Estimating of Brazilian charcoal properties using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometry coupled with multivariate analysis
Charcoal; Volatile Matter Content; ATR/FTIR spectroscopy; PLS; Variable Selection; Significance testing.
The aim of the present work was to estimate fixed-carbon, volatile matter content and ash in Brazilian commercial charcoal by using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) together with multivariate calibration methods. Several multivariate calibration techniques, including partial least squares (PLS), interval partial least squares (iPLS), genetic algorithm (GA), were compared and validated by establishing significance testing (t-test and Shapiro-Wilk test). Charcoal samples (n = 72) were divided into calibration (n = 52) and validation sets (n = 20) by applying the classic Kennard-Stone (KS) selection algorithm to the ATR-FTIR spectra. For fixed-carbon content, the result obtained using PLS-GA for the root mean square error of cross validation (RMSECV) and prediction (RMSEP) were 3.77% and 4.29%, respectively. For volatile matter, RMSECV and RMSEP of 4.36% and 4.65% was achieved by PLS model using seven latent variables (LV). Finally, for ash, RMSECV and RMSEP of 0.58% and 0.38% was achieved by PLS model using eight latente variables (LV). A t-test and Quantile-quantile (Q–Q) plot were performed to compare the results of the models with each other and with a reference method. These results suggest that ATR–FTIR spectroscopy and multivariate calibration can be effectively used to determine fixed-carbon, volatile matter content and ash content in Brazilian charcoal.