Partner und Internationale Organisationen
(Englisch)
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Danfoss A/S (Nordborg, DK); GeSiM (Dresden, D); Microelectronics Center, Danish Technical University Copenhagen (DK); Biomedical & Environmental Sensor Technology Center, Dublin City University (IRL); Suez Lyonnaise Eaux (F)
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Abstract
(Englisch)
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The core strategic goal of the MicroChem project is to demonstrate a new microfluidic sensing system, based on Micro System Technology, for applications at remote sites and in harsh environments. The basic requirements for the new sensor system are: (1) Measurements of small ion concentrations relevant for water quality, primarily nitrate, orthophosphate, and ammonia, but potentially also other pollutants like metal ions. (2) In situ measurements in waste water treatment plants, in the sewage system, and factory outlets. (3) Measurements on drinking water in lakes and other recipients, in pumping wells, and in drinking water facilities. At IMT, research efforts focused on the realization of two different microfluidic strategies for analysis of small inorganic ions in water, both of which involve manipulation of nL to mL quantities of solution in etched microchannel networks on chips.
In the first case, the Berthelot reaction was used to form an indophenol derivative of ammonia. Sample was introduced to the chip, and 3 reagents were added sequentially from side channels to form the blue-coloured compound. Absorbance measurements for the complex formed on-chip compared very well to those obtained in a spectrophotometric system. However, while this reaction is robust, the kinetics are quite slow, which can lead to lack of sensitivity (low conversion of analyte) in a monitoring situation. To optimize the reaction, alternative reagents and conditions were tested. Maximum conversion at 25°C was achieved in < 6 min, and salicylate was found to be a viable replacement for the toxic phenol reagent. The very high reproducibility and efficiency of mixing by diffusion in the microfluidic chip make it a useful tool for future studies of other chemical methods where kinetics are a limiting factor for the response time. A new, all-glass, multilayer chip technology was also developed in conjunction with this project.
The second strategy for ion analysis adopted in this project considered the integration of a fast separation technique, capillary electrophoresis, onto a chip. Species are separated in applied electric fields based on their different charge-to-mass ratios, and liquids are pumped using electro-osmotic flow. Several sample preconcentration techniques have been shown to improve limits of detection in microchip-based analysis systems. Field amplification sample stacking in a low-conductivity sample matrix was easily implemented on-chip in this project, and signal gains of almost 100-fold could be obtained. Contactless conductivity detection could also be integrated into glass devices. Limits of detection for K+ using this were improved by use of sample stacking to 10 mM. Analysis times well under 1 minute could be obtained, making this an interesting alternative for real-time, multi-ion analysis in water.
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