Screening analysis to detect adulteration in diesel/biodiesel blends using near infrared spectrometry and multivariate classification.

This paper proposes an analytical method to detect adulteration of diesel/biodiesel blends based on near infrared (NIR) spectrometry and supervised pattern recognition methods. For this purpose, partial least squares discriminant analysis (PLS-DA) and linear discriminant analysis (LDA) coupled with the successive projections algorithm (SPA) have been employed to build screening models using three different optical paths and the following spectra ranges: 1.0mm (8814-3799 cm(-1)), 10mm (11,329-5944 cm(-1) and 5531-4490 cm(-1)) and 20mm (11,688-5952 cm(-1) and 5381-4679 cm(-1)). The method is validated in a case study involving the classification of 140 diesel/biodiesel blend samples, which were divided into four different classes, namely: diesel free of biodiesel and raw vegetal oil (D), blends containing diesel, biodiesel and raw oils (OBD), blends of diesel and raw oils (OD), and blends containing a fraction of 5% (v/v) of biodiesel in diesel (B5). LDA-SPA models were found to be the best method to classify the spectral data obtained with optical paths of 1.0 and 20mm. Otherwise, PLS-DA shows the best results for classification of 10mm cell data, which achieved a correct prediction rate of 100% in the test set.