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.
Forensic
laboratory backlogs are replete with suspected drug samples.
Shifting analysis toward the point of seizure would save significant
time and public funds. Moreover, a two-tiered identification strategy
for controlled substance testing that relies on two independent, discerning
methods could entirely circumvent the need for forensic laboratory
testing. To this end, we coupled Raman spectroscopy and paper spray
ionization mass spectrometry (PSI-MS) on a single instrumental platform.
Both methods are capable of ambient analysis with fieldable instruments,
yet Raman is often limited to bulk analysis. Critical to this work
is the development of a gold nanoparticle (AuNP)-embedded paper swab
to extend the capability of Raman spectroscopy to trace evidence via
surface-enhanced Raman scattering (SERS). Plasmonic papers are characterized
with respect to SERS signals and compatibility with PSI-MS analysis.
Proof-of-principle is established with the identification of five
representative drugs, and detection limits on the scale of 1–100
ng are achieved for both PSI-MS and SERS. The integrated SERS-PSI-MS
system achieved 99.8% accurate chemical identification in a blind
study consisting of 500 samples. Additionally, we demonstrate facile
discrimination of several JWH-018 isomers via SERS even when MS and
MS2 spectra are indistinguishable. Successful coupling
of SERS and PSI-MS to enable on-site chemical analysis by two independent
methods can potentially lead to a desirable paradigm shift in the
handling of drug evidence.
The complexity of field-borne sample matrices and the
instrumental
constraints of portable mass spectrometers (MS) often necessitate
that preparative steps are added prior to ambient MS methods when
operated on-site, but the corresponding decrease in throughput and
experimental simplicity can make field operation impractical. To this
end, we report a modified ambient MS method, filter cone spray ionization
(FCSI), specifically designed for simple, yet robust, processing of
bulk forensic evidence and environmental samples using a fieldable
MS system. This paper-crafted source utilizes low-cost laboratory
consumables to produce a conical structure that serves as a disposable,
spray-based ionization source. Integrated extraction and filtration
capabilities mitigate sample heterogeneity and carryover concerns
and expedite sample processing, as characterized through the analysis
of a variety of authentic forensic evidence types (e.g., abused pharma
tablets, counterfeit/adulterated tablets, crystal-based drugs, synthetic
marijuana, toxicological specimens) and contaminated soil samples.
The data presented herein suggests that the FCSI-MS design could prove
robust to the rigors of field-borne, bulk sample screening, overcoming
the inefficiencies of other ambient MS methods for these sample classes.
Novel applications of FCSI-MS are also examined, such as the coupling
to trace evidence vacuum filtration media.
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.
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