Naphthenic acids as indicators of crude oil biodegradation in soil, based on semi‐quantitative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Abstract

Crude oil contaminated soil cores were collected from a basin that contained oily solids left from three decades of oil production. Hydrocarbon biomarker analyses revealed that the soil extracts were moderately biodegraded compared with the non-degraded source oil. The degree of biodegradation also decreased with core depth (7 cm to 1 m). These data were correlated to compositional changes observed in acidic NSO-compounds that were selectively ionized and mass resolved by negative ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Among the NSO-compounds ionized, the increase in naphthenic acid concentration (e.g., acyclic and alicyclic carboxylic acids) best correlated with the increase in biodegradation (e.g., from non-degraded to moderately degraded) as determined by the hydrocarbon biomarker analyses. The most biodegraded surface extracts (7 cm) exhibited an 80% increase in the abundance of acids relative to the source oil. Use of an internal standard allowed the semi-quantitative determination of the total naphthenic acid concentration, which decreased significantly (P < 0.05) with soil depth. Furthermore, the shift to higher double bond equivalents (DBEs), from acyclic to alicyclic acids, indicated that the increase in acids in the soil extracts was predominantly due to biotic processes. This work demonstrates the potential of ESI FT-ICR MS as a semi-quantitative tool to monitor the production of naphthenic acids during crude oil biotransformation in the environment.

Comprehensive study of a heavy fuel oil spill : modeling and analytical approaches to understanding environmental weathering

“…samples. The detection of species not native to the parent HFO, most of which contain oxygen, agrees with previous studies [28] and is supported by results from ISA and bulk analyses.…”

“…While we cannot quantify the naphthenic acids in the present work, their increasing relative abundance with time is in agreement with observations of . [28] The nearly 10 fold increase in relative abundance of these species with environmental exposure supports their recalcitrance in natural systems.…”

“…[8] No such changes are evident ( Figure S3), suggesting that the observed decrease in N 1 content is due to the increase in more efficiently ionized O 2 species. [8,28] Because of their higher ionization efficiencies, oxygen-containing species are less sensitive to changes within other compound classes. O 2 species increase from ~5 to ~13% across our time series.…”

“…[18] Although FT-ICR-MS has been used extensively to examine petroleum and petroleum products [6,[18][19][20][21], refinery deposits [5,6,22,23]and changes due to various refinery operations [17,22,[24][25][26][27], its application to environmental petroleum samples and processes has been limited. [8,17,28,29] In 2007 Francisco Bay by GC and reported dramatic losses of low molecular weight compounds eluting before n-C 16, during the initial eleven weeks of weathering. Compound ratios indicative of evaporation/water washing, biodegradation, and photodegradation suggested that these processes were responsible for observed changes.…”

Evaluation of Quantitative Sulfur Speciation in Gas Oils by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Validation by Comprehensive Two-Dimensional Gas Chromatography

“…A linear response up to reasonable concentrations was achieved after the optimization of the external ion accumulation period. The potential use of ESI FT-ICR MS as a semiquantitative tool to monitor the production of naphthenic acids during crude oil biotransformation was also investigated [16], and the quantitation of ARN-type acids in whole crude oils has been reported [17].…”