FormNo. 203-821-244 01/05-REV0
LECO is a registered trademark of LECO Corporation
8
In Table 5, GCxGC-ECD and GC-ECD results are compared for a "real world" water extract. To start
with, looking at the surrogate results (tetrachloro-m-xylene and decachlorobiphenyl) for each
method is a goodway to gauge the results. Asmight be expectedwithwater samples, which in
general are less complex and less subject to interferences versus soil samples, the numbers are in
good agreement.
Table5.
Comparison of GCxGC-ECD and parallel dual-column GC-ECD results (pg/µL) for a "real
world" water extract.
Pesticide
GCxGC-ECD GC-ECD
Tetrachloro-m-xylene
21.4
19.8
alpha-HCH
ND
ND
beta-HCH
10.5
8.91
gamma-HCH
49.9
39.0
delta-HCH
ND
ND
Heptachlor
39.2
31.1
Aldrin
21.7
21.5
Heptachlor epoxide
ND
ND
gamma-Chlordane
35.9
33.4
Endosulfan I
ND
ND
alpha-Chlordane
59.1
61.0
Pesticide
GCxGC-ECD GC-ECD
Dieldrin
13.9
10.1
4,4’-DDE
35.1
32.6
Endrin
61.0
54.2
Endosulfan II
ND
ND
4,4’-DDD
ND
ND
Endrin aldehyde
ND
ND
Endosulfan sulfate
36.4
31.5
4,4’-DDT
47.9
43.3
Endrin ketone
ND
ND
Methoxychlor
134
114
Decachlorobiphenyl
24.0
20.3
ND= not detected.
For "real world" soil extracts, differences start to show between GCxGC-ECD and parallel dual-
column GC-ECD results. In Table 6, highlighted in red are some of themore dramatic concentration
differentials seen for a soil extract. Especially note the highly biased value for gamma-HCHwith
GC-ECD. Based on gas chromatography–time-of-flight mass spectrometry (GC-TOFMS) analysis,
this samplewas seen to contain polychlorinated biphenyls (PCBs), and that is what is likely causing
the high gamma-HCH value for GC-ECD. Interestingly, neither column used in the parallel dual-
columnwork (Rtx-CLPesticides and Rtx-CLPesticidesII) provided an unbiased gamma-HCH
concentration.
Table6.
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
31.8
25.9
alpha-HCH
ND
15.9
beta-HCH
ND
ND
gamma-HCH
ND
64.9
delta-HCH
ND
9.19
Heptachlor
1.44
ND
Aldrin
ND
ND
Heptachlor epoxide
20.3
10.3
gamma-Chlordane
78.5
57.6
Endosulfan I
ND
ND
alpha-Chlordane
68.3
66.3
Pesticide
GCxGC-ECD GC-ECD
Dieldrin
10.8
6.92
4,4’-DDE
30.8
20.2
Endrin
0.27
27.8
Endosulfan II
ND
ND
4,4’-DDD
60.4
22.1
Endrin aldehyde
ND
5.18
Endosulfan sulfate
ND
ND
4,4’-DDT
211
145
Endrin ketone
ND
12.7
Methoxychlor
11.8
ND
Decachlorobiphenyl
35.9
34.2
ND= not detected.
