The components of explosive devices can be difficult to characterize, whether pre- or post-blast. To rectify this, two-dimensional liquid chromatography was tested as a means of analyzing these compounds.
To better characterize components in explosive devices, Dutch researchers, led by University of Amsterdam personnel, tested a new two-dimensional liquid chromatography (2D-LC)-based method of analyzing explosive traces. Their research was published in the Journal of Chromatography A (1).
As global terrorist attacks have persisted over the past decades, there have been pushes for further development of analytical strategies for explosive materials. A large part of these incidents was the use of improvised explosive devices (IEDs), which are constructed with a variety of products. While the composition of IED explosive charges can vary, they mostly consist of commercially available, "home-made,” or military organic substances with either nitro-, nitroxy-, or nitramine-groups, peroxides, or fuels mixed with inorganic salts comprising oxygen-containing groups. Explosives’ chemical compositions can vary depending on the production process, which render their determination highly relevant for tactical evidence and reconstruction.
The chemical diversity of post-blast explosive samples, in addition to required high sensitivity and unknown sample matrices, makes analysis challenging. This has led to multiple analytical approaches being required to scan samples for the presence of the full range of compounds of interest to forensic-explosive experts. One of the most common techniques used for determining organic explosives is reversed-phase liquid chromatography (RPLC) in combination with ultraviolet (UV) or mass spectrometric (MS) detection. For the trace analysis of inorganic ions, ion-exchange chromatography (IEC) is a widely applied technique for determining anionic or cationic analytes. However, this strategy has several disadvantages, including limited sample quantities being collected from crime scenes, different sample preparation procedures being required, and increased use of resources and equipment.
In this study, the scientists aimed to create a workflow that allows for the simultaneous separation and detection of inorganic anions, cations, and organic explosive materials from a single injection. A heart-cutting two-dimensional liquid chromatography (2D-LC) method was used in this process. In the first dimension, hydrophilic interaction chromatography (HILIC) was applied for the separation of inorganic anions and cations. Using active solvent modulation enabled the organic fraction to be transferred and refocused on in the second dimension, which involved reversed-phase LC (RPLC) separation.
To test this analysis strategy, the system was used to detect ammonium. To enable sensitive detection, a derivatization protocol was developed. The mobile phases of both separation dimensions were compatible with MS, allowing for notably sensitive detection and selective, admissible identification. Overall, a combination of evaporative light scattering and ultraviolet (UV) absorption was used to detect all the analytes, with UV spectra helping to distinguish between organic explosives.
Future work may implement MS detection into 1D HILIC to solve the problems of analyte identification and poor detection limits of technologies like evaporative light scattering detectors (ELSDs). However, this would involve MS having to switch between positive and negative mode rapidly as the inorganic analytes possess both charge states. Ultimately the scientists declared their 2D-LC method to be applicable to pre- and post-blast explosive materials that may be collected as physical evidence at crime scenes. Achieving this requires the investigation of different matrices’ influences in which explosive residues may be present at crime scenes. Tentatively using MS detection will be even more important for practically applying this separation method and identifying peaks, regardless of retention time or UV absorbance spectrum, before the method goes through validation.
(1) Hurk, R. S. v. d.; Belina, E.; Verduin, J.; et al. Simultaneous Analysis of Organic and Inorganic Explosive Traces by Online Two-Dimensional Liquid Chromatography. J. Chromatogr. A 2025, 1758, 466187. DOI:
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