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