Square wave adsorptive cathodic stripping voltarnmetry automated by sequential injection analysis - Potentialities and limitations exemplified by the determination of methyl parathion in water samples

This paper describes the development and evaluation of a sequential injection method to automate the determination of methyl parathion by square wave adsorptive cathodic stripping voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. Accumulation and stripping steps are made in the sample medium conditioned with 40 mmol L-1 Britton-Robinson buffer (pH 10) in 0.25 mol L-1 NaNO3. The homogenized mixture is injected at a flow rate of 10 mu Ls(-1) toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode. After a suitable deposition time, the flow is stopped and the potential is scanned from -0.3 to -1.0 V versus Ag/AgCl at frequency of 250 Hz and pulse height of 25 mV The linear dynamic range is observed for methyl parathion concentrations between 0.010 and 0.50 mgL(-1), with detection and quantification limits of 2 and 7 mu gL(-1), respectively. The sampling throughput is 25 h(-1) if the in line standard addition and sample conditioning protocols are followed, but this frequency can be increased up to 61 h(-1) if the sample is conditioned off-line and quantified using an external calibration curve. The method was applied for determination of methyl parathion in spiked water samples and the accuracy was evaluated either by comparison to high performance liquid chromatography with UV detection, or by the recovery percentages. Although no evidences of statistically significant differences were observed between the expected and obtained concentrations, because of the susceptibility of the method to interference by other pesticides (e.g., parathion, dichlorvos) and natural organic matter (e.g., fulvic and humic acids), isolation of the analyte may be required when more complex sample matrices are encountered. (C) 2007 Elsevier B.V. All rights reserved.

Information Flow for ALGOL-like Languages

In this paper we present an approach to information flow analysis for a family of languages. We start with a simple imperative language. We present an information flow analysis using a flow logic. The paper contains detailed correctness proofs for this analysis. We next extend the analysis to a restricted form of Idealised Algol, a call-by-value higher-order extension of the simple imperative language (the key restriction being the lack of recursion). The paper concludes with a discussion of further extensions, including a probabilistic extension of Idealised Algol.

An electrochemical sensor for (L)-dopa based on oxovanadium-salen thin film electrode applied flow injection system

An oxovanadium-salen complex (NAP-ethylene-bis(salicylidenciminato) oxovanadium) thin film deposited on a graphite-polyurethane electrode was investigated with regard to its potential use for detection of L-dopa in flow injection system. The oxovanadium(IV)/oxovanadium(V) redox couple of the modified electrode was found to mediate the L-dopa oxidation before its use in the FIA system. Experimental parameters, such as pH of the carrier solution, flow rate, sample volume injection and probable interferents were investigated. Under the optimized FIA conditions, the amperometric signal was linearly dependent on the L-dopa concentration over the range 1.0 x 10(-1) to 1.0 x 10(-4) mol L-1 (I-anodic, mu A) = 0.01 + 0.25 [L-dopa mu mol L-1]) with a detection limit (S/N = 3) of 8.0 x 10(-7) mol L-1 and a sampling frequency of 90 h(-1) was achieved. For a concentration of 1.0 x 10(-5) mol L-1 L-dopa, the R.S.D. of nine consecutive measurements was 3.7%. (c) 2006 Elsevier B.V. All rights reserved.

Conjugação e validação de controle isotípico IgG1-FITC para uso em citometria de fluxo

Em meados da década de 50 iniciou-se o desenvolvimento da citometria de fluxo, tecnologia que permite verificar características físico-químicas de células ou partículas suspensas em meio fluido. Esta tecnologia utiliza anticorpos monoclonais marcados com fluorocromos como ferramenta de investigação em diversas análises e necessita de controles isotípicos para definição da região negativa (background). Estes controles são constituídos por imunoglobulinas de mesmo isotipo e fluorocromo dos anticorpos testes, sendo o isotiocianato de fluoresceína (FITC) o marcador fluorescente mais utilizado na conjugação de anticorpos. Os controles isotípicos têm como função definir a fluorescência inespecífica (células negativas) e as regiões fluorescentes (células positivas). No presente estudo foi selecionado anticorpo monoclonal murino (AcMm) dirigido contra antígeno eritrocitário canino, produzido no Laboratório de Anticorpos Monoclonais do Hemocentro de Botucatu, o qual reage positivamente com hemácias de cães, mas nunca com leucócitos humanos, tendo, portanto, potencial utilidade como controle negativo em citometria de fluxo. A purificação do AcMm da subclasse IgG1 foi feita por cromatografia de afinidade em Proteína-A Sepharose, e o controle da purificação realizado por eletroforese em géis de ágarose e poliacrilamida (SDS-PAGE). A imunoglobulina purificada foi conjugada ao FITC e filtrado em coluna de Sephadex G-25 para separação das proteínas marcadas e não-marcadas. O AcMm conjugado foi testado contra hemácias de cães, e o êxito da conjugação comprovado por testes de fluorescência, sendo a mediana de positividade de 94,70. Frente a leucócitos humanos a mediana de positividade foi 0,03 contra 0,50 dos reagentes comerciais. Os testes estatísticos não-paramétricos de Wilcoxon e correlação de Spearman comprovaram a eficiência e validam o controle isotípico produzido em comparação aos reagentes comerciais testados.

Study on the use of oxidant scrubbers for elimination of interferences due to nitrogen dioxide in analysis of atmospheric dimethylsulfide

Neste trabalho foi avaliado o desempenho de filtros para dióxido de nitrogênio, buscando evitar perdas durante a amostragem de sulfetos orgânicos, provocadas por oxidantes atmosféricos. Diferentes compostos e misturas foram usadas para recobrir superfícies sólidas empregadas na preparação destes filtros. Um sistema automatizado de análise em fluxo foi utilizado para comparar a eficiência de retenção de dióxido de nitrogênio pelos filtros. Entre os materiais testados na preparação dos filtros, as melhores escolhas foram papel ou lã de vidro impregnados com a mistura de sulfato de ferro (II), ácido sulfúrico e ácido pirogalico e ainda os filtros feitos de papel impregnados com trietanolamina. Os resultados obtidos em laboratório com mistura de gás padrão de dimetilsulfeto e experimentos em campo confirmaram a qualidade dos filtros e indicaram que eles podem ser utilizados para evitar a oxidação de sulfetos orgânicos durante a sua amostragem.

Laminar flow of soursop juice through concentric annuli: Friction factors and rheology

Laminar axial flow of a pseudoplastic fluid food (soursop, juice) in annular ducts has been experimentally investigated. In the first part of the manuscript, the rheological behavior of soursop juice, being essential for the annular flow analysis, was completely determined from 9.3 to 49.4 degrees Brix and temperatures from 0.4 degrees C to 68.8 degrees C, using a rotational rheometer equipped with coaxial cylinders. In order to test the adequacy of the rheology results, pressure loss data in the laminar pipe flow were collected and then experimental and theoretical friction factors were compared, showing excellent agreement, which indicated the reliability of the Power-Law model for describing the soursop juices. In the second part, pressure loss in annular regions was measured and used to estimate friction factors, which were then compared to those resulted from analytical and semi-analytical equations. The principal contributions of this article are to provide a review on the determination of friction factors-Reynolds number of pseudoplastic fluids in annuli, and also supply extensive new experimental data on the rheological properties and pressure loss of an important shear-thinning fluid food, which is of particular interest for the food engineering process design. (c) 2006 Elsevier Ltd. All rights reserved.

Optimal design of smart structures using bonded piezoelectrics for vibration control

Smart material technology has become an area of increasing interest for the development of lighter and stronger structures which are able to incorporate actuator and sensor capabilities for collocated control. In the design of actively controlled structures, the determination of the actuator locations and the controller gains, is a very important issue. For that purpose, smart material modelling, modal analysis methods, control and optimization techniques are the most important ingredients to be taken into account. The optimization problem to be solved in this context presents two interdependent aspects. The first one is related to the discrete optimal actuator location selection problem, which is solved in this paper using genetic algorithms. The second is represented by a continuous variable optimization problem, through which the control gains are determined using classical techniques. A cantilever Euler-Bernoulli beam is used to illustrate the presented methodology.

Minimization of lead and copper interferences on spectrophotometric determination of cadmium using electrolytic deposition and ion-exchange in multi-commutation flow system

A new strategy for minimization of Cu2+ and Pb2+ interferences on the spectrophotometric determination of Cd2+ by the Malachite green (MG)-iodide reaction using electrolytic deposition of interfering species and solid phase extraction of Cd2+ in flow system is proposed. The electrolytic cell comprises two coiled Pt electrodes concentrically assembled. When the sample solution is electrolyzed in a mixed solution containing 5% (v/v) HNO3, 0.1% (v/v) H2SO4 and 0.5 M NaCl, Cu2+ is deposited as Cu on the cathode, Pb2+ is deposited as PbO2 on the anode while Cd2+ is kept in solution. After electrolysis, the remaining solution passes through an AG1-X8 resin (chloride form) packed minicolumn in which Cd2+ is extracted as CdCl4/2-. Electrolyte compositions, flow rates, timing, applied current, and electrolysis time was investigated. With 60 s electrolysis time, 0.25 A applied current, Pb2+ and Cu2+ levels up to 50 and 250 mg 1-1, respectively, can be tolerated without interference. For 90 s resin loading time, a linear relationship between absorbance and analyte concentration in the 5.00-50.0 μg Cd 1-1 range (r2 = 0.9996) is obtained. A throughput of 20 samples per h is achieved, corresponding to about 0.7 mg MG and 500 mg KI and 5 ml sample consumed per determination. The detection limit is 0.23 μg Cd 1-1. The accuracy was checked for cadmium determination in standard reference materials, vegetables and tap water. Results were in agreement with certified values of standard reference materials and with those obtained by graphite furnace atomic absorption spectrometry at 95% confidence level. The R.S.D. for plant digests and water containing 13.0 μg Cd 1-1 was 3.85% (n = 12). The recoveries of analyte spikes added to the water and vegetable samples ranged from 94 to 104%. (C) 2000 Elsevier Science B.V.

AI automates substation control

An overview is given on the possibility of controlling the status of circuit breakers (CB) in a substations with the use of a knowledge base that relates some of the operation magnitudes, mixing status variables with time variables and fuzzy sets. It is shown that even when all the magnitudes to be controlled cannot be included in the analysis, it is possible to control the desired status while supervising some important magnitudes as the voltage, power factor, and harmonic distortion, as well as the present status.

Spectrophotometric flow-injection determination of sulphite in white wines involving gas diffusion through a concentric tubular membrane

A flow-injection system is proposed for the spectrophotometric determination of sulphite in white wines. The method involves analyte conversion to SO2, gas diffusion through a Teflon® semi-permeable membrane, collection into an alkaline stream (pH 8), reaction with Malachite green (MG) and monitoring at 620 nm. With a concentric tubular membrane, the system design was simplified. Influence of reagent concentrations, pH of donor and acceptor streams, temperature, timing, surfactant addition and presence of potential interfering species of the wine matrix were investigated. A pronounced (ca. 100%) enhancement in sensitivity was noted by adding cetylpyridinium chloride (CPC). The proposed system is robust and baseline drift is not observed during 4 h operating periods. Only 400 μL of sample and 0.32 mg MG are required per determination. The system handles 30 samples per hour, yielding precise results (r.s.d. < 0.015 for 1.0 - 20.0 mg L-1 SO2) in agreement with those obtained by an alternative procedure.

Analysis of a sub-optimal scheme of drug dosage in the AIDS treatment

Here the results for CD4+T cells count and the viral load obtained from HIV sero-positive patients are compared with results from numerical simulations by computer. Also, the standard scheme of administration of drugs anti HIV (HAART schemes) which uses constant doses is compared with an alternative sub-optimal teatment scheme which uses variable drug dosage according to the evolution of a quantitative measure of the side effects. The quantitative analysis done here shows that it is possible to obtain, using the alternative scheme, the same performance of actual data but using variable dosage and having fewer side effects. Optimal control theory is used to solve and also to provide a prognosis related to the strategies for control of viraemia.

A multicommuted flow-based system for hydrogen peroxide determination by chemiluminescence detection using a photodiode

A simple, rapid, and automated assay for hydrogen peroxide in pharmaceutical samples was developed by combining the multicommutation system with a chemiluminescence (CL) detector. The detection was performed using a spiral flow-cell reactor made from polyethylene tubing that was positioned in front of a photodiode. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. The chemiluminescence was based on the reaction of luminol with hydrogen peroxide catalyzed by hexacyanoferrate(III). The feasibility of the flow system was ascertained by analyzing a set of pharmaceutical samples. A linear response within the range of 2.2-210 μmol l-1 H2O2 with a LD of 1.8 μmol l-1 H2O2 and coefficient of variations smaller than 0.8% for 1.0×10-5 mol l-1 and 6.8×10-5 mol l-1 hydrogen peroxide solutions (n=10) were obtained. Reagents consumption of 90 μg of luminol and 0.7 mg of hexacyanoferrate(III) per determination and sampling rate of 200 samples per hour were also achieved. Copyright © Taylor & Francis Group, LLC.

Structural real time control using fluid magnetorheologic damper

In the last decades there was a great development in the study of control systems to attenuate the harmful effect of natural events in great structures, as buildings and bridges. Magnetorheological fluid (MR), that is an intelligent material, has been considered in many proposals of project for these controllers. This work presents the controller design using feedback of states through LMI (Linear Matrix Inequalities) approach. The experimental test were carried out in a structure with two degrees of freedom with a connected shock absorber MR. Experimental tests were realized in order to specify the features of this semi-active controller. In this case, there exist states that are not measurable, so the feedback of the states involves the project of an estimator. The coupling of the MR damper causes a variation in dynamics properties, so an identification methods, based on experimental input/output signal was used to compare with the numerical application. The identification method of Prediction Error Methods - (PEM) was used to find the physical characteristics of the system through realization in modal space of states. This proposal allows the project of a semi-active control, where the main characteristic is the possibility of the variation of the damping coefficient.

A simple and environmentally friendly reflectometric method for the rapid quantitative analysis of captopril in pharmaceutical formulations

This paper describes a simple, environmentally friendly and rapid quantitative spot test procedure for the determination of captopril (CPT) in bulk drug and in pharmaceutical formulations by using diffuse reflectance spectroscopy. The proposed method is based on the reflectance measurements of the orange compound (λ max 490 nm) produced by the spot test reaction between CPT and p-chloranil (CL). Under optimal conditions, calibration curves were obtained for CPT by plotting the optical density of the reflectance signal (A R) vs. the log of the mol L -1 concentration, from 6.91×10 -3 to 1.17×10 -1, with a good coefficient of determination (R 2 = 0.9992). The common excipients used as additives in pharmaceuticals do not interfere in the proposed method. The method was applied to determine CPT in commercial pharmaceutical formulations. The results obtained by the proposed method are compared favorably with those obtained by an official procedure at 95% confidence level. The method validation results showed that the sensitivity and selectivity of the methods were adequated for drug monitoring in industrial quality control laboratories. © 2011 Moment Publication.

Fabricação de microcanais para integração de uma língua eletrônica em um sistema lab-on-a-chip

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)