Uranine as a Tracer for Rapid Detection of Spray Deposition

Abstract

While being virtually mandatory to any sustainable agricultural activity, plant protection products pose sensible risks due to the side effects of improper application techniques.

Monitoring of the application parameters is therefore of paramount importance. In particular, one of the most interesting parameter to monitor is the deposition pattern, whose sampling is reportedly time-consuming and unreliable due to uncontrollable test conditions [9]. In this paper, we investigated a simplified deposition assessment strategy involving uranine, a non-toxic and low cost fluorescent tracer widely used in other fields [7], to minimize the measurement uncertainties exploiting the well known phenomenon of optical absorbance, thanks to the identification of a linear proportionality regime between concentration and absorption peak with coefficient of determination R² = 99%. A nozzle evaluation bench has been set up to deposit the fluorescent solution on a matrix of Petri dishes, which were then oven-dried to redissolve the residuals in a fixed amount of water. Spectrophotometry was used to retrieve the mass of deposited solution. After careful calibration against known uranine concentrations, the method yielded results very well correlated to the weight measurements performed prior to drying and allowed to trace back an approximate deposition curve. The complete evaporation of the deposited solvent allows to get rid of the unpredictable atmospheric conditions during the test, while the flexibility of the solution enables an easy tailoring of the technique to different application volumes, deposition rates or collector configurations without losing accuracy.