SLIM Ion Mobility-Based Analysis of Low Molecular Weight Explosives

The detection and differentiation of explosive compounds remain critical components of security applications and forensic work due to the potential complexity of samples and presence of isomeric compounds. Standalone ion mobility spectrometry (IMS) has been used in security screening for decades, useful for its ability to rapidly separate gas-phase ions based on differences in their size, shape, and charge. More recently developed high-resolution ion mobility-mass spectrometry (HRIM-MS) methods incorporate higher resolving power with accurate mass measurements to provide improved isomer separations and identification of unknowns. This work utilizes a novel Structures for Lossless Ion Manipulations (SLIM) ion mobility platform featuring a rounded turn design, which enhances the transmission of low-mass explosive compounds using helium buffer gas. Using negative mode atmospheric pressure chemical ionization (APCI), we demonstrate separation of isomeric nitroaromatic compounds such as 2,4- vs 2,6-dinitrotoluene (2,4-/2,6-DNT) and 2-amino-4,6- vs 4-amino-2,6-DNT. The rounded turn SLIM design significantly improved ion transmission efficiency over the traditional 90° turn system, especially for these low m/z analytes. With this, we demonstrate the ability of SLIM HRIM-MS to combine mobility separations, accurate mass, and isotopic patterns for improved separation and identification of isomeric explosives.