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QuEChERS Extraction of Oil Contaminated Seafood - PAHs

27 Jun 2010

“Growing up” as an environmental analytical chemist, I always think of hydrophobic contaminants, like Polycyclic Aromatic Hydrocarbons (or PAHs), needing hydrophobic solvents to isolate/extract them from hydrophobic matrices, like fish or seafood. (Dang, he’s using hydrophobic so much he must be rabid…) In fact, I’d seen reduced recoveries when trying to QuEChERS extract (with polar acetonitrile) PCBs and PBDEs from meat-based baby foods. So I’ve been skeptical that QuEChERS would work for extracting PAHs from seafood (an application that is necessary because of the recent Gulf oil spill), even though there is a paper published on using QuEChERS for PAHs in fish (Analysis of polycyclic aromatic hydrocarbons in fish: evaluation of a quick, easy, cheap, effective, rugged, and safe extraction method; J. Sep. Sci. 2009, 32, 3529 – 3538).

This weekend I gave it a try at 100 ng/g spike levels for scallops, shrimp, and oysters, and it worked surprisingly well. I paid close attention to trying to make sure my spike was intimate with my homogenized sample before extraction, and used aggressive vortexing for 15 min during acetonitrile extraction, and then again after EN 15662 buffer salts addition. I also used PTFE centrifuge tubes to minimize PAH losses to the extraction and dispersive SPE (dSPE) vessels. My dSPE cleanups were with 150mg MgSO4 + 50mg PSA + 50mg C18 per mL extract. While acetonitrile extracted relatively little lipids, it would still be enough to foul GC injectors and columns, so the C18 removed much of the lipids (e.g. scallops went from about 2.7 mg/mL “nonvolatile” residue before dSPE to about 0.34 mg/mL after C18 dSPE).

The QuEChERS approach may allow labs on a budget to avoid the use of expensive pressurized fluid extraction systems (like ASE) and solvent-intensive GPC cleanup (ala the NOAA Method) as they respond to seafood analyses for the oil spill. Time savings will be good with QuEChERS, also.

A fast GC-TOFMS run with a 15m x 0.25mm x 0.25µm Rxi-5Sil MS column allowed determination of the PAHs in less than 12 minutes at 50 pg/µL (the 100% recovery level) and less. This short column is much preferred over the 60m DB-5 suggested by the NOAA Method, for time savings and reduced cost and better sensitivity.

The table shows recoveries for select PAHs. Contact me for more specific details regarding the QuEChERS procedure, including sample amounts, water added, shaking times, GC and MS procedures, and recoveries for organochlorine and organophosphorus and organonitrogen pesticides, PCBs, aliphatic compounds, and other semivolatiles (that were spiked also).


table