Fourier transform ion cyclotron resonance mass spectrometric analysis of NSO-compounds generated in hydrothermally altered sediments from the Escanaba Trough, northeastern Pacific Ocean

Abstract To date little is known about the functionalized and heteroatomic compounds present in hydrothermal petroleum and how these compounds are affected by high temperature vent fluids. To address this, the maltene fractions of three hydrothermal petroleum samples spanning the shallow depth of a sediment core collected in the Escanaba Trough of the Gorda Ridge in the northeast Pacific were analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in both negative electrospray ionization (ESI) and negative atmospheric pressure photoionization (APPI) ionization modes. These polar compounds were structurally similar to asphaltenes, but did not exceed a nominal mass range of ∼800 Da. They were derived primarily from terrestrially sourced organic matter (OM) with common heteroatom arrangements of CaHbOc, CaHbOcNd, CaHbNd, CaHbOcSe, CaHbOcNdSe, CaHbNdSe, and CaHbSe. The samples included compounds containing up to 19 oxygen heteroatoms and ranged in size from 10 to 53 carbon atoms with double bond equivalent (DBE) values of 1–38. Molecular formulae with N and S heteroatoms were minor. Within this sulfidic environment the formation and preservation of sulfur heterocyclic compounds was very low, which could be due to sulfurization being out-competed by the high concentrations of metals in the vent fluids or as a result of the thermal instability of C–S bonds. The dominance of oxygenated, and not thiolated, compounds was primarily source-dependent with secondary alteration by aromatization in this system proceeding by H abstraction and reduction of sulfate to H2S. We identified differences in the distributions of heteroatomic compounds caused by the expulsion, thermochemical oxidation, and differentiation of petroleum products during the migration of fluids to the sediment–water interface.