Fig. 1. Mean mass spectra of the three crude oils studied: (a) Brass River Light crude oil; (b) Olmeca crude oil; (c) Tintal crude oil.

Fig. 2. Contour surfaces with time and mass/charge ratio axes corresponding to a sample of Olmeca crude oil.

Fig. 3. Contour surfaces for the mass/charge ratio range between 50 and 89: (a) Brass River Light crude oil; (b) Olmeca crude oil; (c) Tintal crude oil.

Fig. 4. Contour surfaces for the mass/charge ratio range between 90 and 120: (a) Brass River Light crude oil; (b) Olmeca crude oil; (c) Tintal crude oil.

Fig. 5. Contour surfaces for the mass/charge ratio range between 121 and150: (a) Brass River Light crude oil; (b) Olmeca crude oil; (c) Tintal crude oil.

Fig. 6. Single linkage dendrogram obtained with hierarchical cluster analysis for samples spiked with Brass River Light, Olmeca, and Tintal crude oils.

Fig. 7. Scores on the two principal components obtained for samples spiked with Brass River Light (□), Olmeca (○), and Tintal () crude oils.

Fig. 8. Coomans plots for the classification model constructed for commercial clean sand (left part) and Vertisol (right part) with the training set of samples. Samples of class 1 are polluted with Brass River Light (□) crude oil; samples of class 2 are polluted with Olmeca (○) crude oil; and samples of class 3 are polluted with Tintal () crude oil.

Fig. 9. Coomans plots for the prediction (using the SIMCA model in Fig. 8) of an external validation set for commercial clean sand (left part) and Vertisol (right part). Symbols as in Fig. 8.

Fig. 10. Coomans plots for the classification (left part) and for the prediction (right part) constructed jointly with commercial clean sand and Vertisol. Classes and symbols are the same as in Fig. 8.