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

A micro-total analytical system (μTAS) 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 μm wide and 115 μm deep in which electro-osmotic flow 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 μM with a correlation coefficient of 0.999. The RSD at 50 μM NO−2 was 2.6% (n=6) and the limit of detection obtained (3σ) was 0.20 μM NO−2.