Determinação voltamétrica de ciclamato de sódio em produtos dietéticos empregando um eletrodo de diamante dopado com boro

The use of square-wave voltammetry in conjunction with a cathodically pre-treated diamond electrode for the analytical determination of sodium cyclamate is described. The samples were analyzed as received in a 0.5 mol L-1 H2SO4 solution in the concentration range from 5.0 × 10-5 mol L-1 to 4.1 × 10-4 mol L-1, with a detection limit of 4.8 × 10-6 mol L-1. The RSD was smaller than 1.2 % and the proposed method was applied with success in the determination of sodium cyclamate in several dietary products.

Avaliação da influência de sulfetos solúveis na complexação do cobre em águas superficiais empregando métodos voltamétricos

In this work a sulfide quantification protocol using voltammetric methods was developed to evaluate the effect of dissolved sulfides on copper complexation. On the basis of pH, sulfide release from the dissociation of specific metal sulfide complexes can be electrochemically measured and then removed (as H2S) by a N2 purge. Cathodic stripping square wave voltammetry (CSSWV) was conducted to quantify Cu sulfides complexes which dissociate at pH < 5.0 during the process of acid titration.

INVESTIGAÇÃO DO USO DE ELETRODO DE CARBONO VÍTREO MODIFICADO COM HEXACIANOFERRATO DE RUTÊNIO PARA DETECÇÃO DE PROCAÍNA

A glassy carbon electrode modified with ruthenium hexacyanoferrate (RuOHCF) was investigated as an electrocatalyst for the detection of procaine with the aim of quantification in pharmaceutical and forensic samples. The RuOHCF films were prepared by electrochemical deposition, and the parameters used in this process (concentration of RuCl3, K3Fe(CN)6, temperature, and number of cyclic voltammograms recorded in the modification step) were carefully optimized. Based on the optimal conditions achieved, the RuOHCF modified electrode allows the determination of procaine at 0.0 V with a detection limit of 11 nmol L-1using square wave voltammetry.

BIOSSENSOR ELETROQUÍMICO BASEADO NA ENZIMA TIROSINASE PARA A DETERMINAÇÃO DE FENOL EM EFLUENTES

AbstractThis work describes the development of a biosensor based on the tyrosinase enzyme (Tyr) for the determination of phenol (PHEN) in laboratory effluent samples derived from ammoniacal nitrogen analysis of the water samples from the Muquém dam in the city of Cariús, CE, using square-wave voltammetry (SWV). The electrode modification consisted of the immobilization of gold nanoparticles, multi-walled carbon nanotubes, cobalt phthalocyanine, and Tyr on a glassy carbon electrode. The electrolyte, pH, enzyme quantity, and voltammetric parameters were optimized to detect PHEN. The analytical curves presented a linear range from 4.97 × 10-6 mol L-1 to 6.10 × 10-5 mol L-1, and the detection limit (DL) and quantitation limit (QL) values were 4.81 × 10-6 mol L-1 and 4.97 × 10-6mol L-1, respectively. The repetition of measurements with the same biosensor and repetition for three other prepared biosensors exhibited a relative standard deviation (RSD) of 5.50 and 1.75%, respectively. The percentage recovery of PHEN in effluent samples varied from 86.40 to 105.04%. The stability of the biosensor was evaluated (at 21 days) with satisfactory results, showing 97.86% of the initial response. Moreover, the DL and recovery percentages agreed with the established values from CONAMA and ABNT, respectively. Thus, the electrode configuration developed seems a promising tool in the detection and quantification of PHEN in complex samples.

Comportamento eletroquímico da N-nitrosotiazolidina ácido carboxílico sobre eletrodos de ouro e mercúrio

The electrochemical behavior of N-nitrosothiazolidine carboxylic acid (NTAC) on gold and hanging mercury electrodes, using the cyclic and square wave voltammetries, was studied. Whereas NTAC suffer reduction in a single step on the mercury electrode, two peaks appears on the cyclic voltammograms on the gold electrode, one anodic peak overlaying the gold oxide process at 1.2 V and one cathodic peak at -0.41 V vs Ag/AgCl, KCl 3.0 mol L-1. The cathodic peak depends on the previous oxidation of NTAC at the electrode surface, presents irreversible and adsorption controlled characteristics and it is suitable for quantitative purposes.

Especiação de cobre e zinco em urina: importância dos metais em doenças neurodegenerativas

Metals such as copper and zinc are essential for the development and maintenance of numerous enzymatic activities, mitochondrial functions, neurotransmission, and also for memorization and learning. However, disruption in their homeostasis can cause neurodegenerative disorders such as the Alzheimer and Parkinson diseases. In this work, the speciation of copper and zinc in urine samples was carried out. To this end, free and total metal concentrations were determined by square wave anodic stripping voltammetry using a glassy carbon electrode coated with bismuth film. The digestion of the samples was performed in a microwave with the addition of oxidant reagents.

Parameter optimization of AC rectangular wave outputs for aluminum cold wire GTAW

The objective of this work was to optimize the parameter setup for GTAW of aluminum using an AC rectangular wave output and continuous feeding. A series of welds was carried-out in an industrial joint, with variation of the negative and positive current amplitude, the negative and positive duration time, the travel speed and the feeding speed. Another series was carried out to investigate the isolate effect of the negative duration time and travel speed. Bead geometry aspects were assessed, such as reinforcement, penetration, incomplete fusion and joint wall bridging. The results showed that currents at both polarities are remarkably more significant than the respective duration times. It was also shown that there is a straight relationship between welding speed and feeding speed and this relationship must be followed for obtaining sound beads. A very short positive duration time is enough for arc stability achievement and when the negative duration time is longer than 5 ms its effect on geometry appears. The possibility of optimizing the parameter selection, despite the high inter-correlation amongst them, was demonstrate through a computer program. An approach to reduce the number of variables in this process is also presented.

Eletroanálise de derivados acetaldeído com hidrazina e determinação em amostras de álcool combustível por voltametria de onda quadrada

A square wave voltammetric method is described for the determination of acetaldehyde using the derivatization reaction with hydrazine sulphate, based on the reduction of hydrazone generated as a product that exhibits a single well-defined peak at -1.19V in acetate buffer at pH 5. Calibration graphs were obtained from 1.0 x 10-6 mol L-1 to 10 x 10-6 mol L-1 of acetaldehyde, using a reaction time of 8 min and a hidrazine concentration of 0.02 mol L-1. The detection limit was 2.38 x 10-7 mol L-1. The method was applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pre-treatment.

COMPARAÇÃO DE PROCESSAMENTOS MATEMÁTICOS DE DADOS VOLTAMÉTRICOS: APLICAÇÃO NA DETERMINAÇÃO SIMULTÂNEA DE FLUOROQUINOLONAS

This paper describes a comparative study between the procedures of deconvolution and the second-order derivative of square wave voltammograms to achieve separation of the voltammetric peaks of levofloxacin (LEVO) and norfloxacin (NOR), for their simultaneous quantification in urine samples. The obtained results indicate that the use of second-derivative voltammograms coupled with carbon screen-printed electrodes is the most efficient approach for completely separating the voltammetric peaks of LEVO and NOR. In addition, this approach has produced detection limits lower than 1.0 µmol L-1 and a wide linear range for both drugs. The proposed method was successfully used to simultaneously determine LEVO and NOR in spiked human and bovine urine samples with recovery percentages close to 100% for all analyzed samples.

Chaos and Unpredictability in the Vibration of an Elasto-Plastic Beam

This contribution discusses the nonlinear dynamics of a pin-ended elasto-plastic beam with both kinematic and isotropic hardening. An iterative numerical procedure based on the operator split technique is developed in order to deal with the nonlinearities in the equations of motion. Free and forced responses for harmonic sinusoidal and square wave excitations are investigated. Numerical simulations present many interesting behaviors such as jump phenomena, sensitivity to initial conditions, chaos and transient chaos. These results indicate that there are practical problems in predicting the response of the beam even when periodic steady state response is expected.

Opioidergic orofacial antinociception induced by electroacupuncture at acupoint St36

The participation of opioids in the antinociceptive effect of electroacupuncture was evaluated in terms of nociception produced by thermal stimuli applied to the face of male Wistar rats, weighing 180-230 g. Electrical stimulation (bipolar and asymmetric square wave with 0.5 mA intensity for 20 min) of acupoint St36, located in the anterior tibial muscle 10 mm distal to the knee joint, induced antinociception in the present model, which was maintained for 150 min. Acupoint LI4, located in the junction of the first and second metacarpal bones, did not achieve antinociception at any frequency studied (5 Hz: 1.7 ± 0.1; 30 Hz: 1.8 ± 0.1; 100 Hz: 1.7 ± 0.1 vs 1.4 ± 0.2). The antinociception obtained by stimulation of acupoint St36 was only achieved when high frequency 100 Hz (3.0 ± 0.2 vs 1.0 ± 0.1) was used, and not with 5 or 30 Hz (1.2 ± 0.2 and 0.7 ± 0.1 vs 1.0 ± 0.1). The antinociceptive effect of acupuncture occurred by opioid pathway activation, since naloxone (1 and 2 mg/kg, subcutaneously) antagonized it (1.8 ± 0.2 and 1.7 ± 0.2 vs 3.0 ± 0.1).

Relation between the behaviors of P-wave and QT dispersions in elderly patients with heart failure

OBJECTIVE: To assess the relation between P-wave and QT dispersions in elderly patients with heart failure. METHODS: Forty-seven elderly patients (75.6±6 years) with stable heart failure in NYHA functional classes II or III and with ejection fractions of 37±6% underwent body surface mapping to analyze P-wave and QT dispersions. The degree of correlation between P-wave and QT dispersions was assessed, and P-wave dispersion values in patients with QT dispersion greater than and smaller than 100 ms were compared. RESULTS: The mean values of P-wave and QT dispersions were 54±14 ms and 68±27 ms, respectively. The correlation between the 2 variables was R=0.41 (p=0.04). In patients with QT dispersion values > 100 ms, P-wave dispersion was significantly greater than in those with QT dispersion values < 100 ms (58±16 vs 53±12 ms, p=0.04 ). CONCLUSION: Our results suggest that, in elderly patients with heart failure, a correlation between the values of P-wave and QT dispersions exists. These findings may have etiopathogenic, pathophysiologic, prognostic, and therapeutic implications, which should be investigated in other studies.

T-wave alternans: desempenho clínico, limitações, metodologias de análise

Reconhecer com precisão indivíduos com maior risco imediato de morte súbita cardíaca (MSC) ainda é uma questão em aberto. A natureza fortuita dos eventos cardiovasculares agudos não parece se adequar ao conhecido modelo de indução de taquicardia/fibrilação ventricular por um gatilho em sincronia a um substrato arritmogênico estático. Quanto ao mecanismo da MSC, uma instabilidade elétrica dinâmica explicaria melhor a raridade da associação simultânea de um gatilho certo a um substrato cardíaco apropriado. Diversos estudos tentaram medir essa instabilidade elétrica cardíaca (ou um equivalente válido) em uma sequência de batimentos cardíacos no ECG. Dentre os mecanismos possíveis podemos citar o prolongamento do QT, dispersão do QT, potenciais tardios, alternância de onda T ou T-wave alternans (TWA), e turbulência da frequência cardíaca. Este artigo se atém em particular ao papel da TWA no panorama atual da estratificação de risco cardíaco. Os achados sobre TWA ainda são heterogêneos, variando de um desempenho prognóstico muito bom até um quase nulo, dependendo da população clínica observada e protocolo clínico usado. Para preencher as atuais lacunas no conhecimento sobre TWA, profissionais médicos e pesquisadores devem explorar melhor as características técnicas das diversas tecnologias disponíveis para a avaliação de TWA e atentar ao fato de que os valores de TWA respondem a diversos outros fatores, além de medicamentos. Informações sobre mecanismos celulares e subcelulares da TWA estão fora do escopo deste artigo, mas são referenciados alguns dos principais trabalhos sobre este tópico, com o intuito de auxiliar no entendimento dos conceitos e fatos cobertos neste artigo.

Experiments in square lattice with a common treatment in all blocks

This paper deals with a generalization of square lattice designs, with k² treatments in blocks of k + 1 plots, the extra plot in each block receiving a standard treatment, the same for all blocks. The new design leads to lower variances for contrasts between adjusted treatment means