Profiling Free Naphthenic Acids in Produced Water Using Gas Chromatography Coupled to High Resolution Accurate Mass Spectrometry.

Naphthenic acids (NAs) are naturally occurring organic acids found in crude oils. NAs are one of the main classes of acids found in produced water (PW). In the petroleum industry, the need to stabilize oil-water emulsions leads to a demand for reliable methods for compositional analysis of these emulsions. Gas chromatography coupled to mass spectrometry (GC-MS) is one of the most important techniques for NA profiling. Traditional methods employ a derivatization step to improve the volatility and detectability of NAs. In this work, we propose a simple method for profiling free NAs in PW by GC-MS. Eight analytical columns were carefully selected by evaluating metrics, such as normalized analyte response and select chromatographic parameters. The best-performing columns were used to analyze NAs extracted from a real-world PW sample. The analytes were detected by Fourier-transform orbital ion trap mass spectrometry using chemical ionization in the negative mode (NCI). The combination of the selected columns and the enhanced signal-to-noise ratio (S/N) attained by the GC-NCI-high resolution, accurate-mass mass spectrometry (HRAM-MS) method made it possible to detect and identify several homologous series of acidic oxygenated compounds ranging from aliphatic to aromatic analytes. [ABSTRACT FROM AUTHOR]