Development and characterization of modified electrodes with conducting polymer materials for electroanalytical detection of pesticides.

O estudo de polímeros condutores desperta um enorme interesse científico e tecnológico devido às diversas aplicações possíveis para esses materiais, como o desenvolvimento de dispositivos eletro-eletrônicos e sensores. Através de processos de dopagem esses polímeros tornam-se eletroativos, possibilitando por meio de técnicas eletroquímicas a determinação de diversas substâncias. Na agropecuária, a utilização intensiva e crescente de produtos químicos como pesticidas e fertilizantes, tem provocado diversas contaminações e agressões, despertando interesse na utilização de sensores para o monitoramento dessas substâncias em tempo real. Os eletrodos modificados com polímeros condutores têm-se apresentado como uma alternativa devido a algumas peculiaridades como alta estabilidade física e química e excelentes possibilidades analíticas devido à versatilidade da polimerização eletroquímica. Este trabalho teve como objetivo o desenvolvimento de novos materiais de eletrodos modificados com polímeros condutores para a determinação eletroanalítica de pesticidas. Os pesticidas estudados foram os herbicidas 2,4-D, bentazon, glifosato, paraquat e o inseticida paration metílico. Foram realizadas medidas voltamétricas e de impedância com eletrodos de carbono vítreo, pasta de carbono e eletrodos modificados com polianilina e polipirrol, visando a obtenção de sensores para a detecção destes pesticidas. Estudos de interação dos pesticidas com os polímeros foram realizados utilizando-se a técnica de espectrofotometria de UV-visível para a determinação da concentração dos pesticidas em estudos cinéticos. Também utilizou-se a espectroscopia de impedância eletroquímica para auxiliar no entendimento das interações entre os pesticidas e os polímeros condutores. Adicionalmente foi aplicada uma metodologia de análise de fluxo descontínuo (BIA), utilizada com sucesso na determinação de metais, para a determinação de pesticidas. Os resultados mostraram uma seletividade nas interações entre os polímeros condutores e os pesticidas. Por meio da resposta voltamétrica dos polímeros condutores, os eletrodos de pasta modificados com polianilina e polipirrol mostraram-se hábeis na detecção dos pesticidas não eletroativos como o 2,4-D, o bentazon e o glifosato, bem como na determinação do paraquat. Estes resultados atribuem aos eletrodos modificados desenvolvidos neste trabalho a característica de sensores de diagnóstico da presença destes pesticidas em solução. A metodologia de BIA na determinação de pesticidas, apresentou inúmeras vantagens do ponto de vista analítico, como a não renovação da superfície de eletrodo, micro-volumes de injeção de amostra, dezenas de análise sem troca do eletrólito suporte, tempos de análise inferiores a um segundo bem como a possibilidade de utilização de dispositivo portátil para análises em campo.Studies of conducting polymers have great technological and scientific interest due to many possibilities of applications like the development of electronic devices and sensors. By means of a doping process these polymers became electroactives, allowing the determination of substances that specifically interact with the polymers. In agriculture the intensive and constant use of chemical substances as pesticides and fertilizers are causing several environmental contamination and the development of sensors for real time analysis has been a research field of intense interest. Electrodes modified with conducting polymers have several interesting characteristics as their high physical and chemical stability and excellent analytical possibilities, due to the versatility of the electrochemical polymerization. The objective of the present work was the development of electrode materials modified with conducting polymers for the electroanalytical determination of pesticides. The pesticides studied were the herbicide 2,4-D, bentazon, gliphosate and paraquat and the insecticide methylparathion. Voltammetric measurements were performed on glassy carbon and carbon paste electrodes modified with polianiline and polipirrol to obtain a procedure for the pesticides measurement. Studies of interaction between the pesticides and the polymers were performed using UV-visible spectrophotometry for pesticide concentration determination kinetic sorption experiments and the electrochemical impedance technique was also used to evaluate such sorption processes. Batch Injection Analysis (BIA), a technique successfully used for the analysis of metals, was also tested for the determination of the herbicide paraquat. Results obtained from the kinetic studies and the voltammetric and impedance experiments showed some selectivity for the interaction of the pesticide with the two polymers. By means of the voltammetric response of the polymers, the carbon paste electrode modified with polianiline showed to be very suitable for the detection of the herbicide 2,4-D, bentazon and gliphosate, but not for paraquat and methilparathion. On the other hand the carbon paste electrode modified with polipirrol detect only the gliphosate and paraquat. The results shows that the detection of the paraquat and the gliphosate by the polipirrol are not influenced by protonation, whereas the detection of the 2,4-D, bentazon and gliphosate by the polianiline are due to sorption and consequent doping of the polymer by the pesticides, which have acidic behavior. The BIA technique used for the detection of the pesticide paraquat, showed a good sensitivity and could be used in the future for the analysis of such substances with many advantages when compared with conventional electroanalytical procedures

Development and characterization of modified electrodes with conducting polymer materials for electroanalytical detection of pesticides.

O estudo de polímeros condutores desperta um enorme interesse científico e tecnológico devido às diversas aplicações possíveis para esses materiais, como o desenvolvimento de dispositivos eletro-eletrônicos e sensores. Através de processos de dopagem esses polímeros tornam-se eletroativos, possibilitando por meio de técnicas eletroquímicas a determinação de diversas substâncias. Na agropecuária, a utilização intensiva e crescente de produtos químicos como pesticidas e fertilizantes, tem provocado diversas contaminações e agressões, despertando interesse na utilização de sensores para o monitoramento dessas substâncias em tempo real. Os eletrodos modificados com polímeros condutores têm-se apresentado como uma alternativa devido a algumas peculiaridades como alta estabilidade física e química e excelentes possibilidades analíticas devido à versatilidade da polimerização eletroquímica. Este trabalho teve como objetivo o desenvolvimento de novos materiais de eletrodos modificados com polímeros condutores para a determinação eletroanalítica de pesticidas. Os pesticidas estudados foram os herbicidas 2,4-D, bentazon, glifosato, paraquat e o inseticida paration metílico. Foram realizadas medidas voltamétricas e de impedância com eletrodos de carbono vítreo, pasta de carbono e eletrodos modificados com polianilina e polipirrol, visando a obtenção de sensores para a detecção destes pesticidas. Estudos de interação dos pesticidas com os polímeros foram realizados utilizando-se a técnica de espectrofotometria de UV-visível para a determinação da concentração dos pesticidas em estudos cinéticos. Também utilizou-se a espectroscopia de impedância eletroquímica para auxiliar no entendimento das interações entre os pesticidas e os polímeros condutores. Adicionalmente foi aplicada uma metodologia de análise de fluxo descontínuo (BIA), utilizada com sucesso na determinação de metais, para a determinação de pesticidas. Os resultados mostraram uma seletividade nas interações entre os polímeros condutores e os pesticidas. Por meio da resposta voltamétrica dos polímeros condutores, os eletrodos de pasta modificados com polianilina e polipirrol mostraram-se hábeis na detecção dos pesticidas não eletroativos como o 2,4-D, o bentazon e o glifosato, bem como na determinação do paraquat. Estes resultados atribuem aos eletrodos modificados desenvolvidos neste trabalho a característica de sensores de diagnóstico da presença destes pesticidas em solução. A metodologia de BIA na determinação de pesticidas, apresentou inúmeras vantagens do ponto de vista analítico, como a não renovação da superfície de eletrodo, micro-volumes de injeção de amostra, dezenas de análise sem troca do eletrólito suporte, tempos de análise inferiores a um segundo bem como a possibilidade de utilização de dispositivo portátil para análises em campo.Studies of conducting polymers have great technological and scientific interest due to many possibilities of applications like the development of electronic devices and sensors. By means of a doping process these polymers became electroactives, allowing the determination of substances that specifically interact with the polymers. In agriculture the intensive and constant use of chemical substances as pesticides and fertilizers are causing several environmental contamination and the development of sensors for real time analysis has been a research field of intense interest. Electrodes modified with conducting polymers have several interesting characteristics as their high physical and chemical stability and excellent analytical possibilities, due to the versatility of the electrochemical polymerization. The objective of the present work was the development of electrode materials modified with conducting polymers for the electroanalytical determination of pesticides. The pesticides studied were the herbicide 2,4-D, bentazon, gliphosate and paraquat and the insecticide methylparathion. Voltammetric measurements were performed on glassy carbon and carbon paste electrodes modified with polianiline and polipirrol to obtain a procedure for the pesticides measurement. Studies of interaction between the pesticides and the polymers were performed using UV-visible spectrophotometry for pesticide concentration determination kinetic sorption experiments and the electrochemical impedance technique was also used to evaluate such sorption processes. Batch Injection Analysis (BIA), a technique successfully used for the analysis of metals, was also tested for the determination of the herbicide paraquat. Results obtained from the kinetic studies and the voltammetric and impedance experiments showed some selectivity for the interaction of the pesticide with the two polymers. By means of the voltammetric response of the polymers, the carbon paste electrode modified with polianiline showed to be very suitable for the detection of the herbicide 2,4-D, bentazon and gliphosate, but not for paraquat and methilparathion. On the other hand the carbon paste electrode modified with polipirrol detect only the gliphosate and paraquat. The results shows that the detection of the paraquat and the gliphosate by the polipirrol are not influenced by protonation, whereas the detection of the 2,4-D, bentazon and gliphosate by the polianiline are due to sorption and consequent doping of the polymer by the pesticides, which have acidic behavior. The BIA technique used for the detection of the pesticide paraquat, showed a good sensitivity and could be used in the future for the analysis of such substances with many advantages when compared with conventional electroanalytical procedures

Electroanalytical Determination of Fenthion in Passiflora alata Tincture Samples

In this work a direct, simple, fast and sensitive method to determine Fenthion was developed using a Boron-Doped Diamond Electrode and Square Wave Voltammetry. The method was applied into Passiflora alata herbal medicinal tinctures derivate from passion fruits. None previous treatment such as derivation or pre-concentration of the analyte was done. Cyclic Voltammetry results showed well defined irreversible oxidation peaks at around 1.27 V into the pH range of 2.0 to 8.0. Square Wave Voltammetry was used to analytical determination and the analysis parameters, such as frequency, amplitude and pH from support electrolyte were optimized. A calibration curve was obtained, and it was observed a sensitivity of 0.38 A/mol L-1 and linearity of 0.995. The limits of detection and quantification were 8.0x10-8 mol L-1 (21 mg L-1) and 2.5x10-7 mol L-1 (70 mg L-1), respectively. Recovery studies were applied using Passiflora alata samples fortified with Fenthion in concentrations of 2.5 µmol L-1and 4.0 µmol L-1, followed by the standard addition of the pesticide aliquots. It was observed that the complex matrix does not interferes in the method. The recovery results were about 98.4 and 112.0%, reinforcing that the method is suitable to determine the analyte in target complexes samples, such as Herbal Medicinal Plants. DOI: http://dx.doi.org/10.17807/orbital.v10i2.1077 </p

Persistence Length, Mass Fractal, and Branching in the Aggregating of Vinyltriethoxysilane-Derived Organic/Silica Hybrids

The time evolution of the local chain persistence determined by small-angle X-ray scattering (SAXS) in the aggregation kinetics of vinyltriethoxysilane(VTES)-derived organic/silica hybrids has been analyzed by the classical Sharp and Bloomfield (SB) model, by a mass-fractal Unified Function (UF) with an arbitrary mass-fractal dimension D, and by a modified branching Sharp-Bloomfield (BSB) model incorporating a branching probability parameter. The SB function describes well the SAXS data, but it is restricted to stages close to the appearance of a plateau in the Kratky plots. The UF and BSB models describe well the SAXS data up to the plateau and afterward when maxima rise in the Kratky plots, the maxima increasing in intensity and shifting toward the low-q with time. The UF approach does not apply to the data at the early stages of aggregation, when D is apparently not so different from the exponent similar to 1 of the rod-like power-law regime at high-q. The values of the persistence length l(p), the contour length L, the gyration radius R-g, and the mass density per chain length M/L as determined from the different approaches were used to probe the applicability of the methods.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Temperature Effect on the Structure and Formation Kinetics of Vinyltriethoxysilane-Derived Organic/Silica Hybrids

The structure and formation kinetics of organic/silica hybrid species prepared from acid hydrolysis of vinyltriethoxisilane has been studied in situ by small-angle X-ray scattering (SAXS) at 298, 318, and 333 K in a strongly basic step of the process. The evolution of the SAXS intensity is compatible with the formation of linear chains which grow, coil, and branch to form polymeric macromolecules in solution. The SAXS data were analyzed by the scattering from a persistent chain model for polymeric macromolecules in solution using a modified branching Sharp and Bloomfield global function, which incorporates a branching probability typical of randomly and nonrandomly branched polycondensates, and in a particular case, it is also valid for polydisperse coils of linear chains. Growth of linear chains and coiling dominate the process up to the formation of likely monodisperse Gaussian coils or polydisperse coils of linear chains. The link probability to form a branching point is increased with time to form nonrandomly branched polycondensates in solution. The kinetics of the process is accelerated with temperature, but all the curves formed by the time evolution of the structural parameters in all temperatures can correspondingly be matched on a unique curve by using an appropriate time scaling factor. The activation energy of the process was evaluated as Delta E = 21 +/- 1 kJ/mol. The characteristics of the kinetics are in favor of a complex overall mechanism controlled by both condensation reactions and dynamical forces driven by interfacial energy up to the final structure development of the hybrids.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Geoeconomic variations in epidemiology, ventilation management, and outcomes in invasively ventilated intensive care unit patients without acute respiratory distress syndrome: a pooled analysis of four observational studies

Background: Geoeconomic variations in epidemiology, the practice of ventilation, and outcome in invasively ventilated intensive care unit (ICU) patients without acute respiratory distress syndrome (ARDS) remain unexplored. In this analysis we aim to address these gaps using individual patient data of four large observational studies. Methods: In this pooled analysis we harmonised individual patient data from the ERICC, LUNG SAFE, PRoVENT, and PRoVENT-iMiC prospective observational studies, which were conducted from June, 2011, to December, 2018, in 534 ICUs in 54 countries. We used the 2016 World Bank classification to define two geoeconomic regions: middle-income countries (MICs) and high-income countries (HICs). ARDS was defined according to the Berlin criteria. Descriptive statistics were used to compare patients in MICs versus HICs. The primary outcome was the use of low tidal volume ventilation (LTVV) for the first 3 days of mechanical ventilation. Secondary outcomes were key ventilation parameters (tidal volume size, positive end-expiratory pressure, fraction of inspired oxygen, peak pressure, plateau pressure, driving pressure, and respiratory rate), patient characteristics, the risk for and actual development of acute respiratory distress syndrome after the first day of ventilation, duration of ventilation, ICU length of stay, and ICU mortality. Findings: Of the 7608 patients included in the original studies, this analysis included 3852 patients without ARDS, of whom 2345 were from MICs and 1507 were from HICs. Patients in MICs were younger, shorter and with a slightly lower body-mass index, more often had diabetes and active cancer, but less often chronic obstructive pulmonary disease and heart failure than patients from HICs. Sequential organ failure assessment scores were similar in MICs and HICs. Use of LTVV in MICs and HICs was comparable (42·4% vs 44·2%; absolute difference -1·69 [-9·58 to 6·11] p=0·67; data available in 3174 [82%] of 3852 patients). The median applied positive end expiratory pressure was lower in MICs than in HICs (5 [IQR 5-8] vs 6 [5-8] cm H2O; p=0·0011). ICU mortality was higher in MICs than in HICs (30·5% vs 19·9%; p=0·0004; adjusted effect 16·41% [95% CI 9·52-23·52]; p&lt;0·0001) and was inversely associated with gross domestic product (adjusted odds ratio for a US$10 000 increase per capita 0·80 [95% CI 0·75-0·86]; p&lt;0·0001). Interpretation: Despite similar disease severity and ventilation management, ICU mortality in patients without ARDS is higher in MICs than in HICs, with a strong association with country-level economic status

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P &lt; 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)