Sample preparation is commonly considered a key step to achieve selective, sensitive, and reliable chemical analyses, particularly those involving complex matrices. Although the application of electric fields to improve the speed and efficiency of sample preparation methods has been proven, this approach is still considered to be state-of-the-art; hence, further development is necessary to improve future applications. This review describes the fundamentals, advances, applications, and perspectives of using electric fields to enhance sample preparation techniques such as liquid-liquid and solid-liquid extractions in conventional and microscale devices.

Neste trabalho é descrita a construção de um microssistema em silício para retenção de íons cobre(II). Processo fotolitográfico convencional foi empregado para transferir o padrão de microcanais para o substrato de silício. Utilizando corrosão por íons reativos (RIE) com plasma de SF6, foram produzidos canais de 50 µm de largura e 10 µm de profundidade. Os canais foram selados com vidro de borossilicato utilizando-se a técnica de soldagem anódica. Para promover a retenção dos íons cobre(II), a superfície dos canais foi modificada através de reação de silanização com N-(beta-aminoetil)-gama-aminopropiltrimetóxisilano. Os íons cobre(II) foram detectados amperometricamente na saída do canal utilizando-se um eletrodo de ouro. Os íons cobre(II) foram eluídos com HCl 50 mmol L-1 em um sistema micro-FIA com fluxo de 100 µL min-1. A reprodutibilidade em termos de área e altura do pico foram de 4,6 % e 10 %, respectivamente, para três injeções consecutivas de 600 µL de solução de cobre(II) 10 µmol L-1.

This work describes the construction of a silicon microchip for retention of copper(II) metal ions. Conventional photolithographic process was applied to transfer the generated pattern to silicon wafers. Using Reactive Ion Etching (RIE), SF6 based, channels 50 µm wide and 10 µm deep were produced. The channels were sealed with borosilicate glass using anodic bonding process. The surface of the channels were modified with N-(beta-aminoethyl)-gamma-aminopropyltrimetoxysilane through a silanization reaction to promote the adsorption of copper(II) ions. An amperometric detector was placed at the microchip outlet and copper(II) ions were detected by a gold electrode at 0 V (against Ag/AgCl(KCl sat.) reference electrode). Copper(II) ions were retained and eluted with HCl 50 µmol L-1 in a micro-flow system at a flow rate about 100 µL min-1. Reproducibility in the peak area and height were about 4.6 % and 10 %, respectively, for three consecutive injections of 600 µL of 10 µmol L-1 copper(II) sample.

This article describes a novel approach to the separation of fatty acids ranging from 8 to 20 carbons using capillary electrophoresis with contactless conductivity detection. Complete separation of nine linear chain fatty acids (from C8:0 to C20:0) was achieved in 15 min under normal polarity operation. Limits of detection ranged from 35 to 319 µmol L-1 for C20:0 to C8:0, respectively. The optimized running electrolyte composition was 5.0 mmol L-1 phosphate buffer at pH 7, 4.0 mmol L-1 dimethyl-b-cyclodextrin, 2.0 mmol L-1 trimethyl-b-cyclodextrin, acetonitrile 50% (v/v), and methanol 20% (v/v). The applicability of the separation system was demonstrated by the analysis of coconut vegetable oil.

Um dos usos mais comuns da eletroforese capilar com detecção condutométrica é a análise de vários tipos de amostras contendo metais alcalinos e alcalinos terrosos. No entanto, a alta concentração de sódio, a qual é uma ocorrência bastante comum, pode causar perda de resolução de alguns picos. Neste trabalho, as condições e o eletrólito de corrida conveniente para análises de soro e fluído para hemodiálise são apresentados. A idéia básica é deslocar os picos de Ca2+ e Mg2+ pela redução de suas mobilidades pela adição de lactato e metanol ao eletrólito de corrida. Limites de detecção da ordem de 0,5 a 1,0 mmol L-1 e razão molar Na+/Ca2+ da ordem de 1000 foram obtidos. Estas condições excedem as necessidades da aplicação pretendida.

One of the most common uses of capillary electrophoresis with conductometric detection is the analysis of different samples containing alkaline and alkaline earth metals. However, the high sodium content, which is a very common occurrence, may cause loss of resolution of some peaks. In this work, the conditions and a running buffer suitable for serum and hemodialysis fluid analyses are presented. The approach basically consists in the reduction of mobilities of Ca2+ and Mg2+ by addition of methanol and lactate in the running buffer. Limits of detection in the range from 0.5 to 1.0 mmol L-1 with molar Na+/Ca2+ ratios as high as 1000 were obtained, which are conditions that exceed the requirements of the proposed determination.

This technical note describes a new and simple electronic circuit for driving solenoid valves. The circuit is based on a single integrated circuit DRV103, which is able to drive resistive or inductive loads up to 1.5 A. Switching of 12-V loads can be controlled by TTLlevel signals in two distinct steps. Initially, 12 V is applied during 110 ms, followed by 4.2 V RMS until the end of the activation TTL pulse. This mode of operation is particularly suitable to drive solenoids, because it requires a higher voltage to start and a lower maintenance voltage. By using this circuit, power consumption and heating are reduced and the solenoid lifetime is enhanced. Moreover, this circuit is specially appropriated to build computercontrolled solenoid valves systems.