Abstract
Accurate in situ monitoring of ammonium ion (NH(4) (+)) levels in water bodies is fundamental for assessing water quality and potential contamination. Here, we present a novel automated droplet-based microfluidic analyzer for in situ monitoring of NH(4) (+) 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(4) (+) measurements showed linear responses up to 2 mg L(-1), and a limit of detection (LOD) of 0.11 mg L(-1). The system was tested with river water samples collected from the River Itchen (Southampton, UK), with excellent agreement (p < 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 in situ monitoring of NH(4) (+) levels in a wide range of water bodies and scenarios, including rivers, lakes, aquaculture, and/or industrial effluents.