On-site detection of nitrate plus nitrite in natural water samples using smartphone-based detection

Abstract

Nitrate plays an important role in the nitrogen cycle and is also a known pollutant of the aquatic ecosystem. Rapid, sensitive, and on-site analysis of nitrate is helpful for biogeochemical study of nitrogen and evaluation of water quality. In this study, a simple green manual method based on the VCl3 reduction-Griess reaction was established for nitrate analysis. The effects of reaction parameters including temperature, reagent concentration, salinity, and nitrite content on nitrate determination were comprehensively evaluated and optimized using a standard laboratory spectrophotometer. This method exhibited a detection limit of 0.15 μmol L−1, relative standard deviations of less than 1%, and an analytical range as high as 60 μmol L−1 before dilution. As many as 20 samples were measured within 1 h. Different natural water samples (n = 60) with various salinities were measured with excellent accuracy (<3% error) and high recovery (94–105%). Real on-site detection was achieved using smartphone-based detector. There was a good linear relationship between the intensity of green channel and the concentration of nitrate up to 20 μmol L−1 (R2 = 0.9988). There is no significant difference of detection results between spectrophotometer and smartphone in practical application (t-test, p = 0.97 > 0.05). The proposed method is salinity-interference-free, robust, and easy-to-operate, which make it suitable for both laboratory routine and on-site analysis.