Smokeless powders are explosives that are typically used as propellant for ammunition but are also encountered in improvised explosive devices such as pipe bomb. This is particularly true for the United States where smokeless powders are readily available [1]. While residue analysis is possible post-explosion, forensic experts often also encounter explosive devices pre-explosion. In such an explosion, investigators must establish a chemical profile of the propellant and compare it to the energetic material found elsewhere such as a suspect’s home.
Scientist Rick van den Hurk from the Chemometrics and Advanced Separations Team (CAST) at the van ‘t Hoff Institute for Molecular Sciences (HIMS) of the University of Amsterdam developed a method to simultaneously characterize smokeless powders both on molecular weight distribution and additive profile. For the method, Van den Hurk employed two-dimensional liquid chromatography (Figure 1). Combining organic size-exclusion chromatography and aqueous reversed-phase liquid chromatography, Van den Hurk designed a two-stage trapping system to improve compatibility and enhance sensitivity.
The size-exclusion chromatography (SEC) is conducted as first-dimension separation and resolves the smokeless powders based on size. Larger fragments will elute earlier than smaller fragments. An example is shown in Figure 2 on the left-hand side, with a comparison of two samples and their confidence intervals for the entire range.
Next, the additives, which are among the smallest molecules relative to the very large nitrocellulose molecules, are gathered by the trapping interface and injected into a second-dimension reversed-phase LC (RPLC) separation. An example of the additive package for three different smokeless powders is shown in Figure 2.
The project included contributions of students Anouk van Beurden and Mabel Dekker who co-developed the method within their internship project. Dekker examined the discrimination power of the SEC method, whereas van Beurden focused on the RPLC separation. Van Beurden also extensively investigated alternative methods to characterize the nitrocellulose in detail including the use of enzymatic degradation.
The project was conducted in collaboration with Annemieke Hulsbergen-van den Berg from the Dutch Forensics Institute (NFI), and investigated under the lead of Prof. Arian van Asten and Dr. Bob Pirok. Van Asten and Pirok together lead the PARADISE project along with Prof. Govert Somsen at the Vrije Universiteit of Amsterdam. The PARADISE project is a public-private funded collaboration between a consortium of industrial and academic partners. The project was funded by consortium members Covestro, DSM, Genentech, Shell, the Dutch Forensics Institute and the Dutch Science Council (NWO) and aims to advance the analysis of complex mixtures encountered in industry and society.
The work was published open-access in Journal of Chromatography A and can be freely downloaded here.
References
[1] K.D. Smith, B.R. McCord, W.A. MacCrehan, K. Mount, W.F. Rowe, J. Forensic Sci. 44, 1999, 14554J, DOI: 10.1520/jfs14554j
[2] R.S. van den Hurk, N. Abdulhussain, A.S.A. van Beurden, B.E. Dekker, A. Hulsbergen, R.A.H. Peters, B.W.J. Pirok, A.C. van Asten, J. Chromatogr. A, 1672, 2022, 463072, DOI: 10.1016/j.chroma.2022.463072