Real-time smartphone-based multi-parameter detection of nitrite, ammonia nitrogen, and total phosphorus in water

Elevated levels of ammonia nitrogen and phosphorus trigger eutrophication, spurring algal blooms, depleting oxygen, and thereby degrading water quality and killing fish. Nitrites, toxic to humans and animals, contaminate water sources when present in excess, making the water unfit for drinking and making their removal <i>via</i> standard treatments challenging. Together, these factors severely endanger aquatic life, human health, and water safety. Thus, developing on-site quantitative methods for the determination of nitrite, ammonia nitrogen, and total phosphorus in environmental waters is of great significance for environmental monitoring agencies. This study introduces a fast, cost-effective, and flexible on-site testing method that leverages a smartphone and a self-designed 3D-printed portable device to detect nitrite, ammonia nitrogen, and total phosphorus in environmental water. This constitutes an on-site analysis approach as it involves portable equipment deployed at the field location, rather than <i>in situ</i> sensing that directly probes samples within their native environment without collection. The method utilizes the smartphone's color recognition feature and an adaptive deconvolution algorithm that allows for the simultaneous detection of these pollutants using a six-channel device under optimal conditions. The detection limits for nitrite, ammonia nitrogen and total phosphorus were 0.013, 0.14 and 0.034 mg L^-1, respectively. Furthermore, the linear ranges for nitrite, ammonia nitrogen and total phosphorus were 0.02-0.86, 0.18-2.25 and 0.04-1.65 mg L^-1, respectively, and their recoveries were in ranges of 90.2 ± 1.8-108.4 ± 6.8%, 84.0 ± 7.4-107.3 ± 5.5%, and 93.8 ± 7.5-107.6 ± 2.7%, respectively. This method offers a quick, precise, and sensitive alternative to traditional analysis, reducing analysis time, minimizing sample contamination and errors, and thus providing a convenient and efficient solution for the on-site environmental monitoring of ammonia nitrogen, nitrite, and total phosphorus, suitable for rapid water quality detection.