Rapid assessment of fertilizers manufacturing methods by means of a novel waveguide vector spectrometer
Purpose: The present study aims to test the suitability of a waveguide spectrometer, as a rapid and cheap tool to discriminate different fertilizers according to two different manufacturing methods, such as granulation and blending. Methods: The tested instrument is a waveguide vector spectrometer, patented in 2016, that operates in the range 1.6-2.7 GHz, giving both spectral phase and gain measurements. Granulated and blended fertilizers were dehydrated and pulverized, to avoid possible interferences related to the water content and geometry of the sample. The spectral data were analyzed by multivariate statistical analysis (Principal Component Analysis, PCA and Partial Least Squares-Discriminant Analysis, PLS-DA) in order to obtain a discrimination tool considering the whole hidden spectral information. Results: Principal Component 1 (95% of the explained variance) and Principal Component 2 (4% of the explained variance) shown to explain most part of the spectral variability. A tendency to group samples according to the different production methods can be appreciated even if the discrimination is influenced by the different chemical composition of fertilizers. However, PLS-DA models correctly classified 100% of the samples both by granulated and blended classes using spectra obtained by waveguide spectroscopy. Conclusions: Although preliminary, the tests carried out on a small number of samples show how the technique coupled with PLS-DA models could be able to discriminate the analyzed fertilizers by means of their spectral signature and according to the manufacturing method if the chemical composition is kept constant. Further tests are necessary to validate the model, also considering the possibility of grouping fertilizers for similar composition.
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