Development of a methodology for phosphorus determination in soils, water, and biofertilizer using digital image analysis - DIA

Abstract

A new methodology based on Digital Image Analysis (DIA) was developed to determine the phosphorus content in different matrices of soil, aqueous standards, and biofertilizers. P was extracted by the Mehlich-1 method (0.05 mol L−1 HCl + 0.0125 mol L−1 H2SO4), with modifications, where the concentrations of complexing agent ammonium molybdate (AMC), bismuth subcarbonate (SBC) and ascorbic acid mass (AAM) were studied for the formation of the blue phosphomolybdic complex. A 23 factorial design and Dohelert matrix were applied for the study, in addition to the optimization of the variables. A light box was developed to optimize the conditions for obtaining images through smartphones, such as exposure to artificial and natural light and the resolution of smartphone cameras. Images were processed using ImageJ and Chemostat to obtain RGB values. Responses were expressed in terms of the logarithmic function of the ratio between the blank signal and the measured signal Log (R0/R), which showed the best sensitivity with good linear correlation (R2 = 0.9795). The methodology was successfully applied to soil, aqueous standards, and biofertilizer samples. The results did not differ statistically from the values found in the application of the conventional spectrophotometric methodology for α = 0.05. The limits of detection and quantification found in the DIA were, respectively, 1.60 and 2.30 mg dm−3. Addition and recovery tests on aqueous standards, resulted in recoveries between 94 and 102%. The developed methodology is suitable for the determination of P in different matrices such as soil, aqueous standards, and biofertilizers using smartphones.