FormNo. 203-821-244 01/05-REV0
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9
In another example (Table 7) where the soil extract had very high concentrations of PCBs, as
confirmed by GC-TOFMS, the biases for GC-ECD are evenmore striking (again highlighted in red).
Table7.
Comparison of GCxGC-ECD and parallel dual-column GC-ECD results (pg/µL) for a "real
world" soil extract.
Pesticide
GCxGC-ECD GC-ECD
Tetrachloro-m-xylene
2.06
1.52
alpha-HCH
ND
4.96
beta-HCH
ND
3.94
gamma-HCH
154
118
delta-HCH
ND
42.1
Heptachlor
28.1
13.1
Aldrin
26.4
70.0
Heptachlor epoxide
ND
42.2
gamma-Chlordane
3.26
ND
Endosulfan I
ND
ND
alpha-Chlordane
ND
99.4
Pesticide
GCxGC-ECD GC-ECD
Dieldrin
1.45
12.6
4,4’-DDE
124
199
Endrin
ND
216
Endosulfan II
ND
28.4
4,4’-DDD
ND
121
Endrin aldehyde
ND
49.1
Endosulfan sulfate
ND
ND
4,4’-DDT
70.9
480
Endrin ketone
ND
ND
Methoxychlor
60.4
ND
Decachlorobiphenyl
2.80
2.75
ND= not detected. This samplewas diluted 30:1 prior to analysis.
The reason for the less biased performance of GCxGC-ECD can be deduced from the contour plot
shown in Figure 6. The PCBs tend to elute in a relative straight line along the X-axis since they are
not as significantly retained on Rtx-200 as the pesticidesmarkedwith yellow ovals in the figure.
Moving the pesticides away from this chromatographic linewith the second dimension separation
leads to less chance of an erroneously high quantitation value for an OCP.
Pesticide
Rtx-5
Endrin
Endosulfan II
DDD
Endrin aldehyde
DDT
480
70.9
4,4’-DDT
ND
ND
ND
ND
GCxGC
28.4
Endosulfan II
Endrin aldehyde
4,4’-DDD
Endrin
49.1
121
216
GC
<<<PCBs>>>
Figure6.
Zoomed in
contour plot of a
"real world" soil
extract showing
PCBs eluting along a
relatively straight
line in the first
dimension. The
OCPs (with their
chromatographic
placesmarked by
yellow ovals), except
for DDT, aremoved
off of the X-axis by
the Rtx-200 column,
and are less prone to
interference (and
high quantitative
bias), as seen in the
inset table results.
