Visible LED-Based Instrumentation for Photometric Determination of Electroosmotic Flow in Microchannels

An instrumental setup for electroosmotic flow (EOF) determination in microfluidic devices is described. The system is based on a trinocular microscope and an integrated photodiode OPT101. The radiation was provided by a high-intensity white LED. For the determinations, patent blue V and methylene blue aqueous solutions were used. The setup was applied for EOF monitoring in hybrid toner/glass and PDMS microchips. For the toner/glass device, the EOF mobility was determined to be (5.75 ± 0.01) 10-4 cm² V-1 s-1 at pH 7.0. For PDMS devices the measured EOF mobility was (3.2 ± 0.1) 10-4 cm² V-1 s-1. Reproducible measurements were obtained in all experiments, which produced results with small errors. The proposed method was compared to the conventional current monitoring method

Visible LED-Based Instrumentation for Photometric Determination of Electroosmotic Flow in Microchannels

An instrumental setup for electroosmotic flow (EOF) determination in microfluidic devices is described. The system is based on a trinocular microscope and an integrated photodiode OPT101. The radiation was provided by a high-intensity white LED. For the determinations, patent blue V and methylene blue aqueous solutions were used. The setup was applied for EOF monitoring in hybrid toner/glass and PDMS microchips. For the toner/glass device, the EOF mobility was determined to be (5.75 ± 0.01) 10-4 cm² V-1 s-1 at pH 7.0. For PDMS devices the measured EOF mobility was (3.2 ± 0.1) 10-4 cm² V-1 s-1. Reproducible measurements were obtained in all experiments, which produced results with small errors. The proposed method was compared to the conventional current monitoring method.A instrumentação para a determinação fotométrica do fluxo eletrosmótico (EOF) em dispositivos microfluídicos é descrita neste trabalho. A instrumentação é baseada em componentes acessíveis e consiste em um microscópio trinocular e no fotodiodo integrado OPT101. Um diodo emissor de luz (LED) de alta intensidade foi utilizado como fonte de radiação. Para as determinações foram utilizadas soluções aquosas dos corantes azul patente V e azul de metileno. O sistema foi utilizado no monitoramento do EOF em microdispositivos de poli(dimetilsiloxano) (PDMS) e híbridos de toner/vidro. As mobilidades do EOF determinadas em pH 7,0 foram (5,75 ± 0,01)10-4 cm² V-1 s-1 e (3,2 ± 0,1)10-4 cm² V-1 s-1 para os dispositivos de toner/vidro e PDMS, respectivamente. Medidas reprodutíveis foram obtidas em todos os experimentos, levando a uma alta precisão na determinação. O método proposto foi comparado com o método tradicional de determinação do EOF que envolve a medida da corrente nos microcanais.736740Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

A Rapid and Simple Method for Determination of 5-Hydroxytryptophan in Dietary Supplements by Capillary Electrophoresis

A rapid and simple capillary electrophoresis (CE) method was developed to determine 5-hydroxytryptophan (5-HTP) in samples of commercial dietary supplements. The optimized background electrolyte (BGE) was composed by 20 mmol L-1 sodium phosphate (pH 10) and 0.2 mmol L-1 cetyltrimethylammonium bromide (CTAB) for electroosmotic flow inversion. The limits of detection (LOD) and quantification (LOQ) for 5-HTP were 3.1 and 10.1 µmol L-1, respectively. The analytical curve demonstrated linearity over a concentration range of 0-500 µmol L-1 with a correlation coefficient (R²) of 0.9995. The intraday instrumental precision (repeatability) as relative standard deviation (RSD) in terms of peak area and migration time of the 5-HTP were 2.2 and 1.9% (n = 8), respectively. The CE method was applied to the analysis of four different samples of commercial dietary supplements and the RSD (n = 3) for the determinations ranged from 2 to 3%. The accuracy of the method was evaluated comparing the measured 5-HTP concentrations to those obtained by a high performance liquid chromatography (HPLC) method. The relative error ranged from 0 to 5.9% (n = 3) and no significant differences between the concentrations were observed at a confidence level of 95%

Desenvolvimento de um detector piezelétrico para cromatógrafo a gás interfaceado a microcomputador

A piezoelectric detector based on a commercial quartz crystal of 3.57MHz is shown. A PTFE cell attached to the GC-column outlet holds the polymer-coated crystal, whose terminals were removed. Two TTL oscillators (reference and sensor) are used and the beating of their frequencies is monitored through a home-made counter card inserted in a microcomputer. The original thermal conductivity detector was also interfaced, but through a 12-bit analog-to-digital converter. In spite of the well-known fact that QCM has low sensitivity at high temperatures, results show significant peak deformation for low temperatures. In addition, the phenomenon is also dependent on the chemical composition of the absorbent film besides instantaneous partial pressure and chemical composition of the analyte

Improving the sensitivity of electrode-separated piezoelectric quartz crystal sensor for copper(II) ions by immobilization of the N-2-aminoethyl-3-aminopropylsilane group

An electrode-separated piezoelectric quartz crystal sensor with a chemically modified surface was proposed. The modification was carried out by a silanization procedure with N-2-aminoethyl-3-aminopropyltrimethoxysilane, yielding the immobilised N-2-aminoethyl-3-aminopropylsilane group over the surface of a 3.5 MHz piezoelectric quartz crystal. A flow cell was manufactured with poly(methyl methacrylate) and brass, instead of noble metals, for the electrodes. In this cell, the solution touches only one side of the crystal and the related electrode is coated with a polyester film, which prevents corrosion and does not disturb the oscillation process. This innovation reduces the cost of the cell and renders an electronics non DCcoupled to the solution. The modified crystal proved to be more sensitive to copper(II) ions than magnesium(II), nickel(II), zinc(II), and cobalt(II). For 100muL sample injections, the limit of detection for copper(II) was 6 mumol L-1, which is an impressive result when compared with that for an unmodified crystal

Improving the sensitivity of electrode-separated piezoelectric quartz crystal sensor for copper(II) ions by immobilization of the N-2-aminoethyl-3-aminopropylsilane group

An electrode-separated piezoelectric quartz crystal sensor with a chemically modified surface was proposed. The modification was carried out by a silanization procedure with N-2-aminoethyl-3-aminopropyltrimethoxysilane, yielding the immobilised N-2-aminoethyl-3-aminopropylsilane group over the surface of a 3.5 MHz piezoelectric quartz crystal. A flow cell was manufactured with poly(methyl methacrylate) and brass, instead of noble metals, for the electrodes. In this cell, the solution touches only one side of the crystal and the related electrode is coated with a polyester film, which prevents corrosion and does not disturb the oscillation process. This innovation reduces the cost of the cell and renders an electronics non DCcoupled to the solution. The modified crystal proved to be more sensitive to copper(II) ions than magnesium(II), nickel(II), zinc(II), and cobalt(II). For 100muL sample injections, the limit of detection for copper(II) was 6 mumol L-1, which is an impressive result when compared with that for an unmodified crystal