Assessing Biodegradation in the Llanos Orientales Crude Oils by Electrospray Ionization Ultrahigh Resolution and Accuracy Fourier Transform Mass Spectrometry and Chemometric Analysis Boniek G. Vaz,* ,†,‡ Renzo C. Silva,* ,§ Cle ́ cio F. Klitzke, † Rosineide C. Simas, † Heliara D. Lopes Nascimento, † Rosana C. L. Pereira, †,∥ Diego F. Garcia, ⊥ Marcos N. Eberlin,* ,† and De ́ bora A. Azevedo* ,§ † Laborató rio ThoMSon de Espectrometria de Massas, Universidade Estadual de Campinas, Instituto de Química, Campinas, SP, 13083-970, Brazil ‡ Universidade Federal de Goia ́ s, Instituto de Química, Campus Samambaia, Goiâ nia, GO, 74001-970, Brazil § Universidade Federal do Rio de Janeiro, Instituto de Química, Ilha do Fundã o, Rio de Janeiro, RJ, 21949-900, Brazil ∥ Petroleo Brasileiro S/A − Petrobras, CENPES, Rio de Janeiro, RJ, 21941-901, Brazil ⊥ Instituto Colombiano del Petró leo, ICP/ECOPETROL, Bucaramanga, Colombia ABSTRACT: Focusing on the O 2 class, a set of crude oils from Llanos Orientales Basin, Colombia, were classified in terms of biodegradation levels using negative ion mode electrospray Fourier transform ion cyclotron resonance mass spectrometry (FT- ICR MS) and chemometric analysis. The O 2 class, which is mainly composed of naphthenic carboxylic acids, was monitored because these polar crude oil constituents are known to be substantially affected by microbial activity. Principal component analysis (PCA) applied on the O 2 profile was able to classify the crude oils into three groups: biodegraded, mixture, and non- biodegraded. From the relative abundances of the O 2 class, a clear trend on acid distribution could be directly correlated with biodegradation: a rising in abundance of saturated acids with low double-bond equivalent (DBE) values (despite the lowering observed for fatty acids with DBE = 1), expressed by the A/C index. The combined use of two indexes, the A/C index and a new index also based on saturated acid abundances, the SA index, is proposed as an effective strategy to monitor biodegradation. This approach showed to be particularly useful to fill blanks on discrete biodegradation classification and when samples are actually composed of a mixture of oils with contrasting biodegradation levels. Results are in good agreement with predictions based on classical hydrocarbon biomarker analysis. ■ INTRODUCTION Mass spectrometry developments have been historically linked in several occasions to the enormous analytical challenges encountered in the oil industry. 1 Major advances in petroleum analysis have also been recently made using mass spectrometry as both a separation and a characterization technique. 1 Soft ionization techniques such as electrospray ionization (ESI) 2,3 and ultrahigh resolution and ultrahigh accuracy mass analyzers, typically Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), 4,5 have been successfully used in crude oil analysis. These techniques have contributed to the challenge of petroleum analysis via Petroleomic, which aims to provide comprehensive characterization of the organic and inorganic composition of petroleum and its derivatives and products. 6−10 FT-ICR MS has been the technique of choice for direct crude oil analysis due to the colossal complexity of its chemical composition and its ultrahigh resolution and accuracy, which enables the separation by mass of thousands of components in a single mass spectrum acquisition. Although less polar or nonpolar hydrocarbons predominate in crude oils, the ESI technique has been used extensively to investigate the polar species, detected basically as protonated or deprotonated molecules, which have been shown to function as proper indicators for many oil properties such as acidity, thermal evolution, treatment resistance, and biodegradation. 11−15 Traditional geochemical evaluation of crude oils uses molecular composition of the saturated or aromatic hydro- carbon fractions and a series of biomarkers to infer about maturity, biodegradation, organic matter origin, and to perform oil−oil and oil−rock correlations. 16 The microbial crude oil alteration may however provide misleading predictions via biomarker analysis, for instance, due to modifications in molecules used for access thermal maturity. 16,17 Alternative biomarkers for biodegraded oils and new biodegradation parameters to evaluate biodegradation have therefore been proposed. 18−22 Biodegradation extent could also be inferred by quasi-stepwise scales, 16,23,24 but it is still quite difficult to achieve a global scheme because most oils are composed of a mixture of different oils or biodegraded through inconsistent patterns. 25 For the analysis of the saturated hydrocarbons in crude oil, gas chromatography (GC) coupled to mass spectrometry (MS) has been the reference technique for many years. 16,26,27 More Received: October 31, 2012 Revised: February 27, 2013 Published: March 1, 2013 Article pubs.acs.org/EF © 2013 American Chemical Society 1277 dx.doi.org/10.1021/ef301766r | Energy Fuels 2013, 27, 1277−1284