Detection and quantification of phosphate in water and soil using a smartphone

Abstract We report here a low-cost, field-deployable smartphone-based sensing system for accurate estimation of phosphorus (in phosphate form) in water and agricultural soil. The sensing principle is based on the standard ascorbic acid protocol where heteropoly acid-phosphomolybdic acid reagent changes color upon treatment with ascorbic acid, which can be detected by the designed sensing system. A 3D printed cradle housing the optical source and other optical components of the sensor is coupled to the built-in rear camera of the phone and subsequently, convert it into a compact handheld system. Two freely available android applications have been used for the detection and analysis of phosphate concentration. The HSV (Hue-Saturation-Value) color model's V-channel values of the captured images are used to correlate with the phosphate concentrations of the samples. The results obtained with the proposed sensor are found similar to laboratory-grade spectrophotometer data. The designed sensing system has an ability to measure phosphate concentration variations as low as 0.01 mg/L and 0.03 mg/L in the range 0–1 mg/L and 1–5 mg/L, respectively, with good accuracy (%bias