A new approach to construct diffusion/permeation cell for use in flow systems: application in the spectrophotometric determination of bicarbonate ions

Abstract

Este artigo descreve uma nova abordagem para construção de módulos de difusão/permeação de gás, baseado no perfeito encaixe entre dois blocos de acrílico. A cela foi empregada para determinação de íons bicarbonato, explorando a descoloração de uma solução 0,01% (m/v) de fenolftaleína em meio alcalino (pH 9,0). A variação da coloração do indicador foi monitorada em 552 nm. A curva analítica exibiu faixa linear entre 25,0 e 150,0 mg L -1 em NaHCO 3 . Os sinais obtidos a partir de injeções consecutivas (n=10) de uma solução padrão 5,0 mg L -1 resultaram em desvio padrão relativo menor que 1,0%. O coeficiente de correlação da curva analítica foi 0,9996 e o limite de detecção (3 x ruído/coeficiente angular) 4,41 mg L -1 de NaHCO 3 . O método proposto é rápido (até 50 amostras/hora) e os resultados estão em boa concordância com os obtidos por titulação clássica.This work describes a new approach for construction of gaseous diffusion/permeation module in a configuration based on the perfect fitting between two plaques of acrylic. It was employed to determine bicarbonate ions exploiting the discoloration of a 0.01% (m/v) phenolphthalein solution in medium of 1.0 x 10 -5 mol L -1 NaOH (pH 9.0). The variation in the indicator color was monitored at 552 nm. The analytical curve showed a working range between 25.0 and 150.0 mg L -1 in NaHCO 3 . Consecutive injections (n=10) of a standard 5.0 mg L -1 NaHCO 3 solutions exhibited less than 1.0% of relative standard deviation. The correlation coefficient of analytical curve was 0.9996 and the limit of detection (3 x noise/slope) is 4.41 mg L -1 in NaHCO 3 . The proposed method is rapid (50 sample/hour) and results were in good agreement with the ones obtained by classical titrimetry. Keywords: gas-diffusion device, flow injection analysis, bicarbonate ions IntroductionPhase separations associated to flow injection systems are strategies quite used to improve the selectivity of analytical methods, as well as to perform pre-concentration of chemical species.1-4 Phase separations involving liquid/ liquid, 5-7 gas/solid and gas/liquid extractions 8,9 are applied in many cases to eliminate chemical interferences and matrix effects. The applications of these approaches in flow injection systems reduce the time of analysis considerably, making possible the direct analysis of complex samples, and saving sample and reagents. 10,11 The uses of gaseous diffusion module for the analytical control of chemical species contained in many commercial products are of great interest. Among that species are sulfite, [12][13][14] and others. These substances can occur either naturally, as in the case of the presence of bicarbonate in mineral waters, or they can be intentionally added to confer especial properties to the product, increasing the 977 A New Approach to Construct Diffusion/Permeation Cell Vol. 17, No. 5, 2006 biochemical stability and chemical resistance to oxidation. The analytical control of those species by flow injection analysis is commonly made with the employment of gas/liquid...

Membrane-based Separation in Flow Analysis for Environmental and Food Applications

“…Successful applications of this hyphenation can be observed in: the determination of bromide and sulfide in tap and wastewater by spectrophotometry (50,55); chlorine dioxide in water by fluorescence (47); and ammonia and inorganic carbon in water with an acidbased indicator by spectrophotometry (42,44), conductimetry (36,38,56,58) and fluorescence (41,49). Due to the high selectivity of GD membranes, most of the methods combine membrane-based separations with non-selective detectors such as spectrophotometric and conductimetric detection where the color change of acid-base indicators or conductivity changes are measured (36,38,40,42,44,48,50,(54)(55)(56)58,59). Fluorescence and chemiluminescence detectors are usually chosen when lower detection limits are intended as these are sensitive techniques (37,39,41,43,47,49).…”