Zeolite A functionalized with copper nanoparticles and graphene oxide for simultaneous electrochemical determination of dopamine and ascorbic acid

A novel Cu-zeolite A/graphene modified glassy carbon electrode for the simultaneous electrochemical determination of dopamine (DA) and ascorbic acid (AA) has been described. The Cu-zeolite A/graphene composites were prepared using Cu²⁺ functionalized zeolite A and graphene oxide as the precursor, and subsequently reduced by chemical agents. The composites were characterized by X-ray diffraction, Fourier transform infrared spectra and scanning electron microscopy. Based on the Cu-zeolite A/graphene-modified electrode, the potential difference between the oxidation peaks of DA and AA was over 200 mV, which was adequate for the simultaneous electrochemical determination of DA and AA. Also the proposed Cu-zeolite/graphene-modified electrode showed higher electrocatalytic performance than zeolite/graphene electrode or graphene-modified electrode. The electrocatalytic oxidation currents of DA and AA were linearly related to the corresponding concentration in the range of 1.0 × 10⁻⁷–1.9 × 10⁻⁵ M for DA and 2.0 × 10⁻⁵–2.0 × 10⁻⁴ M for AA. Detection limits (<!-- no-mfc -->S/N<!-- /no-mfc --> = 3) were estimated to be 4.1 × 10⁻⁸ M for DA and 1.1 × 10⁻⁵ M for AA, respectively.     

Construction of a new Cu2+ coated wire ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylidene amino)phenyl)disufanyl)phenylimino)methyl)-4-methoxyphenol Schiff base

In this article a new coated platinum Cu²⁺ ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylideneamino)phenyl)disufanyl)phenylimino) methyl)-4-methoxyphenol Schiff base (L₁) as a new ionophore is described. This sensor has a wide linear range of concentration (1.2 × 10⁻⁷-1.0 × 10⁻¹ mol L⁻¹) and a low detection limit of 9.8 × 10⁻⁸ mol L⁻¹of Cu(NO₃)₂. It has a Nernstian response with slope of 29.54 ± 1.62 mV decade⁻¹ and it is applicable in the pH range of 4.0-6.0 without any divergence in potentioal. The coated electrode has a short response time of approximately 9 s and is stable at least for 3.5 months. The electrode shows a good selectivity for Cu²⁺ ion toward a wide variety of metal ions. The proposed sensor was successfully applied for the determination of Cu²⁺ ion in different real and environmental samples and as indicator electrode for potentiometric titration of Cu²⁺ ion with EDTA.     

Sensitive voltammetric determination of baicalein at DNA Langmuir-Blodgett film modified glassy carbon electrode

The present paper describes to modify a double stranded DNA-octadecylamine (ODA) Langmuir-Blodgett film on a glassy carbon electrode (GCE) surface to develop a voltammetric sensor for the detection of trace amounts of baicalein. The electrode was characterized by atomic force microscopy (AFM) and cyclic voltammetry (CV). Electrochemical behaviour of baicalein at the modified electrode had been investigated in pH 2.87 Britton-Robinson buffer solutions by CV and square wave voltammetry (SWV). Compared with bare GCE, the electrode presented an electrocatalytic redox for baicalein. Under the optimum conditions, the modified electrode showed a linear voltammetric response for the baicalein within a concentration range of 1.0 × 10⁻⁸-2.0 × 10⁻⁶ mol L⁻¹, and a value of 6.0 × 10⁻⁹ mol L⁻¹ was calculated for the detection limit. And the modified electrode exhibited an excellent immunity from epinephrine, dopamine, glucose and ascorbic acid interference. The method was also applied successfully to detect baicalein in the medicinal tablets and spiked human blood serum samples with satisfactory results.     

A novel poly(cyanocobalamin) modified glassy carbon electrode as electrochemical sensor for voltammetric determination of peroxynitrite

This report described the direct voltammetric detection of peroxynitrite (ONOO⁻) at a novel cyanocobalamin modified glassy carbon electrode prepared by electropolymeriation method. The electrochemical behaviors of peroxynitrite at the modified electrode were studied by cyclic voltammetry. The results showed that this new electrochemical sensor exhibited an excellent electrocatalytic activity to oxidation of peroxynitrite. The mechanism of catalysis was discussed. Based on electrocatalytic oxidation of peroxynitrite at the poly(cyanocobalamin) modified electrode, peroxynitrite was sensitively detected by differential pulse voltammetry. Under optimum conditions, the anodic peak current was linear to concentration of peroxynitrite in the range of 2.0 × 10⁻⁶ to 3.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁷ mol L⁻¹ (S/N of 3). The proposed method has been applied to determination of peroxynitrite in human serum with satisfactory results. This poly(cyanocobalamin) modified electrode showed high selectivity and sensitivity to peroxynitrite determination, which could be used in quantitative detection of peroxynitrite in vivo and in vitro.     

Enhanced sensing of ascorbic acid, dopamine and serotonin at solid carbon paste electrode with a nonionic polymer film

A nonionic poly(2-amino-5-mercapto-thiadiazole) film was electrodeposited on a solid carbon paste electrode via a potential scanning procedure, and used for amperometric sensing of ascorbic acid (AA), dopamine (DA) and serotonin (ST). The highly electrocatalytic activity of the sensor to the three analytes was demonstrated from the sensitive and well separated voltammetric signals. The polymer film did not show significant accumulation effect on all the three species, reducing the fouling and deactivation of the electrode surface as well as the mutual interference among the analytes. The sensor achieved amperometric sensitivities of 1.92 nA (nmol L⁻¹)⁻¹ cm⁻² to AA in the linear range of 0.025-1.95 μmol L⁻¹, 3.76 nA (nmol L⁻¹)⁻¹ cm⁻² to DA and 7.00 nA (nmol L⁻¹)⁻¹ cm⁻² to ST both in the linear range of 0.02-1.56 μmol L⁻¹. The lowest detection limits were found to be 1.5, 0.7 and 0.4 nmol L⁻¹ for AA, DA and ST, respectively. This sensor was successfully employed for the successive determination of AA, DA and ST in pharmaceutical samples. The good antifouling property and reproducibility of the proposed sensor can be attributed to the nonionic polymer film without electrostatic attraction to the ionized species in the solutions.     

Voltammetric behavior of copper(I)oxide modified carbon paste electrode in the presence of cysteine and ascorbic acid

The electrochemical behavior of a copper(I)oxide (Cu₂O) modified carbon paste electrode (MCPE) was investigated in different buffer solutions and in the presence of ascorbic acid (AA) and cysteine (RS). Working conditions such as pH, mineral oil, and modifier ratio were optimized. Voltammetric results revealed that RS forms rather stable complexes with Cu(I) which has a high electrocatalytic reduction peak current at −0.65 V versus SCE in borate buffer (pH 9.2). In the case of AA, a complexation occurred with Cu(II) species at the electrode surface, rather than Cu(I). The electrocatalytic reduction peak current of the Cu(II)-AA complex was observed at −0.07 V in phosphate buffer at pH 6.9. Linear responses were observed in the range 2.0×10⁻⁹ to 3.0×10⁻⁸ M with a 0.9954 correlation coefficient for RS and 1.0×10⁻⁹ to 2.0×10⁻⁸ M with a 0.9961 correlation coefficient for AA.     

Preparation of silver hexacyanoferrate nanoparticles and its application for the simultaneous determination of ascorbic acid, dopamine and uric acid

A silver hexacyanoferrate nanoparticles/carbon nanotubes modified glassy carbon electrode was fabricated and then successfully used for the simultaneous determination of ascorbic acid, dopamine and uric acid by cyclic voltammetry. A detailed investigation by transmission electron microscopy (TEM) and electrochemistry was performed in order to elucidate the preparation process and properties of the nanocomposites. The size of silver hexacyanoferrate nanoparticles was examined by TEM around 27 nm. Linear calibration plots were obtained over the range of 4.0 × 10⁻⁶-7.8 × 10⁻⁵, 2.4 × 10⁻⁶-1.3 × 10⁻⁴ and 2.0 × 10⁻⁶-1.5 × 10⁻⁴ mol L⁻¹ with detection limits of 4.2 × 10⁻⁷,1.4 × 10⁻⁷ and 6.0 × 10⁻⁸ mol L⁻¹ for ascorbic acid, dopamine and uric acid, respectively. The practical analytical utilities of the modified electrode were demonstrated by the determination of ascorbic acid, dopamine and uric acid in urine and human blood serum samples.     

Antimony-film electrode for the determination of trace metals by sequential-injection analysis/anodic stripping voltammetry

The possibility of applying antimony-film modified glassy carbon electrode in sequential-injection analysis (SIA) was investigated with the objective of determining Pb(II) and Cd(II) by anodic stripping voltammetry (ASV). The conditions of antimony-film deposition concerning composition of the plating/carrier solutions, concentrations of Sb(III) and hydrochloric acid, effects of different supporting electrolyte salts, and plating potential were optimized. It was found that the antimony-film deposition on glassy carbon substrate in a sample solution consisting of 750 μg L⁻¹ Sb(III), 0.5 mol L⁻¹ HCl at −1.5 V (vs. Ag/AgCl/3 mol L⁻¹ KCl) yielded a modified electrode suitable for the determination of Pb(II) and Cd(II) at the μg L⁻¹ level. The reproducibility of the analytical signals was characterized by a relative standard deviation lower than 2.8%, and the calculated values of detection limits were 1.2 μg L⁻¹ for Pb(II) and 1.4 μg L⁻¹ for Cd(II). The presence of KSCN in the sample solution offers the possibility of detecting ions with more negative oxidation potentials like Zn(II), Mn(II) or Cr(III). The developed SIA-ASV procedure was compared with the commonly used batch method, and its applicability was tested on a spiked tap water sample.     

Amorphous carbon nitride as an alternative electrode material in electroanalysis: Simultaneous determination of dopamine and ascorbic acid

Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CN_x) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CN_x electrode. Thus, an a-CN_x film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L⁻¹ KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CN_x electrode were 0.0656 μmol L⁻¹ for DA and 1.05 μmol L⁻¹ for AA, whereas with the BDD electrode these values were 0.283 μmol L⁻¹ and 0.968 μmol L⁻¹, respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CN_x electrode in electroanalysis.     

Electrocatalytic oxidation behavior of guanosine at graphene, chitosan and Fe3O4 nanoparticles modified glassy carbon electrode and its determination

A graphene, chitosan and Fe₃O₄ nanoparticles (nano-Fe₃O₄) modified glassy carbon electrode (graphene-chitosan/nano-Fe₃O₄/GCE) was fabricated. The modified electrode was characterized by scanning electron microscope and electrochemical impedance spectroscopy. The electrochemical oxidation behavior of guanosine was investigated in pH 7.0 phosphate buffer solution by cyclic voltammetry and differential pulse voltammetry. The experimental results indicated that the modified electrode exhibited an electrocatalytic and adsorptive activities towards the oxidation of guanosine. The transfer electron number (n), transfer proton number (m) and electrochemically effective surface area (A) were calculated. Under the optimized conditions, the oxidation peak current was proportional to guanosine concentration in the range of 2.0 × 10⁻⁶ to 3.5 × 10⁻⁴ mol L⁻¹ with the correlation coefficient of 0.9939 and the detection limit of 7.5 × 10⁻⁷ mol L⁻¹ (S/N = 3). Moreover, the modified electrode showed good ability to discriminate the electrochemical oxidation response of guanosine, guanine and adenosine. The proposed method was further applied to determine guanosine in spiked urine samples and traditional Chinese medicines with satisfactory results.     

Simultaneous determination of antioxidants at a chemically modified electrode with vitamin B12 by capillary zone electrophoresis coupled with amperometric detection

In the paper, a new kind of vitamin B₁₂ (acquo-cobalamine) chemically modified electrode was fabricated and applied in capillary zone electrophoresis coupled with amperometric detection (CZE-AD) for simultaneous determination of six antioxidants in fruits and vegetables. The catalytic electrochemical properties of the chemically modified electrode could obviously enhance oxidation peak heights responses by about five times to glutathione, ascorbic acid, vanillic acid, chlorogenic acid, salicylic acid, and caffeic acid compared with common carbon disk electrode. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Under the optimum conditions, the six analytes could be completely separated and detected in a borate-phosphate buffer (pH 8.4) within 15 min. Their linear ranges were from 2.5 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ and the detection limits were as low as 10⁻⁸ mol L⁻¹ magnitude (S/N = 3). The proposed method has been successfully employed to monitor the six analytes in practical samples with recoveries in the range 96.0-106.0% and RSDs less than 5.0%. Above results demonstrate that capillary zone electrophoresis coupled with electrochemical detection using vitamin B₁₂ modified electrode as detector is of convenient preparation, high sensitivity, good repeatability, and could be used in the rapid determination of practical samples.     

Simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using a carbon composite electrode modified with Cu3(PO4)2 immobilized in polyester resin

A simple electrochemical method was developed for the single and simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using square-wave voltammetry (SWV). A carbon composite electrode modified (MCCE) with copper (II) phosphate immobilized in a polyester resin was proposed. The modified electrode allowed the detection of BHA and BHT at potentials lower than those observed at unmodified electrodes. A separation of about 430 mV between the peak oxidation potentials of BHA and BHT in binary mixtures was obtained. The calibration curves for the simultaneous determination of BHA and BHT demonstrated an excellent linear response in the range from 3.4 × 10⁻⁷ to 4.1 × 10⁻⁵ mol L⁻¹ for both compounds. The detection limits for the simultaneous determination of BHA and BHT were 7.2 × 10⁻⁸ and 9.3 × 10⁻⁸ mol L⁻¹, respectively. In addition, the stability and repeatability of the electrode were determined. The proposed method was successfully applied in the simultaneous determination of BHA and BHT in several food samples, and the results obtained were found to be similar to those obtained using the high performance liquid chromatography method with agreement at 95% confidence level.     

Flow injection fluorometric determination of ascorbic acid using perylenebisimide-linked nitroxide

A simple and sensitive flow injection fluorometric method for the determination of ascorbic acid is described. Perylenebisimide-linked nitroxide (PBILN) is used as a fluorescent reagent, which permits the selective determination of ascorbic acid. The fluorescence of the perylenebisimide moiety in PBILN is quenched by the nitroxide moiety, which is linked to the perylenebisimide. When a stream of a solution of ascorbic acid is merged with a stream of PBILN, the ascorbic acid reacts with the nitroxide moiety of PBILN to form hydroxylamine, and the fluorescence properties of the perylenebisimide moiety are recovered. As a result, a peak-shaped fluorescence signal is produced, which can be observed by a fluorescence detector located downstream. Under optimized conditions, a good linear relationship between the concentration of ascorbic acid and peak height in the concentration range from 0.5 to 10 μmol L⁻¹ was found and the detection limit (S/N = 3) was 0.28 μmol L⁻¹. The relative standard deviation for the determination of 4.0 μmol L⁻¹ ascorbic acid samples was 1.0% (n = 5). The proposed method was applied to the determination of ascorbic acid in several soft drink beverages and the analytical results were in good agreement with those obtained using a conventional method.     

Fabrication of a highly sensitive electrochemiluminescence lactate biosensor using ZnO nanoparticles decorated multiwalled carbon nanotubes

ZnO nanoparticles (nanoZnO) were decorated on multiwalled carbon nanotubes (MWCNTs) and then the prepared nano-hybrids, nanoZnO-MWCNTs, were immobilized on the surface of a glassy carbon electrode (GCE) to fabricate nanoZnO-MWCNTs modified GCE. The prepared electrode, GCE/nanoZnO-MWCNTs, showed excellent electrocatalytic activity towards luminol electrochemiluminescence (ECL) reaction. The electrode was then further modified with lactate oxidase and Nafion to fabricate a highly sensitive ECL lactate biosensor. Two linear dynamic ranges of 0.01-10 μmol L⁻¹ and 10-200 μmol L⁻¹ were obtained for lactate with the correlation coefficient better than 0.9996. The detection limit (S/N = 3) was 4 nmol L⁻¹ lactate. The relative standard deviation for repetitive measurements (n = 6) of 10 μmol L⁻¹ lactate was 1.5%. The fabrication reproducibility for five biosensors prepared and used in different days was 7.4%. The proposed ECL lactate biosensor was used for determination of lactate in human blood plasma samples with satisfactory results.     

Determination of chlorogenic acid in coffee using a biomimetic sensor based on a new tetranuclear copper(II) complex

A new tetranuclear copper(II) complex which mimics the active site of catechol oxidase was synthesized and characterized by IR, CHN, electronic spectroscopic and ¹H NMR methods. The title complex [Cu₂(μ-OH)(bpbpmp-NO₂)]₂[ClO₄]₂ was employed in the construction of a novel biomimetic sensor and used in the determination of chlorogenic acid by square wave voltammetry. The performance and optimization of the resulting biomimetic sensor were studied in detail. The best response of this sensor was obtained for 75:15:10% (w/w/w) ratio of the graphite powder:nujol:Cu(II) complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 7.0), with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 3.0 mV, respectively. The chlorogenic acid concentration was linear in the range of 5.0 × 10⁻⁶ to 1.45 × 10⁻⁴ mol L⁻¹ (r = 0.9985) with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹. This biomimetic sensor demonstrated long-term stability (250 days; 640 determinations) and reproducibility, with a relative standard deviation of 10.0%. The recovery study of chlorogenic acid in coffee samples gave values from 93.2% to 106.1% and the concentrations determined showed good agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level.     

Simultaneous voltammetric detection of ascorbic acid, dopamine and uric acid using a pyrolytic graphite electrode modified into dopamine solution

Pyrolytic graphite electrodes (PGE) were modified into dopamine solutions using phosphate buffer solutions, pH 10 and 6.5, as supporting electrolyte. The modification process involved a previous anodization of the working electrode at +1.5 V into 0.1 mol L⁻¹ NaOH followed by other anodization step, in the same experimental conditions, into dopamine (DA) solutions. pH of the supporting electrolyte performed an important role in the production of a superficial melanin polymeric film, which permitted the simultaneous detection of ascorbic acid (AA), (DA) and uric acid (UA), ΔE_AA-DA = 222 mV; ΔE_AA-UA = 360 mV and ΔE_DA-UA = 138 mV, avoiding the superficial poisoning effects. The calculated detection limits were: 1.4 × 10⁻⁶ mol L⁻¹ for uric acid, 1.3 × 10⁻⁵ mol L⁻¹ for ascorbic acid and 1.1 × 10⁻⁷ mol L⁻¹ for dopamine, with sensitivities of (7.7 ± 0.5), (0.061 ± 0.001) and (9.5 ± 0.05) A mol⁻¹ cm⁻², respectively, with no mutual interference. Uric acid was determined in urine, blood and serum human samples after dilution in phosphate buffer and no additional sample pre-treatment was necessary. The concentration of uric acid in urine was higher than the values found in blood and serum and the recovery tests (92-102%) indicated that no matrix effects were observed.     

Differential pulse voltammetric simultaneous determination of noradrenalin and acetaminophen using a hematoxylin biosensor

A highly efficient noradrenalin (NA) biosensor was fabricated on the basis of hematoxylin electrodeposited on a glassy carbon electrode, GCE. The cyclic voltammetric responses of the hematoxylin biosensor at various scan rates, which were obtained in a 0.25 mmol L⁻¹ NA solution, showed the characteristic shape typical of an EC_cat process. The kinetic parameters such as electron transfer coefficient, α, the catalytic electron transfer rate constant, k′, and the standard catalytic electron transfer rate constant, k⁰, for oxidation of NA at the hematoxylin biosensor surface were estimated using cyclic and RDE voltammetry. The peaks of differential pulse voltammetric (DPV) for NA and acetaminophen (AC) oxidation at the hematoxylin biosensor surface were clearly separated from each other when they co-exited in the physiological pH (pH 7.0). It was, therefore, possible to simultaneously determine NA and AC in the samples at a hematoxylin biosensor. Linear calibration curves were obtained for 5.0 × 10⁻¹ to 65.40 μmol L⁻¹ and 65.40-274.20 μmol L⁻¹ of NA, and for 12.00-59.10 μmol L⁻¹ and 59.10-261.70 μmol L⁻¹ of AC. The sensitivities of the biosensor to NA in the absence and presence of AC were found virtually the same, which indicates the fact that the electrocatalytic oxidation processes of NA are independent of AC and, therefore, simultaneous or independent measurements of the two analytes (NA and AC) are possible without any interference. The results of 16 successive measurements show an average voltammetric peak current of 1.13 ± 0.03 μA for an electrolyte solution containing 5.00 μmol L⁻¹ NA. The hematoxylin biosensor has been satisfactorily used for the determination of NA and AC in pharmaceutical formulations. The results obtained, using the biosensor, are in very good agreement with those declared in the label of pharmaceutical inhalation products.     

The use of a gold disc microelectrode for the determination of copper in human sweat

A novel approach of using a gold disc microelectrode to analyze sweat samples for copper ions by anodic square wave stripping voltammetry (SW stripping voltammetry) is described. Sweat was collected from the lower back of four subjects after physical exercise and the sample volume required for the determinations was 100 μL. Under the optimized conditions, the calibration plot was linear over the range 1-100 μmol L⁻¹ Cu(II) with a limit of detection of 0.25 μmol L⁻¹. The precision was evaluated by carrying out five replicate measurements in a 1 μmol L⁻¹ Cu(II) solution and the standard deviation was found to be 1.5%. Measurements were performed by inserting the microelectrode into sweat drops and Cu(II) concentrations in the analyzed samples ranged from 0.9 to 28 μmol L⁻¹. Values obtained by the proposed voltammetric method agreed well with those found using graphite furnace atomic absorption spectroscopy (GFAAS).     

Highly selective and sensitive copper membrane electrode based on a new synthesized Schiff base

Bis(2-hydroxyacetophenone)butane-2,3-dihydrazone (BHAB) was used as new N-N Schiffs base which plays the role of an excellent ion carrier in the construction of a Cu(II) membrane sensor. The best performance was obtained with a membrane composition of 30% poly(vinyl chloride), 55% o-nitrophenyloctyl ether (NPOE), 7% BHAB and 8% oleic acid (OA). This sensor shows very good selectivity and sensitivity towards copper ion over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The effect of membrane composition and pH and influence of additive anionic on the response properties of electrode were investigated. The electrode exhibits a Nernstian behavior (with slope of 29.6 mV per decade) over a very wide concentration range (5.0 × 10⁻⁸ to 1.0 × 10⁻² mol L⁻¹) with a detection limit of 3.0 × 10⁻⁸ mol L⁻¹ (2.56 ng mL⁻¹). It shows relatively fast response time, in whole concentration range (<15 s), and can be used for at least 12 weeks in the pH range of 2.8-5.8. The proposed sensor was successfully used to determination of copper in different water samples and as indicator electrode in potentiometric titration of copper ion with EDTA.     

Selective electrochemical sensing of calcium dobesilate based on the nano-Pd/CNTs modified pyrolytic graphite electrode

A new palladium nanoparticle functionalized multi-wall carbon nanotubes (nano-Pd/CNTs) modified pyrolytic graphite electrode (PGE) has been fabricated for electrochemical sensing of calcium dobesilate (CD) in pharmaceutical capsules. The nano-Pd/CNTs were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The nano-Pd/CNTs composite showed a strong electrocatalytic property for CD. The anodic peak current is 6-fold than that obtained in bare PGE and the oxidation potential has an obvious shift to negative. The anodic peak current is proportional to the concentration of CD in the range of 1.0 × 10⁻⁷ to 7.0 × 10⁻⁴ mol L⁻¹, with a linear relative coefficient r = 0.999 and a detection limit 4.0 × 10⁻⁸ mol L⁻¹ (S/N = 3). This kind of electrode shows good stability, sensitivity, reproducibility, large linear range and low detection limit towards electrochemical determination of CD. The proposed method provides a selective and sensitive electrochemical sensor of calcium dobesilate.