCl/3M KCl, respectively, in Britton–Robinson buffer solution at pH 6 with sufficient potential separation. Both analytes provided a linear relation between peak current and concentration in the range from 0.3 to 19μM when both were present in the solution. For individual analytes in the absence of the other, the corresponding ranges for guanine and adenine were from 0.21 to 23μM and from 0.12 to 25μM, respectively. The limits of detection for guanine and adenine were 158 and 67nM, respectively, for simultaneous determinations in differential pulse mode, and 37 and 19nM, respectively, for individual quantifications. The proposed method was successfully applied for the assessment of guanine and adenine content in spiked human urine samples with satisfactory results. The analysis of native, thermally and acid denatured DNA samples from fish sperm and acid denatured DNA samples from human placenta yielded two oxidation peaks corresponding to guanine and adenine residues with (G+C)/(A+T) values close to those reported in literature. In this way, boron-doped diamond represents a modification-free electrochemical alternative to widely used modified electrodes for sensitive monitoring of purine DNA bases.

Electrochemical characterization of luminol and its determination in real samples

The electrochemical behavior of luminol, an important molecule in forensic science, was studied in Britton–Robinson buffer solution (pH 2–pH 13) at a glassy carbon electrode using cyclic voltammetry and differential pulse voltammetry techniques.