Rapid determination of nitrate in drinking water based on image processing techniques using a smartphone platform

This study presents a portable and low-cost smartphone-based kit for fast nitrate-level-detection in drinking water using a commercially available nitrate indicator and image processing techniques. The colour intensity in photos taken from indicator-added water samples was correlated to the concentration of nitrate ions. Converting Matlab codes to Android platform allowed us to determine the nitrate concentration in water samples using a smartphone. The newly designed technique provided agreeable LOD and LOQ values (respectively 1.50 and 5.0 µg mL–1), and favourable R2 (0.995) for matrix-matched calibration in close accordance with UV-visible spectroscopy. The obtained LOQ is well below the maximum residual level for nitrate in drinking water (50 µg mL–1, set by WHO). Field applicability of the smartphone-based technique was investigated by measuring the nitrate level in drinking water samples, collected from forty-two different zones in Tehran and Alborz (central Iran provinces). The results were in close accordance with those achieved from UV-visible spectrometry. Thus, the proposed method, as an alternative technique to expensive and intricate conventional techniques, could be used for rapid determination of the nitrate in drinking water samples.