Smartphone-based detection of nitrate in seawater samples with the resorcinol method: Comparison with the vanadium reduction method.

The presence of nitrate (NO) in the aquatic environment has raised a major concern for scientists and environmental managers. In this study, a smartphone-based resorcinol method was developed for the determination of NO in seawater. Simple custom-made devices were used in the method, and the reaction temperature, reaction time, and smartphone camera settings were optimized. Salinity variation did not show any major impact on the determination of NO using the proposed method, and hence the incorporation of a correction factor was also not required. The detection limit for this method was observed to be 1.3 µM, and the working range was observed to be 5-60 µM, with a relative standard deviation of 0.7% (5 µM, n = 7), which was adequate for the determination of NO in most estuarine and coastal seawater samples. The proposed method was compared with the frequently used vanadium chloride (VCl) reduction method under the same experimental conditions, and both methods were found to be beneficial. The proposed method procedure was simple and easy to use. It was successfully applied for the determination of NO in seawater samples, and the results showed that it was practical and can be used potentially for on-site analysis.