Characterization of oil complex hydrocarbon mixtures by HSQC‐NMR spectroscopy and PCA

Abstract

The degree of changes in complex mixtures from crude oil (CO) and from oil residues in soils was determined by using heteronuclear single quantum coherence–nuclear magnetic resonance (HSQC‐NMR) spectroscopy. The HSQC‐NMR spectra of crude oil samples and two oil residues with natural attenuation (E1 and E2), and two biopiles (B1 and B2) were recorded using a 500‐MHz spectrometer. The spectra could be divided into major regions according to the different types of protons and carbons. Twenty‐three regions (A1–A5, B1–B11, C1–C3, D1–D3, and E) were defined on the basis of signal assignments. A multivariate method, the principal component analysis (PCA), was used to search the change in the structural parameters during the environmental exposure time. The first two principal components (PCs) accounted for the 83.3% of the total variance (51.8% and 31.5% for PC1 and PC2, respectively). The euclidean distances (3D) between the samples are 2.80 (CO–E2), 2.37 (CO–E1), 1.62 (CO–BP1), and 1.72 (CO–BP2). This suggests that the environmental transformation during exposure time follows the order E2 > E1 > BP2 > BP1 > CO. The disappearance of the signals (−CH, −CH2, and −CH3) in the HSCQ‐NMR spectra compared with the crude oil spectrum was conveniently quantified by PCA, and it helps in the characterization of the fate of the oil spills. Copyright © 2013 John Wiley & Sons, Ltd.