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Novel Approach for PAHs in Seafood:
Reduce Sample Prep fromDays to Hours Using QuEChERS and GCxGC
By Jack Cochran, Director of New Business and Technology
Consumer safety concern in the wake of the Deepwater Horizon oil spill has increased demand
for rapid, accurate test methods for polycyclic aromatic hydrocarbons (PAHs) in seafood. The
FDA has issued a protocol to reopen closed fishing waters that includes chemical testing of
seafood for PAHs, but the NOAA sample preparation method that was proposed is extremely
tedious and time-consuming, requires expensive pressurized fluid extraction and gel perme-
ation chromatography equipment, and uses large volumes of environmentally-unfriendly
methylene chloride. Alternative methods are being explored, and initial results for a novel
approach that combines a rapid QuEChERS extraction with the accuracy of GCxGC-TOFMS are
presented here.
QuEChERS Saves Time and Money
While QuEChERS was originally developed to simplify extraction and cleanup of pesticide
residues in fruits and vegetables, it is rapidly expanding to other applications due to its speed,
simplicity, and cost-effectiveness, so it was natural to consider it as a replacement for the NOAA
method. For this work, samples of freeze-dried mussel tissue containing NIST certified levels of
PAHs were prepared in less than 2 hours using a simple procedure that was quicker, easier, and
more cost-effective than the NOAA method (Figure 1).
GCxGC with Rxi®-17Sil MS and Rxi®-1ms Columns Ensures
Unbiased Separation of Key PAHs
Mussel samples were too complex for traditional GC/MS analysis, so GCxGC was employed. The
key to maximizing separations between peaks with this technique is to choose columns that
differ significantly in phase chemistry. An Rxi®-17Sil MS column was chosen for the first separa-
tion, as it is optimized for PAH separations (see article on p. 2), and a standard Rxi®-1ms column
was used for the second dimension to separate interfering fatty acids and sterols from the PAHs
of interest.
• Prepare samples in hours vs. days, using QuEChERS instead of
the NOAA method.
• GCxGC analysis minimizes matrix interference, for accurate
trace-level results.
• Selectivity of Rxi®-17Sil MS column assures separation of
benzofluoranthenes.
Figure 1 QuEChERS extraction and
cleanup procedure.
Note: Dried sample was used here; for fresh
samples, start at Step 3.
1. Weigh 1.0 g of NIST SRM 2974a tissue into
a 50 mL FEP centrifuge tube and add 10 mL
organic-free water. Shake 1 min. to wet
sample.
2. Aggressively vortex the sample for 15 min.,
then allow sample to settle for 30 min.
3. Add 10 mL acetonitrile and 20 µL of 25 ng/µL
Semivolatiles Internal Standard Mix (diluted
from cat.# 31206).
4. Shake sample by hand for 1 min., then
vortex for 15 min.
5. Add 1 packet of Q110 EN 15662 QuEChERS
extraction salts (cat.# 26236) and shake
hard.
6. Aggressively vortex the sample for 15 min.,
then centrifuge at 3,000 g for 5 min.
7. Transfer 1mL supernatant extract to a 10
mL FEP tube with 150 mg MgSO4 and 50 mg
PSA, and 50 mg C18 and shake 1 min. to
remove some fatty acids and lipids.
8. Centrifuge at 3,000 g for 5 min.
9. Withdraw extract for GCxGC-TOFMS analysis
of PAHs.
Example time savings:
Estimated processing time
for 30 fresh samples
QuEChERS: 10 hours
NOAA: 3-5 days
Food Safety
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