Convenient environmentally friendly on-site quantitative analysis of nitrite and nitrate in seawater based on polymeric test kits and smartphone application.

Nowadays, nitrate (NO) and nitrite (NO) in aquatic ecosystems have increased due to various anthropogenic activities leading to deterioration of the ecosystem and can accelerate eutrophication. A Griess reagent-doped hydrogel test kit and a zinc powder-doped starch film were thus developed for on-site quantitative analysis of nitrate and nitrite. A clear colorless hydrogel tablet (diameter 1.5 cm 2 mm thickness) turned pink-violet after reacting with a standard solution of nitrite while the gray zinc-doped starch film (8.36 μm thickness) fabricated on the inner lid of small plastic tube was used for the in-tube reduction of nitrate to be nitrite. The use of this film followed by nitrite testing using the hydrogel tablet was used as a nitrate test. Both the materials developed were used in conjunction with digital image colorimetry (DIC) using smartphone application for on-site quantitative analysis of nitrite and nitrate. Good linearity (R > 0.99) ranges of 0.05 to 5 mg L for nitrite and 1 to 50 mg L for nitrate were obtained and detection limits of 50 μg L for nitrite and 0.32 mg L for nitrate were achieved. Good accuracy was obtained in terms of a relative error in a range of 0.75 to 2.68% with inter-day precision in a range of 0.20 to 0.50%RSD (n = 3). Quantitative analysis of nitrate and nitrite in 10 seawater samples taken in Phuket was in good agreement with the standard method (95% confidence level). Since the method developed employs test kits synthesized using biodegradable polymers and DIC using a smartphone application, it will allow the rapid on-site quantitative detection of nitrate and nitrite in a more convenient and environmentally friendly system.