Forensic Department "Environment-Fire-Explosives"
Forensic Expert - Forensic Department "Environment-Fire-Explosives", IRCGN
Over the past decade, significant technological developments have led to increase the availability of high resolution mass spectrometer with improved capabilities: high sensitivity; high mass accuracy and resolution over a wide range mass. Therefore, the performance, the versatility of LC-HRMS and its widespread applications are nowadays well-known and used in most analytical chemistry areas including forensic laboratories.
A core task of any forensic laboratory is providing comprehensive information on the chemical composition of evidence.
Millions of natural and synthetic molecules are described in growing chemical structure database such as PubChem (94 millions) or Chemspider (63 millions). This vast, diverse universe of organic compounds constitutes a massive challenge for forensic chemists in charge of identification of any relevant compound present in an evidence. Non targeted screening (NTS) based on HRMS has promising potential to reach this goal in routine case work applying either data-dependent-acquisition (DDA) or data-independentacquisition (DIA).
In the absence of criminal specific context, no bodily unknown samples are, in some way, even more difficult to characterise due to the very opened window of research of compounds. HRMS database, where chemical fingerprints of molecules are stored, should be as exhaustive as possible in order to easily distinguish identifiable expected compounds from unexpected compounds.
To be elucidated, compounds must be first extracted from complex matrix and well detected which can involve the need of complementary detection techniques (GC-MS, NMR, MEB…). The confidence level of identification remains a key problematic for the unknown compounds since it is not always possible to purify traces or to hold/synthesize standards of unexpected molecules.
Furthermore, High Resolution Mass Spectrometry allows data profiling and retrospective data treatment which can be a true advantage for research investigations or legal issue in comparison of targeted analysis performed with low resolution instrument.
With all of these points in mind, a discussion focused on the identification of unknown nobodily compounds will be proposed. A quick review on current HRMS potentials and NTS features will be followed by a description of how we conceive them into our analytic strategy: sample preparation, analytical techniques cascade and equipment platform, homemade QToF databases (surfactants, lubricants, OGSR, fuel and food additives, NPS, dyes…), workflows and data mining, levels of confidence and expert control. To highlight the daily application of our forensic strategy, an interesting case will conclude the presentation.
Analytic Strategy, LC-HRMS, Untargeted Screening