In conclusion, Raman spectroscopy and liquid chromatography (IC and RP-HPLC) have turned out to be suitable complementary
techniques. In fact, in this case Raman spectroscopy has supported the identification of compounds since it was able to identify the salt (anionþcation), whereas IC has supported the quantification of the salt based on the ion concentration. Therefore, both tech- niques are appropriate to determine the ionic species from ex- plosive residues on handprints and fingerprints. In addition, RP- HPLC enabled the determination of EGDN in extracts from dyna- mite. As consequence of the different information provided by both techniques, we propose residues should be first identified by Raman spectroscopy (since Raman spectroscopy is more rapid in comparison to liquid chromatography) and, then, quantified by liquid chromatography, in the appropriate mode.
As future trend, it is important to mention that Raman spec- troscopy seems to allow the discrimination between salts even when they are composed by the same anion due to the effect of the counter cation. Thus, further studies are being performed considering a wider number of salts in order to confirm this cap- ability of Raman spectroscopy and research this phenomenon more thoroughly (i.e. how the cation shifts the anion band, the influence of charge and size of the cation, etc.).
Novelty statement
The use of confocal Raman spectroscopy in comparison to an- ion-exchange chromatography for the identification of explosives residues on handprints has been investigated, for the first time, in this research study. Black powder, smokeless gunpowder, dyna- mite and ammonium nitrate have been the explosive samples considered. The obtained results encourage the use of these both complementary techniques to properly identify and quantify in- organic explosives.
Conflicts of interest
The authors have declared not conflicts of interest.