Direct Insertion Probe-Mass Spectrometry (DIP-MS) Maps and Multivariate Analysis in the Characterization of Crude Oils

Crude oils are complex organic mixtures, with their composition changing not only with the geographical region but also with the oil field. Chemical fingerprinting of crude oils and the knowledge of dependence of their macrophysical properties from the major chemical characteristics are fundamental to both upstream and downstream operations. Direct insertion probe-mass spectrometry (DIP-MS), on the basis of the introduction of samples without previous manipulation directly into the ionization chamber, their vaporization, and eventual ionization by electronic impact, appears as a proper tool to map crude oil characteristics. The components of the oils are separated according to their boiling points up to masses of m/z 950. A set of crude oils of different origin and bulk physical properties were characterized by DIP-MS in a fast and easy way. The data represented in contour plots, with molecular weight and volatility (i.e., vaporization temperature) on the axes, gave immediately an idea of the nature of the oil in terms of its physical properties and allowed for its fingerprinting. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied to analyze contour plots, showing similarities and differences among the crude oils, confirmed by a comparison to bulk physical properties, such as American Petroleum Institute (API) gravity and viscosity.