Combining a portable, tandem mass spectrometer with automated library searching – an important step towards streamlined, on-site identification of forensic evidence

Abstract

Ambient sampling, portable mass spectrometers have the potential to revolutionize forensic chemical analysis by allowing evidence screening to take place at the native locale, expediting criminal investigations and easing the burden on backlogged forensic laboratories. To evaluate the usability of such a system coupled with ambient ionization techniques, tandem MS spectra were obtained for a variety of forensically-relevant analytes and compared to an established reference library, the "Wiley Registry of Tandem Mass Spectral Data, MSforID" (Wiley Registry MS/MS), with an end goal of allowing automated chemical identification for non-technical user operation. Samples of interest included 25 positive controls, 4 negative controls, and 3 samples of authentic powder-based drug evidence. Of the 69 MS/MS spectra collected at varying collision-induced dissociation (CID) energies for the positive control samples, 68 of the spectra produced relative average match probabilities (ramp) values high enough to result in "true positive" identifications for all 25 samples tested. None of the negative control samples resulted in false-positive identifications when both obtained ramp values and visual comparison of spectra were considered. Of note, all powdered drug evidence samples examined were correctly identified by the commercial library, showing high promise for use in routine drug evidence screening.The ability for in-source fragmentation and structural isomers to produce false positive/negative responses was also investigated.

Analytical Validation of a Portable Mass Spectrometer Featuring Interchangeable, Ambient Ionization Sources for High Throughput Forensic Evidence Screening

“…As previously reported [24,26,44], this system features a capillary-based atmospheric pressure inlet for coupling to ambient ionization methods, while providing analyte confirmation via MS/MS. Cartridge-based helium CID damping gas, syringe pump solvent delivery, and the high voltage supply needed for all investigated ionization sources are incorporated into the instrumental design.…”

“…It has been asserted that the addition of the N-(2-methoxy)benzyl group to the 2C-phenethylamine structure (another electron donating aromatic ring, as seen in Supplementary Figure S-8C) creates more favorable sites for dissociation that can occur along the -C-C-N-C-linkage chain, specifically C-C bond cleavage between the α-and β-carbon atoms on the ethylene bridge [68,69]. The complexity and intensity to which these fragmentation patterns are seen is highly dependent on the MS/MS conditions utilized [44], which leads to the inter-instrument variations reported [66,70]. While NBOMe derivatives may represent a special case due to the number of low abundance transitions seen, instrument-specific spectral databases [71] may be more prudent in scenarios where automated chemical identification is needed, but variability is a concern.…”

“…Increases in the total ion count denote the usage of each ion source for a minimum of 30 s, and a return to baseline depicts the time required for source switching, coupling of solvent and voltage connections, and needed positioning. Overall, five distinct sample/source combinations were able to be processed in less than 6 min total, generating characteristic spectral data for each scenario, as seen in Figure 1b through f. Ambient MS data collected upon the FLIR AI-MS 1.2 commonly exhibits significant in-source fragmentation (i.e., inadvertent fragmentation prior to initiating MS/MS scan modes) [24,44], similar to other portable [61] and lab-scale MS instrumentation [62] capable of sampling externally-generated ions. This in-source fragmentation can be varied, but rarely eliminated, by manipulating ion optic potentials in the high pressure regions of the vacuum system (e.g., tube lens/skimmer assembly) [63] and minimizing thermal dissociation (e.g., inlet capillary temperature) [64].…”

“…Reported applications demonstrate the utility of specific ambient MS techniques in this arena, allowing the direct analysis of utilized surface swabs [24], trace residues [41], bulk evidence [42], and highly complex sample matrices [26,43]. Furthermore, implementing automated spectral library searching and chemical identification on said systems can alleviate the need for field-based data interpretation, allowing the use by nontechnical operators [44].…”

“…Incorporation of tandem MS data in analyte identification even allows discernment from complex matrices [26,43]. Previous work towards establishing spectral congruence and selectivity compared blind portable MS/MS data to a widely accepted reference library, the 'Wiley Registry of Tandem Mass Spectral Data, MSforID', returning the correct identification for over 30 forensic analytes and evidentiary samples [44]. While this shows selectivity towards traditional drugs of abuse, extension towards novel psychoactive substances (NPS) [28], particularly those that are structurally similar and even isomeric, must be assessed.…”