Simultaneous determination of sulfur, nitrogen and ash for vegetable tannins using ATR-FTIR spectroscopy and multivariate regression

The quantification of sulfur, nitrogen and ash content in tannins of mimosa (Acacia mearnsii) and quebracho (Schinopsis sp.) is of fundamental importance for its industrial use. Thus, an analytical method capable of identifying these properties by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was developed using multivariate regression methods. Partial least squares regression (PLS) method was used as well as the interval partial least squares (iPLS) and the synergy interval partial least squares (siPLS). The developed models were compared based on the root of the mean square errors (RMSE) and determination coefficients (R2). The results showed that both the iPLS and the siPLS, using the infrared data, obtained satisfactory results, but having a small improvement with the use of the siPLS. In general, the proposed method does not require reagent consumption, being much faster than traditional techniques, allowing potential applications for simultaneous determination of sulfur, nitrogen and ash contents for routine analysis of plant tannins by FTIR data.