Emerson Ribeiro - Academia.edu (original) (raw)

Papers by Emerson Ribeiro

Revista Arvore, 2004

Acacia holosericea is a leguminous species that has been extensively used in land reclamation pro... more Acacia holosericea is a leguminous species that has been extensively used in land reclamation programs. The knowledge of its nutritional symptoms allows the identification and correction of deficiencies in individuals planted in degraded substrates. The aim of this work was to characterize the behavior of seedlings of A. holosericea submitted to different nutritional solutions with absence of macronutrients. The treatments consisted of seven nutritional solutions: 1) Complete solution (SC); 2) SC - N; 3) SC -P; 4) SC -K; 5) SC -Ca; 6) SC -Mg; 7) SC -S. Treatments -N and -Mg were the ones that most affected biomass production. Decrease in biomass production occurred in the following order: -N = -Mg > -K > -S > -Ca > SC > -P. The -N treatment plants formed nodules in their roots, showing higher concentrations of N than those of the SC treatment. Except for the SC and -P treatments, all the other treatments showed nutritional deficiency symptoms. The absence of S has led to a change in the natural disposition of new leaves of A. holosericea.

Biometals, 2009

The interaction of Pt(II)(dppf)-complex, namely [Pt(dppf)(H2O)2]2+ with DNA was investigated by D... more The interaction of Pt(II)(dppf)-complex, namely [Pt(dppf)(H2O)2]2+ with DNA was investigated by DPV and 1H-NMR techniques. The results showed that the interaction process has been characterized by changes in the electrochemical parameters of both compounds and the formation of a new anodic current peak close to the anodic current peak of the [Pt(dppf)(H2O)2]2+. In addition, the 1H-NMR spectra show that the coordination of Pt(II)(dppf)-complex to dsDNA occurs via N(7) of guanine. Others parameters like pH and ionic strength that affect the interaction process were also investigated.

Quimica Nova, 2006

The adsorption capacity of a-chitosan and its modified form with succinic anhydride was compared ... more The adsorption capacity of a-chitosan and its modified form with succinic anhydride was compared with the traditional adsorbent active carbon by using the dye methylene blue, employed in the textile industry. The isotherms for both biopolymers were classified as SSA systems in the Giles model, more specifically in L class and subgroup 3. The dye concentration in the supernatant in the adsorption assay was determined through electronic spectroscopy. By calorimetric titration thermodynamic data of the interaction between methyene blue and the chemically modified chitosan at the solid/liquid interface were obtained. The enthalpy of the dye/chitosan interaction gave 2.47 ± 0.02 kJ mol-1 with an equilibrium constant of 7350 ± 10 and for the carbon/dye interaction this constant gave 5951 ± 8. The spontaneity of these adsorptions are reflected by the free Gibbs energies of -22.1 ± 0.4 and -21.5 ± 0.2 kJ mol-1, respectively, found for these systems. This new adsorbent derived from a natural polysaccharide is as efficient as activated carbon. However 97% of the bonded dye can be eluted by sodium chloride solution, while this same operation elutes only 42% from carbon. Chitosan is efficient in dye removal with the additional advantage of being cheap, non-toxic, biocompatible and biodegradable.

Journal of Electroanalytical Chemistry, 2002

Hematoporphyrin IX (8,13-bis(1-hydroxyethyl)-3,7,12,17-tetramethyl-21H-23H-porphine-2,18-dipropio... more Hematoporphyrin IX (8,13-bis(1-hydroxyethyl)-3,7,12,17-tetramethyl-21H-23H-porphine-2,18-dipropionic acid) and protoporphyrin IX (8,13-divinyl-3,7,12,17-tetramethyl-21H-23H-porphine-2,18-dipropionic acid) were efficiently immobilized on a cellulose/titanium (IV) oxide composite fiber surface by the reaction of the porphyrin COOH groups with TiO2, presumably by forming the COOTi chemical bond. Furthermore, Co(II) was incorporated into the porphyrin ring, with this reaction being followed by UV–vis spectra in the solid state and confirmed by the change of the absorption bands due to a local symmetry change from D2h to D4h upon metallation of the porphyrin ring. Electrochemical studies by using cyclic voltammetry and chronoamperometry techniques, showed that the immobilized complexes catalyzed O2 reduction at −0.18 V for hematoporphyrin and −0.20 V for protoporphyrin in 1 mol l−1 KCl solution at pH 6. The cathodic current peak intensities plotted against O2 concentrations in the range from 0.5 to 13 mg l−1, showed a linear correlation. Rotating disk experiments were carried out in order to estimate the number of electrons involved on the process. It was observed that for both modified electrodes, dissolved O2 was reduced to H2O2 in a two-electron process.

Mikrochimica Acta, 2006

Hexacyanoferrate (II/III) (HCF) was immobilized on a gold electrode modified with cysteamine (CST... more Hexacyanoferrate (II/III) (HCF) was immobilized on a gold electrode modified with cysteamine (CSTE). The Au/CSTE/HCF/PLL electrode was prepared with layer-by-layer (LBL) technique with HCF and poly-d-lysine (PLL). The Au/CSTE/HCF/PLL electrode presented the electrocatalytic activity for ascorbic acid oxidation. The maximum electrocatalytic current was reached at 0.28 V vs SCE in 0.01 mol L−1 TRIS buffer, at pH 7.0. The Au/CSTE/HCF/PLL electrode response was stable under various oxidation–reduction cycles in TRIS medium, showing that the system is very stable. The solution pH has no effect on the anodic peak potential and anodic peak current in the range from 4 up to 10. The intensity of the anodic peak current varied with the concentration of ascorbic acid from 1 up to 910 µmol L−1, with a sensitivity of 62.9 nA cm−2 L µmol−1, a detection limit of 0.65 µmol L−1 and a quantification limit of 2.2 µmol L−1. The developed sensor was successfully applied for ascorbic acid determination in pharmaceutical samples. The results compared to those obtained with a reference method were statistically the same with 95% of confidence level.

Journal of Porphyrins and Phthalocyanines, 2002

Abstract: Electrochemical reduction of dioxygen on an iron (III)-tetra-o-ureaphenylporphyrino-sil... more Abstract: Electrochemical reduction of dioxygen on an iron (III)-tetra-o-ureaphenylporphyrino-silica matrix surface ((o)-FeTUPPS) obtained by attachment of the iron porphyrin tetraurea to a silica matrix through the sol-gel process was studied. Cyclic voltammetry and ...

Electrochimica Acta, 2004

In this work, SiO2/Sb2O3 prepared by the sol–gel processing method, having a specific surface are... more In this work, SiO2/Sb2O3 prepared by the sol–gel processing method, having a specific surface area, SBET, of 790 m2 g−1, an average pore diameter of 1.9 nm and 4.7 wt.% of Sb, was used as substrate base for immobilization of the 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine ion. Cobalt(II) ion was inserted into the porphyrin ring with a yield of complex bonded to the substrate surface of 59.4 μ mol g−1. A carbon paste electrode of this material was used to study, by linear sweeping voltammetric and chronoamperometric techniques, the electrocatalytic reduction of dissolved oxygen. The reduction, at the electrode solid–solution interface, occurred at −0.25 V versus SCE in 1.0 mol l−1 KCl solution, pH 5.5, by a four electron mechanism. The electrode response was invariant under various oxidation–reduction cycles showing that the system is chemically very stable. Such characteristics allowed the study of the electrode response towards various dissolved oxygen concentrations using the chronoamperometry technique. The cathodic peak current intensities plotted against O2 concentrations, between 1.0 and 12.8 mg l−1, showed a linear correlation. The electrode response time was very fast, i.e. about 1 s. This study was extended using the electrode to determine the concentration of dissolved oxygen in sea water samples.

Electrochimica Acta, 1999

Iron (II) tetrasulphophthalocyanine complex was adsorbed on a 3-n-propylpyridinium chloride funct... more Iron (II) tetrasulphophthalocyanine complex was adsorbed on a 3-n-propylpyridinium chloride functionalized silica gel surface by means an ion exchange reaction. The amount of the complex bonded to the substrate surface, by electrostatic interaction, is 25 μmol g−1 and the specific surface area SBET=320 m2 g−1. A carbon paste electrode made with the material can electrocatalytically reduce dissolved oxygen to water at a potential Epc=−140 mV in 0.5 M KCl solution. The plot of the cathodic current against dissolved oxygen concentrations between 0.65 and 14.4 mg dm−3 showed a linear correlation at 298 K and pH 5. The electrode presented a reproducible response and chemically it was stable under various oxidation–reduction cycles.

Reactive and Functional Polymers, 2014

ABSTRACT A novel hierarchically imprinted cross-linked poly(acrylamide-co-ethylene glycol dimetha... more ABSTRACT A novel hierarchically imprinted cross-linked poly(acrylamide-co-ethylene glycol dimethacrylate) using a double-imprinting approach for the Cu2+ selective separation from aqueous medium was prepared. In the imprinting process, both Cu2+ ions and surfactant micelles (cetyltrimethylammonium bromide - CTAB) were employed as templates. The hierarchically imprinted organic polymer named (IIP-CTAB), single-imprinted (IIP-no CTAB) and non-imprinted (NIP-CTAB and NIP-no CTAB) polymers were characterized by SEM, FTIR, TG, elemental analysis and textural data from BET (Brunauer–Emmett–Teller) and BJH (Barrett-Joyner-Halenda). Compared to these materials, IIP-CTAB showed higher selectivity, specific surface area and adsorption capacity towards Cu2+ ions. Good selectivity for Cu2+ was obtained for the Cu2+/Cd2+, Cu2+/Zn2+ Cu2+/Co2+ systems when IIP-CTAB was compared to the single-imprinted (IIP-no CTAB) and non double-imprinted polymer (NIP-CTAB), thereby confirming the improvement in the polymer selectivity due to double-imprinting effect. For adsorption kinetic data, the best fit was provided with the pseudo-second-order model for the four materials, thereby indicating the chemical nature of the Cu2+ adsorption process. Cu2+ adsorption under equilibrium was found to follow dual-site Langmuir-Freundlich model isotherm, thus suggesting the existence of adsorption sites with low and high binding energy on the adsorbent surface. From column experiments 600 adsorption-desorption cycles using 1.8 mol L-1 HNO3 as eluent confirmed the great recoverability of adsorbent. The synthesis approach here investigated has been found to be very attractive for the designing of organic ion imprinted polymer and can be expanded to the other polymers to improve performance of ion imprinted polymers in the field of solid phase extraction.

Microchemical Journal, 2014

ABSTRACT A redox speciation and preconcentration study of Cr(III) and Cr(VI) using a flow injecti... more ABSTRACT A redox speciation and preconcentration study of Cr(III) and Cr(VI) using a flow injection system with dual mini-columns prepared from cross-linked polymers - poly(methacrylic acid) and polyvinylimidazole was developed. Characterization of organic polymers were performed by using FTIR, SEM, TG, C:H:N and BET measurements. The equilibrium data obtained from Cr(III) adsorption on poly(methacrylic acid) and Cr(VI) on polyvinylimidazole were fitted very well to the dual site Langmuir-Freundlich model, suggesting the presence homogeneous and heterogeneous binding site and providing maximum adsorption capacities of 1.42 and 3.24 mg g- 1, respectively. The adsorption kinetics data were described by the pseudo-second-order model for both polymers, thus corroborating to isotherm data. The on-line preconcentration/speciation system was operated by loading 18.0 mL of a solution containing Cr(III) and Cr(VI) at pH 4.0 through the dual mini-columns at a flow rate of 3.0 mL min- 1, where Cr(III) was selectively retained on poly(methacrylic acid), whilst Cr(VI) was retained on polyvinylimidazole . The limits of detection were found to be 0.84 and 1.58 μg L- 1 for Cr(III) and Cr(VI), respectively. The preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were found to be 47.3/8.6, 0.38/2.1 mL and 7.88/1.43 min- 1 for Cr(III) and Cr(VI), respectively. The developed method was successfully applied to the speciation of chromium in different kinds of water samples. Satisfactory recovery values ranging from 89.9 to 108.3% were obtained.

Matéria (Rio de Janeiro), 2013

Os óxidos mistos SiO 2 /M x O y obtidos pelo processo sol-gel, designados de compósitos, normalme... more Os óxidos mistos SiO 2 /M x O y obtidos pelo processo sol-gel, designados de compósitos, normalmente aliam as propriedades mecânicas e químicas da sílica gel com as propriedades químicas do óxido metálico (M x O y ), apresentando propriedades tais como: elevado grau de dispersão e homogeneidade das partículas do óxido metálico na matriz de sílica, assim como elevada resistência mecânica e química. O objetivo deste trabalho foi o de preparar e caracterizar materiais do sistema SiO 2 /Mn x O y , obtidos pelo processo sol-gel, utilizando diferentes concentrações dos precursores de Mn (II), acetato ou nitrato. A técnica de fluorescência de raios X (FRX) mostrou que a concentração do óxido metálico nos materiais é dependente do precursor utilizado e da sua concentração no meio reacional, variando de 9,4% até 20,9% em massa. A maior concentração de óxido de manganês foi obtida quando se utilizou como precursor o (CH 3 CO 2 ) 2 Mn.4H 2 O. Os espectros de infravermelho indicam que a rede de SiO 2 é pouco perturbada pelo aumento da quantidade de óxido de manganês, sugerindo que o Mn x O y está disperso na superfície da matriz de sílica. Os difratogramas de raiosX (DRX) mostram que os materiais apresentam baixa cristalinidade. No entanto, observa-se uma mudança no DRX em 2θ = 35,7 o quando o material é aquecido a 400 0 C, provavelmente devido à formação de cristalitos de Mn 3 O 4 . O método de síntese proposto para os materiais SiO 2 /Mn x O y é reprodutível. A aplicação destes materiais como eletrodos para a redução de O 2 foi avaliada e observou-se que a atividade eletrocatalítica desses materiais pode ser aumentada através do seu aquecimento a 400 0 C.

Journal of The Brazilian Chemical Society, 2007

The electrochemical properties of meldola blue and toluidine blue cationic dyes immobilized on ce... more The electrochemical properties of meldola blue and toluidine blue cationic dyes immobilized on cellulose acetate surface modified with titanium dioxide were investigated by cyclic voltammetry. The materials synthesized were employed as carbon paste electrodes. The redox mediator properties of the meldola blue and toluidine blue chemically modified electrodes were optimized using a factorial design, consisting of two levels and four factors with two pseudo-central points (n= 20 experiments). The factorial analysis was carried out by searching for better reversibility of the redox process, such as the lowest separation between anodic and cathodic potential peaks and a current ratio near unity. The factors that presented significant effects on the overall optimization of the system to achieve the best conditions of the reversibility of electron transfer were the main factors scan rate and type of electrode (meldola blue or toluidine blue), besides the interaction factors KCl concentration × type of electrode (B×D) and the pH × [KCl] concentration × scan rate (A×B×C) interaction. The best electrochemical reversibility conditions obtained were: using the CA-TiO2-MB electrode, 1.0 mol L-1 KCl as supporting electrolyte, at scan rate of 10.0 mV s-1. Afterwards, the CA-TiO2-MB modified electrode was tested as an amperometric sensor for the determination of NADH, with a detection limit of 0.1 µmol L-1.

Clean-soil Air Water, 2010

Activated carbon materials were prepared from the Brazilian pine-fruit shell (Araucaria angustifo... more Activated carbon materials were prepared from the Brazilian pine-fruit shell (Araucaria angustifolia) by chemically activated carbon (CAC) and chemically and physically activated carbon (CPAC), and tested as adsorbents for the removal of brilliant green (BG) dye from aqueous effluents. The mixed activation process leads to increases in the specific surface area, average porous volume, and average porous diameter of the adsorbent CPAC when compared to CAC. The effects of shaking time, adsorbent dosage and pH on the adsorption capacity were studied. BG uptake was favorable at pH values ranging from 2.0 to 10.0 for both CAC and CPAC. The contact time required to obtain the equilibrium using CAC and CPAC as adsorbents was 4 h at 298 K, respectively. The fractionary-order kinetic model provided the best fit to experimental data compared with other models. Equilibrium data were better fit to the Sips and Redlich-Peterson isotherm models using CAC and CPAC as adsorbents. The enthalpy and entropy of adsorption of BG were obtained from adsorption experiments ranging from 298 to 323 K.

Talanta, 2012

In the present study, a flow injection system using dual mini-columns, SiO 2 /Al 2 O 3 /TiO 2 and... more In the present study, a flow injection system using dual mini-columns, SiO 2 /Al 2 O 3 /TiO 2 and silica gel functionalized with [3-(2-aminoethylamino)propyl] trimethoxysilane (SiO 2 /AAPTMS) for the sequential preconcentration of Cr(III) and Cr(VI), respectively, from water samples with FAAS detection was proposed. A two-level full factorial design (2 4 ) and desirability function were employed for the optimization of variables related to the system performance. The detection limits of 0.66 and 0.27 mg L À 1 for Cr(III) and Cr(IV), respectively, were obtained under the optimized preconcentration conditions (flow rate of 7.0 mL min À 1 ), pH 5.0, buffer concentration (acetate buffer) of 0.01 mol L À 1 , and eluent (2.5 mol L À 1 HCl) flow rate of 5.0 mL min À 1 . The other parameters including preconcentration factor (PF), consumptive index (CI), and concentration efficiency (CE) were found to be 17.62/32.98, 1.13/0.6 mL, and 6.2/11.54 min À 1 for Cr(III)/Cr(VI), respectively. The developed method was applied to the Cr(III) and Cr(VI) determination in water samples [tap, lake and mineral water, artificial saliva and parenteral solutions (physiological serum, water for injection, and glucose physiological solution)]. The method accuracy was checked by the analysis of standard reference materials (trace elements in water).

Sensors and Actuators B: Chemical, 2013

ABSTRACT A simple voltammetric method based on a composite biosensor MWCN/SiO2/Al2O3/Nb2O5/DNA (M... more ABSTRACT A simple voltammetric method based on a composite biosensor MWCN/SiO2/Al2O3/Nb2O5/DNA (MWCN/SiAlNb/DNA) was developed and validated for the determination of promethazine (PHZ) in raw material and pharmaceutical formulation. The best results were obtained by using square wave voltammetry under measurements at 0.30 mol L−1 phosphate buffer pH 7.0 and DNA immobilization onto SiAlNb surface using 0.8 mg mL−1 concentration. Validation parameters such as: selectivity, linearity, precision, accuracy, and stability presented results within the acceptable range. The sensitivity of sensor was found to be 0.210 μA μmol−1 L. Therefore, the developed method was successfully applied for the PHZ determination in real samples of pharmaceutical formulations and can be used for routine quality control analysis of bulk pharmaceutical and pharmaceutical formulations containing PHZ.

Talanta, 2011

The present paper describes the synthesis of a new chemically modified cellulose microfiber throu... more The present paper describes the synthesis of a new chemically modified cellulose microfiber through oxidation with sodium periodate and functionalization with N,N′-bis (2-aminoethyl)-1,2-ethanediamine for the fast and selective preconcentration of Cd(II) ions in flow system analysis. The new sorbentsorbent was characterized by FTIR, SEM, and surface area values. The uptake behavior of Cd(II) ions onto this sorbent was evaluated from kinetic data, pseudo-first-order and pseudo-second-order models, as well as from Langmuir, Freundlich and Langmuir–Freundlich adsorption isotherms. The maximum sorption capacity of 4.59 mg g−1 was estimated by the Langmuir–Freundlich model with fast kinetics for the sorption of Cd(II) described by the pseudo-second-order kinetic model. After characterization, the sorbent was packed in a mini-column, and a fast flow injection preconcentration system for Cd(II) determination by FAAS was developed. The best Cd(II) preconcentration condition, obtained by means of factorial design and response surface methodology, was achieved at pH 9.36 and a flow rate of 10 mL min−1 followed by elution with 1.0 mol L−1 nitric acid. By using 78 s preconcentration time, fast and highly sensitive determination of Cd(II) ions could be achieved with a limit of quantification of 0.20 μg L−1, preconcentration factor of 26, consumption index of 0.5 mL, concentration efficiency of 20 min−1, and sample throughput of 39 h−1. The repeatability for 10 replicate determinations was found to be 7.8 and 2.5% for Cd(II) ion concentrations of 5.0 and 100.0 μg L−1, respectively. The new sorbent efficiency for the interference-free preconcentration of Cd(II) ions was assessed by analysis of tap, mineral and lake waters, as well as synthetic seawater and normal saline waters. Furthermore, complex samples, such as biological samples, could be analysed by the proposed method in accordance with the accuracy attested by analysis of certified reference materials, TORT-2 (lobster hepatopancreas), and DOLT-4 (dogfish liver).

Química Nova, 2006

Recebido em 13/4/05; aceito em 29/8/05; publicado na web em 8/2/06 THE USE OF CHEMICALLY MODIFIED... more Recebido em 13/4/05; aceito em 29/8/05; publicado na web em 8/2/06 THE USE OF CHEMICALLY MODIFIED CHITOSAN WITH SUCCINIC ANHYDRIDE IN THE METHYLENE BLUE ADSORPTION. The adsorption capacity of α-chitosan and its modified form with succinic anhydride was compared with the traditional adsorbent active carbon by using the dye methylene blue, employed in the textile industry. The isotherms for both biopolymers were classified as SSA systems in the Giles model, more specifically in L class and subgroup 3. The dye concentration in the supernatant in the adsorption assay was determined through electronic spectroscopy. By calorimetric titration thermodynamic data of the interaction between methyene blue and the chemically modified chitosan at the solid/liquid interface were obtained. The enthalpy of the dye/chitosan interaction gave 2.47 ± 0.02 kJ mol -1 with an equilibrium constant of 7350 ± 10 and for the carbon/dye interaction this constant gave 5951 ± 8. The spontaneity of these adsorptions are reflected by the free Gibbs energies of -22.1 ± 0.4 and -21.5 ± 0.2 kJ mol -1 , respectively, found for these systems. This new adsorbent derived from a natural polysaccharide is as efficient as activated carbon. However 97% of the bonded dye can be eluted by sodium chloride solution, while this same operation elutes only 42% from carbon. Chitosan is efficient in dye removal with the additional advantage of being cheap, non-toxic, biocompatible and biodegradable.

Microchimica Acta, 2012

ABSTRACT We describe the analytical performance of a hybrid material composed of SiO2, Al2O3 and ... more ABSTRACT We describe the analytical performance of a hybrid material composed of SiO2, Al2O3 and TiO2. It was prepared by a sol–gel process and can act as an adsorbent in the continuous-flow enrichment of copper. A minicolumn was packed with the material, copper ions are adsorbed at pH 9.13, then eluted with 1.0 mol L−1 nitric acid, and determined by FAAS. The material was characterized by infrared spectroscopy, scanning electron and energy dispersive spectroscopy, energy dispersive X-ray fluorescence analysis, powder X-ray diffraction, and specific surface area analysis. No significant interference was observed for most ions in up to copper/interferent ratios of 1:100 and of 1:500 in case of Ca(II), Ba(II), and Mg(II). The breakthrough capacity is 1.4 mg g−1 under dynamic conditions. The limits of detection and of quantification are 0.50 and 1.4 μg L−1, respectively, and the calibration plot is linear in the range from 5.0 to 245.0 μg L−1 (r = 0.999). The relative standard deviation is 3.20 (for n = 7 and at a Cu(II) concentration of 10 μg L−1). The method was applied to the determination of trace copper ions in water, vegetable and alcohol fuel samples. Figure We describe the analytical performance of the hybrid material composed of SiO2, Al2O3 and TiO2. It was prepared by a sol–gel process and can act as an adsorbent in the continuous-flow enrichment of copper. The method was applied to the determination of trace copper ions in water, vegetable and alcohol fuel samples.

Microchimica Acta, 2006

Hexacyanoferrate (II=III) (HCF) was immobilized on a gold electrode modified with cysteamine (CST... more Hexacyanoferrate (II=III) (HCF) was immobilized on a gold electrode modified with cysteamine (CSTE). The Au=CSTE=HCF=PLL electrode was prepared with layer-by-layer (LBL) technique with HCF and poly-D-lysine (PLL). The Au=CSTE= HCF=PLL electrode presented the electrocatalytic activity for ascorbic acid oxidation. The maximum electrocatalytic current was reached at 0.28 V vs SCE in 0.01 mol L À1 TRIS buffer, at pH 7.0. The Au= CSTE=HCF=PLL electrode response was stable under various oxidation-reduction cycles in TRIS medium, showing that the system is very stable. The solution pH has no effect on the anodic peak potential and anodic peak current in the range from 4 up to 10. The intensity of the anodic peak current varied with the concentration of ascorbic acid from 1 up to 910 mmol L À1 , with a sensitivity of 62.9 nA cm À2 L mmol À1 , a detection limit of 0.65 mmol L À1 and a quantification limit of 2.2 mmol L À1 . The developed sensor was successfully applied for ascorbic acid determination in pharmaceutical samples. The results compared to those obtained with a reference method were statistically the same with 95% of confidence level.