Optimization of methodology for the analysis of hydrocarbons in lagunar sediments

Abstract

Hydrocarbons are listed as some of the major environmental contaminants today and are considered geochemical indicators in relation to levels and sources of contamination in water environments. For this reason, there are standardized methodologies for the determination of these contaminants in sediments, among the most used, we can list the method of extraction by soxhlet and the method of extraction under ultrasound, but the two methods of extraction have disadvantages in their use. In this study, a methodology was developed for the extraction, preconcentration and clean up of hydrocarbons present in sediment, combining solvent extraction steps under ultrasound and soxhlet, followed by preparative liquid column fractionation and the extracts analyzed by gas chromatography coupled to mass spectrometry. For optimization, a 2² experimental design with central point evaluating the times of pre-sonification and soxhlet extraction was used. The method that presented the best results, combined 15 minutes of ultrasound and 4 hours of soxhlet, with average recoveries of 102.2% for deuterated PAHs (hydrocarbons polycyclic aromatic) and 100.2% for hexadecene, producing a reduction of time and volume of solvents, generating a reproducible method (RSD% <20%), fast and inexpensive. Detection limits for n-alkanes ranged from 0.9 to 13.9 μg kg^-1 and for PAHs from 0.11 to 0.93 μg kg^-1. The methodology was applied to samples of Pontal Beach, which is part of Mirim Lagoon, which is one of the main water bodies in the southern region of Brazil and is of great importance for agriculture, industry and livestock. PAHs and n-alkane levels indicated low levels of contamination and sources of biogenic and pyrolytic origin.