Analytical characterization of bulk R-Salt and its odor profile to establish a framework for canine detection

Abstract

In early 2025, an improvised explosive known as R-Salt (hexahydro-1,3,5-trinitroso-1,3,5-triazine), was recovered from multiple improvised explosive devices in a terrorist attack in New Orleans, USA. R-Salt is not commonly included in canine training kits and its odor profile has not yet been characterized, potentially affecting its detection by explosives detector canines (EDCs) in operational settings. This study provides an in-depth characterization of the headspace composition of R-Salt using thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) to provide methodology for future canine (K9) training aid development and evaluation. This work includes thorough characterization of the crude and recrystallized bulk material as well as methodical optimization of TD parameters, flow rates, and sample collection time used for headspace analysis. The odor profile of a laboratory grade batch of R-Salt before (R-Salt-C) and after recrystallization (R-Salt-R) was characterized at room temperature for comparison and to establish a baseline odor profile. The odor profile of R-Salt-R included two compounds, R-Salt and a potential degradant, while the R-Salt-C contained an additional 7 compounds, one of which is attributed to NO₂ off-gassing. In addition, the vapor pressure was determined to be 6.51 × 10⁸ atm for R-Salt-R using thermal gravimetric analysis whereas the vapor pressure of R-Salt-C was 3.15 × 10⁻⁷ atm, indicating the presence of additional volatile contaminants. The extensive characterization provided in this study can be used to evaluate EDC detection of R-Salt and the methodology can be utilized across the explosive forensics community for R-Salt headspace characterization, evaluation and development of K9 training aids.