Desenvolvimento de metodologia alternativa através da espectroscopia aliada a métodos quimiométricos na quantificação de fósforo e nitrogênio em águas superficiais para abastecimento

Abstract

An alternative methodology was developed aiming the determination of phosphorus and nitrogen in urban water supply. The objective of this study was to promote the use of the spectrophotometric technique in the region of UV-Vis (Ultraviolet and Visible), in order to decrease the use of reagents, waste production and enabling faster analysis. It was created a model by using the software Matlab and PLS method (Partial Least Squares), which performs a regression between the UV-Vis spectro of the water samples and values of phosphorus and nitrogen concentration obtained by the reference method, which in this study was the colorimetry. To obtain a robust model, some tools for identifying anomalous samples were used. The values of the Root Mean Square Error of Calibration (RMSEC) and Validation (RMSEP), and the Correlation Coefficient (R), were evaluated as indicators of accuracy of the developed models. In the model built for phosphorus determination the values RMSEC, RMSEP and R were 1.4107; 1.5850 and 0.7511, while to nitrogen the values were 0.5322; 0.6960 and 0.8017, respectively. The results were also evaluated through a confidence ellipse, where it was possible to say that there was no significant difference between both methods with 95% of confidence. The linearity of the model was evaluated by the Student residues chart, which showed a normal distribution. Through the regression coefficient in both models is possible to say that all wavelengths used were important to the performance of multivariate models. Thus, the results obtained suggest that the UV-Vis spectroscopy combined with multivariate calibration through PLS method are promising in determining phosphorus and total nitrogen in water from supply.