Development of methods to collect and analyze gasoline range (C5–C12) hydrocarbons from seabed sediments as indicators of subsurface hydrocarbon generation and entrapment

Abstract

Abstract Gasoline range hydrocarbons (C 5 –C 12 ) are usually associated with petroleum generation, yet few surface geochemical surveys have attempted to evaluate the gasoline range hydrocarbons in near-surface marine sediments. This is due to the difficulty in capturing and analyzing this volatile range of hydrocarbons with minimum loss and evaporative fractionation. In this study, a Headspace Solid Phase Microextraction (HSPME) method was developed and evaluated for the purpose of capturing the gasoline range of hydrocarbons within unconsolidated sediment using a solventless protocol. The sediment SPME extraction method is based on the condition that phase/composition equilibrium is reached between sediment/water mix, container headspace, and SPME fiber coated with sorbent. In the experiments, the effectiveness of SPME to detect and measure low concentrations of migrated crude oil in marine sediments was evaluated. The following optimum laboratory procedure for SPME gasoline monitoring was established: collect the sample in sealed disrupter chamber (sealed sediment storage container which breaks apart sediment and releases interstitial volatile hydrocarbons), use a water bath to keep a stable laboratory temperature, use an NaCl saturated solution to help aromatic compounds move out of the solution to vapor phase, and wait a sufficient time to reach equilibrium. The results show that HSPME is very sensitive with sub ppm detection limits. SPME proved to be suitable to reveal the natural background and micro-seepage level of gasoline hydrocarbons in marine sediments.