Colorimetric analyzer based on mobile phone camera for determination of available phosphorus in soil

• Smart phone was used for colorimetric determination of phosphorus in soil.
• The software on Android OS was developed for photo capture and analysis of RGB color.
• Controlled illumination during photo taking is necessary for high precision and accuracy.
• Results obtained were correlated well with spectrophotometry.
• The developed analyzer is simple, portable, and provides fast, convenient, on-site analysis.

A field deployable colorimetric analyzer based on an “Android mobile phone” was developed for the determination of available phosphorus content in soil. An inexpensive mobile phone embedded with digital camera was used for taking photograph of the chemical solution under test. The method involved a reaction of the phosphorus (orthophosphate form), ammonium molybdate and potassium antimonyl tartrate to form phosphomolybdic acid which was reduced by ascorbic acid to produce the intense colored molybdenum blue. The software program was developed to use with the phone for recording and analyzing RGB color of the picture. A light tight box with LED light to control illumination was fabricated to improve precision and accuracy of the measurement. Under the optimum conditions, the calibration graph was created by measuring blue color intensity of a series of standard phosphorus solution (0.0–1.0 mg P L−1), then, the calibration equation obtained was retained by the program for the analysis of sample solution. The results obtained from the proposed method agreed well with the spectrophotometric method, with a detection limit of 0.01 mg P L−1 and a sample throughput about 40 h−1 was achieved. The developed system provided good accuracy (RE<5%) and precision (RSD<2%, intra- and inter-day), fast and cheap analysis, and especially convenient to use in crop field for soil analysis of phosphorus nutrient.

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