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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Per-and polyfluoroalkyl substances (PFAS), an emerging class of toxic anthropogenic chemicals persistent in the environment, are currently regulated at the low part-per-trillion level worldwide in drinking water. Quantification and screening of these compounds currently rely primarily on liquid chromatography hyphenated to mass spectrometry (LC-MS). The growing need for quicker and more robust analysis in routine monitoring has been, in many ways, spearheaded by the advent of direct ambient mass spectrometry (AMS) technologies. Direct analysis in real time (DART), a plasma-based ambient ionization technique that permits rapid automated analysis, effectively ionizes a broad range of compounds, including PFAS. This work evaluates the performance of DART-MS for the screening and quantification of PFAS of different chemical classes, employing a central composite design (CCD) to better understand the interactions of DART parameters on their ionization. Furthermore, in-source fragmentation of the model PFAS was investigated based on the DART parameters evaluated. Preconcentration of PFAS from water samples was achieved by solid phase microextraction (SPME), and extracts were analyzed using the optimized DART-MS conditions, which allowed obtaining linear dynamic ranges (LDRs) within 10 and 5000 ng/L and LOQs of 10, 25, and 50 ng/L for all analytes. Instrumental analysis was achieved in less than 20 s per sample.

Parallel extraction of headspace volatiles from multiwell plates using sorbent sheets (HS-SPMESH) followed by direct analysis in real-time high-resolution mass spectrometry (DART-HRMS) can be used as a rapid alternative to solid-phase micro-extraction (SPME) gas-chromatography mass-spectrometry (GC-MS) for trace level volatile analyses. However, an earlier validation study of SPMESH-DART-MS using 3-isobutyl-2-methoxypyrazine (IBMP) in grape juice showed poor correlation between SPMESH-DART-MS and a gold standard SPME-GC-MS around the compound’s odor detection threshold (<10 ng/kg) in grape juice, and lacked sufficient sensitivity to detect IBMP at this concentration in grape homogenate. In this work, we report on the development and validation of an improved SPMESH extraction approach that lowers the limit of detection (LOD < 0.5 ng/kg), and regulates crosstalk between wells (<0.5%) over a calibration range of 0.5–100 ng/kg. The optimized SPMESH-DART-MS method was validated using Cabernet Sauvignon and Merlot grape samples harvested from commercial vineyards in the central valley of California (n = 302) and achieved good correlation and agreement with SPME-GC-MS (R2 = 0.84) over the native range of IBMP (<0.5–20 ng/kg). Coupling of SPMESH to a lower resolution triple quadrupole (QqQ)-MS via a new JumpShot-HTS DART source also achieved low ng/kg detection limits, and throughput was improved through positioning stage optimizations which reduced time spent on intra-well SPMESH areas.

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