The total acid number (TAN) was determined in the atmospheric residue (AR) and vacuum residue (VR) of the petroleum distillation process using mid-infrared spectroscopy with attenuated total reflection in association with chemometric methods. Calibration and prediction sets consisted of 44 and 13 samples, respectively (16 AR samples and 41 VR samples). Calibration models were developed using three variableselection models: interval partial least squares (iPLS), synergy interval partial least squares (siPLS), and backward interval partial least squares (biPLS). Different treatments and preprocessing steps were also evaluated for development of the models. The treatment based on the first derivative with a SavitzkyGolay filter and the mean centered was selected for model construction. A root-mean-square error of prediction of 0.164 mg g -1 of KOH was achieved using the biPLS algorithm with spectra divided into 20 intervals and combinations of

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The amount of amoxicillin in pharmaceutical formulations was determined using spectra of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)

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An alternative method for the quantifi cation of sulphametoxazole (SMZ) and trimethoprim (TMP) using diffuse refl ectance infrared Fourier-transform spectroscopy (DRIFTS) and partial least square regression (PLS) was developed. Interval Partial Least Square (iPLS) and Synergy Partial Least Square (siPLS) were applied to select a spectral range that provided the lowest prediction error in comparison to the full-spectrum model. Fifteen commercial tablet formulations and forty-nine synthetic samples were used. The ranges of concentration considered were 400 to 900 mg g -1 SMZ and 80 to 240 mg g -1 TMP. Spectral data were recorded between 600 and 4000 cm -1 with a 4 cm -1 resolution by Diffuse Refl ectance Infrared Fourier Transform Spectroscopy (DRIFTS). The proposed procedure was compared to high performance liquid chromatography (HPLC). The results obtained from the root mean square error of prediction (RMSEP), during the validation of the models for samples of sulphamethoxazole (SMZ) and trimethoprim (TMP) using siPLS, demonstrate that this approach is a valid technique for use in quantitative analysis of pharmaceutical formulations. The selected interval algorithm allowed building regression models with minor errors when compared to the full spectrum PLS model. A RMSEP of 13.03 mg g -1 for SMZ and 4.88 mg g -1 for TMP was obtained after the selection the best spectral regions by siPLS.