Re-evaluation assessment of a large volume sampling (LVS) system for the determination of petroleum hydrocarbons and their stable carbon isotopes in deep-sea waters

Abstract

We have revisited the large volume sampling (LVS) technique and its analytical methodologies to develop and validate (step by step) a home-made solid-phase extraction (SPE) system (Amberlite® XAD-2 resin-based) connected to a particle collector in situ pump (McLane WTS-LV04) for high sample pre-concentration and determination of chemical contaminants (e.g. aliphatic and aromatic petroleum hydrocarbons) and their ¹³C/¹²C isotope ratio. The SPE laboratory extraction/elution procedure was newly adapted from the Bligh and Dyer method to facilitate the removal of the residual water derived from the sampling. The comprehensive sampling and analytical method was validated in the framework of a “top-down” single-laboratory approach using coastal seawater samples. In the dissolved phase of seawater, full quantitative validation was achieved for semi-volatile polycyclic aromatic hydrocarbons (PAHs; from naphthalene to methylpyrene) by gas chromatography mass spectrometry (GC-MS). The LVS approach was also validated for performing compound-specific stable ¹³C/¹²C ratio measurements by gas chromatography (combustion) isotope ratio mass spectrometry (GC-C-IRMS). Overall, both the long field sampling and analytical operational times, as well as the blank levels and interference from resins might restrict this LVS technique as a routine procedure for monitoring contaminants in seawater, but for research and non-routine measurements it will still be the state of the art to investigate and trace unknown chemical contaminants in deep sea marine environments.