Simultaneous analysis of organic and inorganic explosive traces by online two-dimensional liquid chromatography

To investigate and process a crime scene after an explosion, analytical methods that can detect trace amounts of explosive material are essential. These chemical traces are of high chemical diversity, encompassing both inorganic and organic materials of forensic interest requiring different analytical techniques for characterization. In this work, we developed 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 developed. In the first dimension, hydrophilic interaction chromatography (HILIC) was applied for the separation of inorganic anions and cations. The use of active solvent modulation enabled transfer and refocusing of the organic fraction to a reversed-phase LC (RPLC) separation. The detection of ammonium was challenging using this analysis strategy. To enable sensitive detection of ammonium, a derivatization protocol was developed. The mobile phases of both separation dimensions are compatible with mass spectrometry, allowing for even more sensitive detection and selective, admissible identification. In this work, a combination of evaporative light scattering and ultraviolet absorption was used for detection of all the analytes. The developed HILIC – RPLC method was capable of analyzing different classes of explosives using a single method, reducing the required sample amounts and analysis time, thereby potentially enabling a faster, more efficient, and less work-intensive handling of explosive-related casework in forensic laboratories.