Evaluation of clean-up agents for total petroleum hydrocarbon analysis in biota and sediments

Petroleum hydrocarbons (oil) are common environmental contaminants. For risk assessment purposes, their concentrations in environmental matrixes, such as biota and soils/sediments are frequently determined by solvent extraction and subsequent analysis with gas chromatography (GC) equipped with flame ionization detection (FID) or mass spectrometry (MS). Because the total GC detector response is labeled as total petroleum hydrocarbon (TPH) concentration and matrix compounds (lipids, organic matter) will contribute to this response, proper extract clean-up is crucial. Still, the choice for a specific clean-up material during open column chromatography often seems arbitrary, since no comparative study on clean-up agents for TPH analysis is available. Here, such a study is described and it is demonstrated that none of the commonly used agents fulfills the requirements of complete matrix compound removal and TPH recovery. A novel column filled with (top-down) 1 g of 33% (w/w) 1 M NaOH-impregnated and 2.2 g of 7% (w/w) H2SO4-impregnated silica gel is recommended for cleaning-up biota extracts, as it fully removes extracted lipids and yields acceptable TPH recoveries of around 90%, based on a certified oil reference standard. For sediment extracts, most columns tested resulted in a negligibly low contribution of matrix compounds to the overall detector response, but 5% deactivated Florisil or 10% deactivated aluminum oxide are preferable, because these materials yield the highest (∼95%) TPH recoveries.