One Step Ultrasound Extraction and Purification Method for the Gas Chromatographic Analysis of Hydrocarbons from Marine Sediments: Application to the Monitoring of Italian Coasts

In this study, we describe the development of an ultrasound-assisted method for the simultaneous extraction and purification of hydrocarbons from marine sediments and then its application to the gas chromatographic analysis for the estimation of the biogenic anthropogenic and petrogenic sources of hydrocarbons present in marine sediments. The extraction of hydrocarbons and their simultaneous purification from other organic compounds present in sediments was performed by sonication of a three phase system consisting of sediment, hexane and a HCl medium at pH 2. This method allowed accurate recoveries of the hydrocarbon content in samples. In the following GC-FID analysis, we examined the hydrocarbon distribution in four different areas of the Italian seas determining the pristane to phytane ratio, the total odd n-alkanes to even n-alkanes ratio (carbon preference index), the low molecular weight to high molecular weight ratio, perylene content and the presence of the so called unresolved complex mixture; according to recent studies, these parameters support the identification of the biogenic, anthropogenic and petrogenic hydrocarbon sources present in environmental samples. GC chromatograms were then re-examined by means of two different statistical multivariate methods: two-dimensional mapping (2DMAP) and independent component analysis (ICA). 2DMAP showed the presence of a significant heterogeneity in the hydrocarbon composition of different areas and within samples of a same area. ICA confirmed the general heterogeneity evidenced by 2DMAP allowing in addition to characterise the hydrocarbon composition of one of the investigated areas.