Characterisation of a micro-total analytical system for the determination of nitrite with spectrophotometric detection

A micro-total analytical system (mu TAS) is described for the determination of nitrite based on its reaction with sulphanilamide to form the diazonium salt which when coupled with N-(1-naphthyl) ethylene diamine yields an azo dye whose absorbance was measured at 526 nm. The reaction took place in an etched glass manifold containing channels 302 mu m wide and 115 mu m deep in which electro-osmotic how was used to move the reagents. The absorbance of the product was measured in situ using a micro-spectrophotometric-fibre optic detection system. The electro-osmotic flow mixing characteristics of the reagents together with the production of the colorimetric complex have been investigated. in addition methods for obtaining sensitive detection in the micro-reactor are reported. Using the conditions established a linear calibration was obtained between 0 and 100 mu M with a correlation coefficient of 0.999. The RSD at 50 mu M NO2- was 2.6% (n=6) and the limit of detection obtained (3 sigma) was 0.20 mu M NO2-. (C) 1999 Elsevier Science B.V. All rights reserved.