Um procedimento simples e de baixo custo, baseado na elevada diferença de solubilidade de cloreto de sódio em etanol e em água, é proposto para a estimativa do teor de água em etanol combustível. A concentração iônica de soluções saturadas com o sal é monitorada por medidas de condutividade com resposta linear até 16% de água em meio alcoólico e limite de detecção de 0,05% (v/v). O procedimento é preciso (coeficiente de variação de 0,6%, n = 10) e exato (resultados concordantes com os obtidos por titulação amperométrica de Karl Fischer com 95% de confiança). Um dispositivo eletrônico que explora o mesmo princípio foi proposto para monitoramento in situ de etanol combustível visando à detecção rápida de não conformidades. O dispositivo pode ser operado por não especialistas, gerando uma resposta binária indicada por LEDs coloridos e foi usado com sucesso na classificação de amostras comerciais adulteradas com diferentes quantidades de água.

A simple and inexpensive procedure, based on the high difference in solubility of sodium chloride in ethanol and water, is proposed to estimate the water content in ethanol fuel. The ionic concentration of solutions saturated with the salt is monitored by conductometric measurements with a linear response up to 16% water in an alcoholic medium and a limit of detection of 0.05% (v/v). The procedure is precise (coefficient of variation of 0.6%, n = 10) and accurate (results in agreement with those obtained by Karl Fischer amperometric titration at the 95% confidence level). An indicating electronic device exploiting the same principle was proposed for in situ monitoring of ethanol fuel samples aiming at the fast detection of unconformities. The device can be operated by nonexperts, generating a binary response indicated by coloured LEDs, and it successfully classified commercial samples spiked with different amounts of water.

The potentialities and applications of the Multiple Pulse Amperometric detection (MPA) coupled with Flow Injection Analysis (FIA) are evaluated. Important aspects as cleaning and activation of electrode surface, indirect and simultaneous analysis of electroactive compounds and the use of the internal standard method for quantifications utilizing FIA-MPA are presented. The main parameters concerning the detection of electroactive analytes by multiple pulse amperometric detection in flowing solutions were also discussed. In addition, aspects such as flow rate, sample volume, application time of the potential pulses and instrumentation necessary for implementing of the method were also addressed.

The supply of drinking water in the Metropolitan Area of São Paulo City has been a great and serious challenge in the latest years. This work demonstrates the viability of the evaluation of the degree of contamination of the water reservoirs using analytical procedures, which allow the analysis of several compounds at relatively low cost: stripping square wave voltammetry (SSWV) and capillary zone electrophoresis with contactless conductivity detection (CZE-CCD). The results of ionic composition indicated significant contamination of the Guarapiranga water system by human activities on the reservoir banks. In fact, the Guavirutuba and Itupu streams presented high concentrations of phosphate and ammonium ions. This can be directly related to misuse and unruled occupation of the soil and precarious sanitary infrastructure.

In this work a simple and versatile procedure is described for treating water samples using small polypropylene (PP) vials (4 mL) for determining heavy metals by square wave voltammetry (SWV). This procedure involves treatment with nitric acid (0.2 mol L-1) and boiling in a water-bath (~ 100 ºC). This process is completed after one hour and allows the pretreatment of several samples simultaneously. The accuracy was estimated using addition/recovery studies and certified water sample analysis, yielding an agreement near to 100%.

Este trabalho apresenta a determinação de diversos analitos em água de coco por eletroforese capilar com detecção condutométrica sem contato (CCD). Foram analisadas 5 diferentes amostras: duas não processadas (naturais) e três industrialmente processadas (comerciais). As amostras foram injetadas sem tratamento prévio e apenas uma simples diluição foi necessária. A técnica foi aplicada para quantificação de 12 analitos: cloreto, sulfato, fosfato, malato, ascorbato, potássio, sódio, cálcio, magnésio, frutose, glicose e sacarose, sendo que seus respectivos limites de detecção (LOD) são: 0,09; 0,12; 0,50; 0,97; 1,2; 0,05; 0,17; 0,12; 0,08; 5,4; 7,4 e 8,9 mg L-1. Para realizar estas análises, foram utilizados quatro tampões de corrida diferentes.

This work presents the determination of several analytes in coconut water by using capillary electrophoresis with contactless conductivity detection (CCD). It was analyzed 5 different samples: two unprocessed (natural) coconut water and three processed (commercial) ones. The samples were injected without pretreatment and only a simple dilution was necessary. The technique was applied to quantify 12 analytes: chloride, sulfate, phosphate, malate, ascorbate, potassium, sodium, calcium, magnesium, fructose, glucose, and sucrose with limit of detection (LOD) of 0.09, 0.12, 0.50, 0.97, 1.2, 0.05, 0.17, 0.12, 0.08, 5.4, 7.4, and 8.9 mg L-1, respectively. These analysis were done utilizing four different running buffers.

O controle do conteúdo de íons inorgânicos em combustíveis veiculares tem uma importante função na manutenção do motor. Um método novo e versátil para análise rápida de íons em etanol é apresentado. Eletroforese capilar foi utilizada para quantificar cátions (sódio, potássio, cálcio, magnésio e amônio) e ânions (sulfato, cloreto e nitrato). A injeção direta da amostra no capilar apresentou falta de repetibilidade nos resultados. A evaporação prévia do etanol, seguida pela resuspensão do material residual, levou a resultados confiáveis. Os limites de detecção para os oito íons estiveram na faixa de 0,06 a 0,18 mg L-1. Limites de detecção inferiores podem ser obtidos com o aumento do tempo de injeção e/ou da pressão de injeção.

The control of the content of inorganic ions in vehicular fuels plays an important role in the engine maintenance. A novel and versatile methodology to carry out rapid analysis of ions in ethanol is presented. Capillary electrophoresis was used to quantify cations (sodium, potassium, calcium, magnesium, and ammonium) and anions (sulfate, chloride, and nitrate). The injection of the sample directly in the capillary shows some lack of repeatability of the results. The prior evaporation of the ethanol, followed by a re-suspension of the residual material, leads to reliable results. The detection limits of the eight ions range between 0.06 and 0.18 mg L-1. Lower detection limits could be attained by increasing the injection time and/or the injection pressure.

A digital multimeter (~U$ 240.00 on the national market) connected to a microcomputer by a RS-232 serial interface is proposed for data acquisition in equipment with analog output. Data are measured at the rate of 2 points per second and stored in text files by the software that accompanies the device, running in a Windows environment. The performance of the multimeter was verified by monitoring the transient signals generated in flow injection systems associated with fluorimetric, spectrophotometric and flame photometric detection. In addition, the performance of the proposed device was similar to that attained by employing an interface card with a 12-bit analog-to-digital converter for acquisition of the signals generated by a capillary electrophoresis equipment with oscillometric detection.

This paper presents a new way for the construction of silver electrodes utilizing recordable CDs. The new electrodes were explored for the quantification of chloride (by potentiometry/FIA), cyanide (by amperometry/FIA) and for lead analysis (by square wave voltammetry). For the flowing measurements, a digital multimeter, connected to a microcomputer (via RS 232 interface) was used to collect directly the potential signal (for Cl- measurements) or to take the output signal from a potentiostat (for CN- measurements). The square wave voltammetry analysis was performed in a commercial instrument. The results shown good performance of the new electrodes and the detection limit (s/n = 3) attained for these three analytes were: 0.2, 50, and 200 µg L-1 for Pb2+, Cl-, and CN- respectively.

Aquarium air pumps are proposed and evaluated as pneumatic liquid propulsion devices for flow injection and continuos flow analysis (FIA and CFA) systems. This kind of pump is widely available at a very low cost and it can sustain a pressure around of 4 psi (0.28 bar) indefinitely. By applying this air pressure onto a solution contained in a reservoir flask, it is possible to reach flow rates of up to 12.5 mL min-1 for circuits comprising reactors, made from 0.8 i.d. tubing with a length of 100 cm. The precise adjustment of flow rate below the maximum one can be made with a simplified needle valve or inserting in series a short length of capillary tube. The absence of flow pulsation is a definite advantage in comparison with peristaltic pumps, especially when amperometric detection is elected, as confirmed experimentally in FIA and CF applications.

The ability of enzymes to function in aquo-restricted media (commonly reported as non-aqueous media) has greatly enlarged the applications in numerous fields. The development of biosensors was also benefited with this area, expanding their applications toward many previously inaccessible analytes, enlarging significantly the scope of applications. In this review, some basic factors that influence biocatalytical reactions in aquo-restricted media is discussed. Attention is focused on the development, advantages and analytical applications of biosensors in non-aqueous media. Recent examples and relevant applications of their use are presented.

A review dealing with the use of screen-printing technology to manufacture disposable electrodes is presented, covering in details virtually all the publications in the area up to early 1997 and including 206 references. The elements and different strategies on constructing modified electrodes are highlighted. Commercial and Home-made ink recipes are discussed. Microelectrode arrays, built by the combination of photostructuring and screen-printing technologies to the mass production of advanced disposable sensors, are also discussed. Future research trends are predicted.