Abstract. Forensic evidentiary backlogs are indicative of the growing need for costeffective, high-throughput instrumental methods. One such emerging technology that shows high promise in meeting this demand while also allowing on-site forensic investigation is portable mass spectrometric (MS) instrumentation, particularly that which enables the coupling to ambient ionization techniques. While the benefits of rapid, on-site screening of contraband can be anticipated, the inherent legal implications of field-collected data necessitates that the analytical performance of technology employed be commensurate with accepted techniques. To this end, comprehensive analytical validation studies are required before broad incorporation by forensic practitioners can be considered, and are the focus of this work. Pertinent performance characteristics such as throughput, selectivity, accuracy/precision, method robustness, and ruggedness have been investigated. Reliability in the form of false positive/negative response rates is also assessed, examining the effect of variables such as user training and experience level. To provide flexibility toward broad chemical evidence analysis, a suite of rapidly-interchangeable ion sources has been developed and characterized through the analysis of common illicit chemicals and emerging threats like substituted phenethylamines.

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.

Ambient sampling, portable MS systems have the potential to allow field processing of forensic evidence, as well as serve as a flexible investigative tool during law enforcement activities. However, the underlying legal implications require the discretion of practitioners to ensure both lawful and ethical usage.

Portable mass spectrometers (MS) are becoming more prevalent due to improved instrumentation, commercialization, and the robustness of new ionization methodologies. To increase utility towards diverse field-based applications, there is an inherent need for rugged ionization source platforms that are simple, yet robust towards analytical scenarios that may arise. Ambient ionization methodologies have evolved to target specific real-world problems and fulfill requirements of the analysis at hand. Ambient ionization techniques continue to advance towards higher performance, with specific sources showing variable proficiency depending on application area. To realize the full potential and applicability of ambient ionization methods, a selection of sources may be more prudent, showing a need for a low-cost, flexible ionization source platform. This manuscript describes a centralized system that was developed for portable MS systems that incorporates modular, rapidly-interchangeable ionization sources comprised of low-cost, commercially-available parts. Herein, design considerations are reported for a suite of ambient ionization sources that can be crafted with minimal machining or customization. Representative spectral data is included to demonstrate applicability towards field processing of forensic evidence. While this platform is demonstrated on portable instrumentation, retrofitting to lab-scale MS systems is anticipated.

In this paper, an ambient sampling, portable mass spectrometer coupled to a selection on ambient ionization methods was used to perform real-time reaction monitoring of clandestine methamphetamine syntheses.

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Desomorphine is a semisynthetic opioid that is responsible for the psychoactive effects of a dangerous homemade injectable mixture that goes by street name "Krokodil." Desorption electrospray ionization (DESI) and paper spray ionization (PSI) are implemented on a portable mass spectrometer for the direct analysis of desomorphine and precursor reagent codeine from multiple substrates of potential relevance to clandestine drug laboratory synthesis and paraphernalia seizure. Minimal sample preparation required for analysis and portability of the instrument suggest the potential for rapid, on-site analysis of evidence, a highly desired benefit for forensic science and law enforcement practitioners. Both DESI-MS and PSI-MS can generate spectra consistent with preceding data obtained using traditional ionization methods, while demonstrating detection limits in the low-to sub-ng levels.

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