Characterization of naphthenic acids using mass spectroscopy and chromatographic techniques: study of technical mixtures

Abstract

By the classical definition naphthenic acids (NAs) are a complex mixture of monocarboxylic acids containing one or more alkyl-substituted alicyclic rings or only aliphatic carbon chains. Based on the great interest of the oil industry in the elucidation and characterization of naphthenic acids in petrochemical samples, and the lack of efficient methodologies for the total characterization of these compounds, the goal of this study is to compare three techniques (GC/qMS, ESI-MS/MS and GC × GC/TOF-MS) for the analysis of two technical mixtures of NAs. The results presented here demonstrate the applicability of these techniques and the main advantages of each one. GC/qMS is widely used in the naphthenic acid analysis and still presents a good performance; however the ESI-MS-MS allowed a very quick analysis that provided a general profile of each sample, very useful in preliminary classification of petrochemical mixtures, while GC × GC/TOF-MS delivered a thorough evaluation of the different components of each sample. Technical mixtures analyzed showed different profiles confirmed through the three techniques applied. The mixture SA (Sigma Aldrich) presented a predominance of aliphatic acids (Z = 0) while the mixture MN (Miracema-Nuodex) was composed mainly of naphthenic monocyclic acids.