Next generation autonomous chemical sensors for environmental monitoring
Cogan , Deirdre and Cleary, John and Phelan, Thomas and Diamond, Dermot (2013) Next generation autonomous chemical sensors for environmental monitoring. In: CEST2013 The 13th International Conference on Environmental Science and Technology, 5-7 Sept 2013, Athens, Greece.
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Microfluidic technology has great potential as a solution to the increasing demand for environmental monitoring, by producing autonomous chemical sensing platforms at a price level that creates a significant impact on the existing market. The development of sensing platforms for ammonium, nitrate and nitrite in water and wastewater using colorimetric techniques are being investigated. Our approach is to combine microfluidic technology with colorimetric chemical assays; low cost LED/photodiode-based optical detection systems; and wireless communications, developing low cost systems which can be deployed for extended periods.
The objectives of this project are:
(i) to develop and optimise colorimetric detection methods for nitrate, nitrite and ammonia, and (ii) to integrate polymeric actuator valves into the microfluidic chip, significantly driving down the overall cost of the platform for a fully integrated, multi-target ‘matchbox’ analyser ready for field deployment.
The colorimetric study of nitrite was performed using the Griess test, and an autonomous nitrite analyser has also been developed. The work described in this paper shows that this forms the basis of a highly sensitive, low cost, simple colorimetric technique that can be integrated into a field deployable platform.
A simplified colorimetric technique for nitrate has also been established and optimised using chromotropic acid in the presence of concentrated sulphuric acid. The method shows great relevance as a linear range was achieved from 0-80mg/L NO3-. The kinetics, reproducibility, limit of detection and reagent stability was investigated. A blind test using real samples was performed and results showed excellent agreement to ion chromatography. The chromotropic method for nitrate determination has been demonstrated to be a direct, simple technique. It was also shown that it is possible to reduce the concentration of the sulphuric acid used in the assay, reducing risk factors and component cost while maximising the lifetime of the system.
A colorimetric method for the determination of ammonium was also investigated. The reagent cocktail includes a variation on the Berthelot method which employs salicylic acid instead of phenol, thereby eliminating a toxic and unstable reagent component. The intense colour generated is detected at a wavelength of 630nm.
Results for the direct determination of nitrite and ammonia achieved also suggest that these may be suitable for integration into a similar field deployable platform to that of a phosphate monitoring platform which was previously developed1. Results from recent deployments of the phosphate platform in situ at Broadmeadow Water Estuary, Co. Dublin, Ireland, and at a constructed wetlands wastewater treatment system at Glaslough, Co. Monaghan, Ireland from May to June 2012 are also presented.
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