Table 3. Comparison between GC-TID and GC-ECD
laboratory (Method 8095) results for explosives in
solvent extracts of archived soil samples collected
at military facilities. Sample extracts were analyzed
by both methods at the same time.
Analyte concentration (g/kg)
2,4-DNT
TNT
TID
ECD
TID
ECD
1.
140
130
47
47
2.
4.3
7.6
51
77
3.
290
300
290
320
4.
ND
ND
ND
1.1
5.
ND
0.8
0.8
1.7
6.
18
19
92
110
7.
7.5
8.8
0.7
0.7
8.
420
420
2.1
1.2
9.
9200
8000
28
32
10.
9.3
9.5
250
220
Median and range of the % differences for analysis pairs (ECD
reference value) with analyte concentrations.
2,4-DNT
TNT
Median
2.72
4.0
Range
43.4 to 15.0
33.8 to 75.0
of 10 cases) or values considerably higher (3, 3 out of
ing high levels of TNT or RDX, or both, by Methods
10) than the Method 8095 results. The GC-TID chro-
8510 and 8515. Several explosives analytes were de-
matograms that resulted in false positives or biased high
tected in these soil samples, as well as the archived sedi-
HMX concentrations often had a very broad peak for
ment samples and water sample extracts that were made
this explosive. This poor peak shape most likely is an
available for analysis. The most frequently detected
indication that background interferences were present.
analytes by GC-TID were 2,4-DNT, TNB, TNT, RDX,
One of the more interesting findings of this field trial
and HMX. Table 4 shows the values obtained by both
was that, while the GC-TID results agreed with the
GC-TID performed on site and GC-ECD (Method 8095)
Method 8515 results for TNT, more often than not they
subsequently obtained in our laboratory at CRREL for
did not agree with the Method 8510 results for RDX.
TNB, TNT, and RDX.
In those samples where Method 8510 obtained a re-
The results in Table 4 show good agreement (median
sponse for RDX that resulted in a concentration that
percent difference values of less than 13%) between the
was not confirmed by GC-TID analysis, the GC-TID
two methods of analysis for TNB, TNT, and RDX. The
chromatograms showed a peak(s) that eluted before 2,6-
reduction of TNT in the acetone extracts did not appear
DNT or just before RDX, or both. Analysis of these
to occur as it had for the samples returned from Fort
same sample extracts in the laboratory by both GC-
Leonard Wood. Perhaps TNT is more stable in acetone
ECD and GC-TID established that the peak appearing
at the higher concentrations typical of these samples,
before 2,6-DNT was NG while the peak on the front
or perhaps the storage condition (storage in a freezer
edge of the RDX peak was PETN. Both NG and PETN
versus on ice) used for these samples was better. 2,4-
are analytes that give a positive response when using
DNT was not included in this table because it was
Method 8510 (Crockett et al. 1996). Therefore, by us-
present only at concentrations below the lowest cali-
ing the GC-TID, these analytes and HMX, all of which
bration standard used during this field demonstration.
give a positive response by Method 8510, could be re-
A couple of problems were encountered with the GC-
solved.
TID estimates for HMX, i.e., false positives (three out
9
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