RESUMO
A novel voltammetric screening method has been developed for the rapid determination of fipronil (FPN) residues in lactose-free milk samples with the use of a carbon-paste electrode (CPE) by differential-pulse voltammetry (DPV). Cyclic voltammetry indicated the occurrence of an irreversible anodic process at approximately +0.700 V (vs. Ag|AgCl, 3.0 mol L-1 KCl) in a 0.100 mol L-1 NaOH supporting electrolyte prepared as a 30% (v/v) ethanol-water solution. Quantification of FPN was carried out by DPV and analytical curves were constructed. In the absence of a matrix, the limits of detection (LOD) and quantification (LOQ) were 0.568 mg L-1 and 1.89 mg L-1, respectively. In the presence of a lactose-free skim milk matrix, the values of LOD and LOQ were 0.331 mg L-1 and 1.10 mg L-1. The recovery percentages for three different concentrations of FPN in lactose-free skim milk samples ranged between 95.3% and 109%. All assays could be conducted with milk samples without any prior extraction steps or pre-concentration of FPN, making this novel method rapid, simple, and relatively cheap.
Assuntos
Carbono , Leite , Animais , Bovinos , Carbono/química , Eletroquímica/métodos , EletrodosRESUMO
Hydroquinone is a skin-lightening agent used as an active ingredient in topical dermatological formulations prescribed for treating cutaneous diseases caused by hyperpigmentation. Despite being widely used, some toxicological aspects have been associated with these products, mainly due to overdosage and long-term use combined with the easy oxidation of hydroquinone. In this work, an investigative study has been done to gather enough data for selecting a quantitative analytical method for quality control purposes that considers the ease of oxidation not only within the product but also during the experimental procedures. After studying the influence of pH, reversibility, sampling, and standard solution preparation on the redox reaction between hydroquinone and benzoquinone by using spectroscopic, electrophoretic, and electroanalytical measurements, a reliable, fast, and selective chronoamperometric method was achieved. The optimized method was used for the analysis of samples, previously diluted in Britton-Robinson (BR) buffer (pH 5.5) and methanol (1 : 9, v/v), by applying a potential fixed at 0.4 V. A glassy-carbon working electrode, lab-made Ag/AgCl(sat) and platinum wire as a reference electrode and auxiliary electrodes, respectively, and BR buffer (pH 5.5) as supporting electrolyte were the additional experimental conditions used. Analytical performance parameters were verified to confirm the applicability of the new method (LOD 4.22 µmol L-1 and LOQ 14.1 µmol L-1; recovery mean value of 100% with 0.22% RSD). A gel topical formulation containing 4% (w/w) hydroquinone was analyzed through the developed method for determination of dosage and oxidation traces, and a content of 3.53 ± 0.095% (w/w) was found with no indications of degradation.
Assuntos
Benzoquinonas , Hidroquinonas , Eletroquímica/métodos , Composição de MedicamentosRESUMO
Monitoring sulfur in biodiesel is of fundamental importance because even in low concentrations, it can harm the operation of the engine parts and increase the emission of toxic gases and particulate material. Hence, a simple, quick and sensitive adsorptive stripping voltammetry (AdSV) method based on a silver solid amalgam electrode (AgSAE) was developed to determine sulfur in biodiesel. The novel electrochemical method was evaluated through the linear sweep adsorptive stripping voltammetry (LSAdSV), square wave adsorptive stripping voltammetry (SWAdSV) and differential pulse adsorptive stripping voltammetry (DPAdSV) in a NH3/NH4+ buffer solution (pH 9.0), containing Na2SO3. The method was applied in biodiesel microemulsion samples under optimal conditions. To this end, a ternary phase diagram was constructed, employing three components: biodiesel/propan-1-ol/buffer solution. The microemulsion with the best response was found to be 25% NH3/NH4+ buffer (pH 9.0), 5.0% biodiesel and 70% propan-1-ol. The method reached a detection limit in the order of 10-7 mol L-1 of sulfur, and recovery values between 80% and 116%. The method was applied in the determination of sulfur in biodiesel, and the amount in the samples was found to be below the value stipulated by the regulatory agencies. The method can be a promising alternative for determining sulfur in the microemulsion of biodiesel, with the ability to provide a fast response regarding the quality of this biofuel.
Assuntos
Biocombustíveis , Prata , Eletroquímica/métodos , Eletrodos , Gases , EnxofreRESUMO
A new methodology to determine directly the fungicide boscalid (BSC) was developed and successfully applied in red grape 100% juice, peel extracts, pulp and purple grape seeds (Vitis labrusca L.) with a working carbon paste electrode (CPE) without sample preparation. Cyclic voltammetry (CV) indicated the presence of an irreversible cathodic process of BSC at -1.21 V vs. Ag|AgCl (KCl 3.0 mol L-1) in a solution of 0.100 mol L-1 HCl/acetone 70 : 30 (v/v). This behavior was also observed using Square Wave Voltammetry (SWV). The Differential Pulse Voltammetry (DPV) technique proved to be more sensitive and with higher selectivity for BSC quantification. The influence of pH on the reduction of BSC was investigated in Britton-Robinson Buffer (BRB), 0.01 mol L-1 (pH 2.00-12.00). The limit of detection (LOD) values obtained from calibration curves for different samples were as follows: 0.107 mg L-1 for deionized water; 0.146 mg L-1 for red grape 100% juice; 0.922 mg kg-1 for peel extracts; 0.818 mg kg-1 for grape pulp and 0.691 mg kg-1 for grape seeds. The corresponding Limit of Quantification (LOQ) values for the same samples were as follows: 0.358 mg L-1; 0.486 mg L-1; 2.87 mg kg-1; 2.73 mg kg-1 and 2.51 mg kg-1, respectively. In addition, the recovery rates for the different concentration levels in the investigated range varied between 97.13 and 103.4%. All tests performed with the samples did not require extraction or pre-concentration steps of BSC, resulting in a fast, simple and cheap methodology.
Assuntos
Carbono , Vitis , Compostos de Bifenilo , Eletroquímica/métodos , Eletrodos , Niacinamida/análogos & derivadosRESUMO
The use of drug delivery systems is a good technique to leave the right quantity of medicine in the patient's body in a suitable dose, because the drug application is delivered directly to the affected region. The current techniques such as HPLC and UV-Vis for the drug delivery calculation has some disadvantages, as the accuracy and the loss of the sample after characterization. With the aim of reducing the amount of material used during the characterization and have a non-destructive test with instantaneous results, the present paper shows the possibility of using electrochemical impedance spectroscopy (EIS) to have a drug delivery measurement during the release phenomena for a calcium phosphate cement (CFC) delivery system with gentamicin sulfate (GS) and lidocaine hydrochloride (LH), at a ratio of 1% and 2%, respectively. The equivalent circuit and the chemical mechanism involved during the measurements have been proposed as a tool to determine the drug delivery profile. The method has been compared with the UV-Vis technique. XRD was realized to verify conditions, before and after release. It was possible to verify the potential for using EIS as an instant technique to quantify drug delivery.
Assuntos
Sistemas de Liberação de Medicamentos , Eletroquímica/métodos , Antibacterianos/administração & dosagem , Cimentos Ósseos/química , Fosfatos de Cálcio/química , Cromatografia Líquida de Alta Pressão , Materiais Dentários , Espectroscopia Dielétrica , Liberação Controlada de Fármacos , Impedância Elétrica , Eletrólitos , Desenho de Equipamento , Gentamicinas/química , Cimentos de Ionômeros de Vidro , Humanos , Cinética , Lidocaína/química , Modelos Teóricos , Espectrofotometria , Espectrofotometria Ultravioleta , Difração de Raios XRESUMO
An original voltammetric screening method, employing glassy carbon electrode (GCE) with the differential-pulse voltammetry technique (DPV), has been developed to determine residues of the anti-parasitic agent Ronidazole (RNZ) in bovine meat. By using cyclic voltammetry (CV), it has been demonstrated that an irreversible cathodic process occurs at approximately -0.740 V (vs. Ag|AgCl, KCl 3 mol L-1) in a 0.100 mol L-1 phosphate buffer at pH 6.5 as supporting electrolyte. Furthermore, the behavior of RNZ in CV indicates the occurrence of a diffusion mass transfer process to the working electrode surface. The RNZ reduction mechanism was proposed as a 6-electron transfer, similar to Metronidazole under the same pH range. Quantification of RNZ and method validation were then carried out by DPV. The relative standard deviation (RSD) were 3.21% for intraday precision of 10 consecutive repetitions and 6.78% for interday precision after five analysis. Limits of detection and quantification were also obtained, and the values were 0.107 and 0.358 mg kg-1, respectively. The recovery percentage for three different concentrations of RNZ in the bovine meat matrix ranged between 98.1% and 100.3%. The method proved to be efficient for screening RNZ in bovine meat.
Assuntos
Eletroquímica/métodos , Análise de Alimentos/métodos , Carne Vermelha/análise , Ronidazole/análise , Animais , Carbono , Bovinos , Eletroquímica/instrumentação , Eletrodos , Análise de Alimentos/instrumentação , Contaminação de Alimentos/análise , Limite de Detecção , Reprodutibilidade dos TestesRESUMO
Arboviruses have been emerging as a significant global health problem due to the recurrent epidemics. Arboviruses require the development of new diagnostic devices due to the nonspecific clinical manifestations. Herein, we report a biosensor based on cysteine (Cys), zinc oxide nanoparticles (ZnONp), and Concanavalin A (ConA) lectin to differentiate between arboviruses infections. ConA is capable of interacting with the saccharide components of the viral capsid. In this study, we evaluated the reproducibility, sensitivity, and specificity of the sensor for the virus of Dengue type 2 (DENV2), Zika (ZIKV), Chikungunya (CHIKV), and Yellow fever (YFV). Atomic force microscopy measurements confirmed the electrode surface modification and revealed a heterogeneous topography during the biorecognition process. Cyclic voltammetry (CV) and impedance spectroscopy (EIS) were used to characterize the biosensor. The blockage of the oxidation-reduction process is related to the formation of Cys-ZnONp-ConA system on the electroactive area and its subsequent interaction with viral glycoproteins. The sensor exhibited a linear response to different concentrations of the studied arboviruses. Our study demonstrates that ConA lectin recognizes the structural glycoproteins of the DENV2, ZIKV, CHIKV, and YFV. DENV2 is the most structurally similar to ZIKV. Our results have shown that the impedimetric response correlates with the structural glycoproteins, as follow: DENV2 (18.6â¯kΩ)â¯>â¯ZIKV (14.6â¯kΩ)â¯>â¯CHIKV (6.86â¯kΩ)â¯>â¯YFV (5.98â¯kΩ). The homologous structural regions contribute to ConA-arboviruses recognition. Our results demonstrate the use of the proposed system for the development of biosensors for arboviruses infections.
Assuntos
Infecções por Arbovirus/diagnóstico , Arbovírus/metabolismo , Técnicas Biossensoriais/métodos , Concanavalina A/química , Eletroquímica/métodos , Eletrodos , Nanopartículas Metálicas/química , Infecções por Arbovirus/sangue , Infecções por Arbovirus/virologia , Arbovírus/isolamento & purificação , Febre de Chikungunya/sangue , Febre de Chikungunya/diagnóstico , Febre de Chikungunya/virologia , Vírus Chikungunya/isolamento & purificação , Vírus Chikungunya/metabolismo , Cisteína/química , Dengue/sangue , Dengue/diagnóstico , Dengue/virologia , Vírus da Dengue/isolamento & purificação , Vírus da Dengue/metabolismo , Diagnóstico Diferencial , Glucose/análise , Humanos , Manose/análise , Febre Amarela/sangue , Febre Amarela/diagnóstico , Febre Amarela/virologia , Vírus da Febre Amarela/isolamento & purificação , Vírus da Febre Amarela/metabolismo , Zika virus/isolamento & purificação , Zika virus/metabolismo , Infecção por Zika virus/sangue , Infecção por Zika virus/diagnóstico , Infecção por Zika virus/virologia , Óxido de Zinco/químicaRESUMO
Cellulose triacetate (CTAB) synthesized by cellulose extracted from sugarcane bagasse, and commercial cellulose acetate (CA) were used to produce nanofiber membranes contained bromelain by electrospinning technique. About 1.3â¯g of cellulose acetate per gram of bagasse were obtained, and both CTAB and CA was characterized by analysis of Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). The nanofiber membranes were produced by electrospinning process testing the following conditions: voltage 25â¯kV, flow rate 4â¯mL/h and distance 10â¯cm, using acetone/ dimethylformamide (DMF) (85:15â¯m/ m) to 15% cellulose triacetate (70% CAâ¯+â¯30% CTAB) or CA solutions. Scanning Electron Microscopy (SEM) was used to nanofiber membranes characterization. Bromelain was immobilized on the nanofiber membranes by crosslinking with glutaraldehyde and directly in the electrospinning step, the highest activity recovery was about 675% and in vitro controlled release tests were performed to semi-quantitatively evaluate the release of the enzyme bromelain thus demonstrating complete release process in 3 days.
Assuntos
Bromelaínas/química , Celulose/análogos & derivados , Eletroquímica/métodos , Nanofibras/química , Saccharum/química , Varredura Diferencial de Calorimetria , Celulose/química , Enzimas Imobilizadas/química , Microscopia Eletrônica de Varredura , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
O objetivo desse estudo foi sintetizar um scaffold de nanofibras (NFs) de Policaprolactona (PCL) com adição de nistatina (NYS), caracterizar e avaliar a atividade antimicrobiana. NFs foram sintetizadas pela técnica da eletrofiação, utilizando-se solução de PCL puro e PCL adicionado de NYS. Para a síntese das NFs de PCL, o polímero foi dissolvido em Dimetilformamida (DMF) e 1,1,2,2 Tetracloroetano (TCE), logo após foram adicionadas três concentrações de NYS (Grupos A, B e C). As amostras foram analisadas em Microscopia Eletrônica de Varredura (MEV), Espectroscopia por energia dispersiva (EDS), Análise de molhabilidade, Análise de Difratometria de Raios-X (DRX) e Espectroscopia de Infravermelho por Transformada de Fourier (FTIR). Após a análise em MEV foi realizada a média dos diâmetros das fibras com Software ImageJ. As atividades antimicrobianas foram avaliadas por meio dos testes de concentração inibitória mínima (CIM) e concentração microbicida mímica (CMM). As NFs de PCL com NYS (A) apresentaram diâmetro de 0,99µm ±0,29, o padrão do grupo B apresentou uma média de diâmetro de 1,3µm ±0,56 e o grupo C 1,24µm ±0,48. O DRX e o EDS comprovaram a presença de PCL e de NYS nas amostras. A CIM e a CMM comprovaram a ação fungicida e fungistática das NFs A, B e C(AU)
The aim of this study was to synthesize a scaffold of policaprolactane (PCL) nanofibers (NFs) with addition of nystatin (NYS), to characterize and evaluate the antimicrobial activity. NFs were synthesized by the electro-spinning technique, using pure PCL and NYS and PCL solutions. For the synthesis of PCL NFs, the polymer was dissolved in Dimethylformamide (DMF) and 1,1,2,2- Tetrachloroethane (TCE), after which three concentrations of NYS (Groups A, B and C) were added. The samples were analyzed in Scanning Electron Microscopy (SEM), Dispersive Energy Spectroscopy (EDS), Goniometer, X-ray Diffraction Analysis (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). After SEM analysis, the mean fiber diameter was performed with ImageJ Software. The antimicrobial activities were evaluated through the tests of minimum inhibitory concentration (MIC) and minimum microbicidal concentration (MMC).The NFs of PCL with NYS (A) had a diameter of 0.99 µm ± 0.29, the standard of group B presented a mean diameter of 1.3 µm ± 0.56 and group C 1.24 µm ± 0.48. The DRX and the EDS verified the presence of PCL and NYS in the samples. CIM and CMM proved the fungicidal and fungistatic action of NFs A, B and C(AU)
Assuntos
Candida albicans/imunologia , Eletroquímica/métodosRESUMO
In the search for new quinoid compounds endowed with potential anticancer activity, the synthesis of novel heterodimers containing the cytotoxic 7-phenylaminoisoquinolinequinone and 2-phenylaminonaphthoquinone pharmacophores, connected through methylene and ethylene spacers, is reported. The heterodimers were prepared from their respective isoquinoline and naphthoquinones and 4,4'-diaminodiphenyl alkenes. The access to the target heterodimers and their corresponding monomers was performed both through oxidative amination reactions assisted by ultrasound and CeCl3·7H2O catalysis "in water". This eco-friendly procedure was successfully extended to the one-pot synthesis of homodimers derived from the 7-phenylaminoisoquinolinequinone pharmacophore. The electrochemical properties of the monomers and dimers were determined by cyclic and square wave voltammetry. The number of electrons transferred during the oxidation process, associated to the redox potential EI1/2, was determined by controlled potential coulometry.