Supercritical fluid extraction applied to environmental pollutants from Chesapeake Bay sediment

Sample preparation via supercritical fluid extraction (SFE) has been increasingly used to determine polynuclear aromatic hydrocarbons (P AHs) in environmental samples. As an alternative sample preparation technique, SFE offers the distinct advantages of greatly reduced sample preparation time, concentrated analyte ready for assay, and comparable extraction efficiency to conventional liquid extraction. Supercritical carbon dioxide is the most widely used SFE fluid. Compared to the other supercritical fluids, carbon dioxide has several advantages: non-flammable, low cost, low toxicity, and low critical parameters.

Sixteen P AHs were extracted from dry Chesapeake bay marine sediment using two-step experimental conditions where step 1 was designed to extract the more volatile P AHs and used 100% CO2 and step 2 incorporated parameters for the removal and trapping of the less volatile P AHs with 10% acetone modified supercritical CO2. The final two-step extraction method arrived at exhibited no statistical difference from a previous interlaboratory round robin Soxhlet method on the same matrix in terms of P AH recovery. Recovery from dry marine sediment was compared with the recovery from wet marine sediment. The wet marine sediment was made from existing dry marine sediment by the addition of distilled water. Two methods were used to produce the wet matrix: (1) water added directly to the matrix in the extraction vessel and (2) water added to the matrix and mechanically homogenized. The presence of drying agent and the degree of water homogeneity in the wet matrix influenced the P AH recovery. Statistical analysis indicated that the level of water in the matrix had a significant effect on the recoveries of 13 out of 16 PAHs.

In addition, one-step extraction conditions were studied employing the same marine sediment on two different supercritical fluid extractors. However, one-step extraction conditions did not yield comparable results to those of the two-step procedure.

The final developed two-step extraction conditions were applied to the southern branch of the Elizabeth river sediment which had a high content of incurred elementary sulfur.