Page 299 - Advances in Forensic Applications of Mass Spectrometry - Jehuda Yinon

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267.6

100 272.7 432.4
Relative abundance 60 107.8 177.7∗ 192.8 257.6∗ 262.6 277.8
80

40

20
0 97.8∗
50 100 150 200 250 300 350 400 450 500
m/z
Figure 6.24 Positive-ion ESI mass spectrum of Powermite, a slurry explosive,
o
at heated capillary temperature of 100 C. * cluster ions due to ammonium
nitrate, [(NH 4 NO 3 ) n NH 4 ] , n = 1,2,3; cluster ions due to sodium nitrate,
+
[(NaNO 3 ) n Na] , n = 1,2,3 (From Zhao, X. and Yinon, J., Forensic identification of
+
explosive oxidizers by electrospray ionization, Rap. Comm. Mass Spectrom., 16,
1137, 2002. © John Wiley & Sons Ltd. Reproduced with permission).
result from ion-molecule interactions between the two compounds. For
+
example, the ion at m/z 268 is probably due to [(NH NO ) (NaNO )Na] or
4
3
3 2
+
[(NH NO )(NaNO ) NH ] .
3
3 2
4
4
6.4 Summary and Future Directions
Liquid chromatography/mass spectrometry (LC/MS) has become a routine
analytical technique in many forensic laboratories.
LC/MS in the negative-ion mode has proven to be the method of choice
for trace analysis of most explosives. ESI was found to be most suitable for
nitramine explosives, while APCI is better suited for nitroaromatic com-
pounds. For nitrate esters, both ionization techniques are adequate. Best
results are obtained when using a postcolumn additive, which will result in
formation of abundant characteristic adduct ions. Lowest detection limits
are in the ppb range.
Without the use of an additive, various adduct ions will be formed,
mainly in nitramine and nitrate ester explosives, which will depend on the
impurities present in the system and in the solvent.
Future directions indicate more use of MS/MS techniques, in combina-
tion with LC/MS, for characterization of explosive residues.
The forensic community is now ready for a database of LC/MS chro-
matograms and mass spectra, which will be of great value to identify and
characterize explosive residues in bombing cases.

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