Convenient environmentally friendly on-site quantitative analysis of nitrite and nitrate in seawater based on...

Nowadays, nitrate (NO₃^-) and nitrite (NO₂^-) 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 (R² > 0.99) ranges of 0.05 to 5 mg L^-1 for nitrite and 1 to 50 mg L^-1 for nitrate were obtained and detection limits of 50 μg L^-1 for nitrite and 0.32 mg L^-1 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.