HSQC-NMR spectroscopy and exploratory data analysis of crude oil residue in relation to the time of spill.

Eight oil residues extracted from crude oil spill sites have been investigated for natural attenuation using heteronuclear single quantum coherence nuclear magnetic resonance spectroscopy (2D HSQC NMR). Using the exploratory data analysis (EDA) techniques; principal component analysis (PCA) and hierarchical cluster analysis (HCA), the predictive ability of the NMR technique with respect to similarities and differences in the composition of the oil residue over time was explored. The first three PCs from PCA accounted for 87% of the total variance while three clusters each were obtained from HCA analysis based on similarity in samples and NMR areas. Both exploratory analyses revealed that the -CH/-CH types, aliphatic, and aromatic content of the oil residue are the main factors responsible for compositional differences. The Euclidean distance constructed from PCA indicated real differences between fresh crude oil, aged, and younger residue. If the exposure time of the oil spill is known, HSQC coupled with exploratory data analysis would be a useful tool in evaluating the structural and compositional transformation of oil residue in the environment. This may be useful as a guide in deciding which remediation strategy is implemented in an oil spill environment like the Niger Delta region.