Automated Droplet-Based Microfluidic Analyzer for Monitoring of Ammonium Ions in River Water.

Accurate monitoring of ammonium ion (NH ) levels in water bodies is fundamental for assessing water quality and potential contamination. Here, we present a novel automated droplet-based microfluidic analyzer for monitoring of NH concentrations in river water. The developed analyzer miniaturizes the modified Berthelot colorimetric method into submicroliter droplets contained within oil flow. The use of droplets enables measurements at high frequency (10 s per measurement) with low reagent consumption (0.3 μL per measurement). NH measurements showed linear responses up to 2 mg L, and a limit of detection (LOD) of 0.11 mg L. The system was tested with river water samples collected from the River Itchen (Southampton, UK), with excellent agreement ( < 0.05) between the droplet microfluidic analyzer and standard benchtop analysis. The analytical performance of this microfluidic analyzer showed that it could be applicable to sustainable monitoring of NH levels in a wide range of water bodies and scenarios, including rivers, lakes, aquaculture, and/or industrial effluents.