Forensic applications of DART-MS: A review of recent literature

Rapid Determination of 15 Herbicides in Blood and Soil by Direct Analysis in Real Time-Tandem Mass Spectrometry

RATIONALE

The rampant abuse of herbicides in agricultural practices has resulted in frequent incidents of both unintended and deliberate poisoning, posing dual threats to ecosystems and human health. This underscores an urgent need for efficient herbicide detection methods.

METHODS

A direct analysis in real time coupled with tandem mass spectrometry (DART-MS/MS) method was developed for the simultaneous detection of 15 herbicides in blood and soil. Systematic optimization of mass spectrometric parameters established optimal detection conditions in multiple reaction monitoring (MRM) mode, with the ion source temperature set at 450°C. Following liquid-liquid extraction of blood or soil samples, the processed supernatant was analyzed directly.

RESULTS

The method demonstrated excellent linearity (R² ≥ 0.99) across a wide concentration range. Sensitivity was validated with limits of detection (LODs) of 1-20 ng/mL in blood and 1-10 ng/g in soil, and limits of quantification (LOQs) of 1-50 ng/mL in blood and 1-20 ng/g in soil. Satisfactory recovery rates and controlled matrix effects met toxicological requirements. In 2024, the method was successfully applied to four real cases of herbicide poisoning.

CONCLUSIONS

This study established the first DART-MS/MS method for simultaneous analysis of 15 herbicides in biological (blood) and environmental (soil) matrices. The complete analytical workflow required only 20 minutes from sample preparation to detection, significantly advancing forensic applications of DART-MS/MSwhile providing a reliable technical solution for herbicide screening in forensic investigations.

Rapid Assessment of Samples from Large-Scale Clandestine Synthetic Drug Laboratories by Soft Ionization by Chemical Reaction in Transfer-High-Resolution Mass Spectrometry

The worldwide ongoing trend of synthetic drug production is also of increasing concern due to enormous amounts of chemical waste produced in clandestine laboratories. Typically, several tons of different types of production waste are stored in numerous containers and need to be characterized after dismantling a laboratory to assess production features, e.g., synthesis route and production scale, and to draw conclusions on the minimum number of batches produced. This forensic assessment is commonly done by a rather laborious gas chromatography - mass spectrometry approach. The aim of this work is to evaluate the suitability of the SICRIT (soft ionization by chemical reaction in transfer) ion source, which is based on the dielectric barrier discharge ionization principle, combined with high-resolution mass spectrometry (HRMS), for the rapid classification of liquid samples from amphetamine production in a seized large-scale clandestine drug laboratory. Among the different sample introduction methods tested, headspace analysis directly into the SICRIT ion source in conjunction with a heated inlet proved to be optimal. Identification of expected target substances (reaction educts, intermediates, byproducts, products) was possible as well as grouping related samples and assigning them to specific synthesis steps by multivariate data analysis in an unsupervised approach. In addition, supervised machine learning algorithms were evaluated to obtain a classification model for the assessment of production waste samples from one dismantled synthetic drug laboratory, and a random forest classifier showed the best performance with an accuracy of 97%. The potential of the novel SICRIT-HRMS approach for the assessment of synthetic drug laboratories was demonstrated.

A point-of-need framework for illicit drug identification with high-resolution mass spectrometry

The continually evolving drug landscape, with novel synthetic drugs and unique compositions, necessitates the need to advance technologies, data analysis methods, and data accessibility for compound detection and identification. Providing public health, first responder, and law enforcement communities with critical information in near real-time will aid emergency response and public awareness, and direct overdose prevention and interdiction efforts. A major component of this framework is the progression of accurate drug screening and preliminary identifications from a more rigid laboratory-based arrangement to an agile point-of-need paradigm. We investigated drug detection and identification of a field deployable ruggedized high-resolution time-of-flight mass spectrometer, employing both acetone-assisted vacuum ultraviolet (VUV) photoionization and dielectric barrier discharge ionization (DBDI) schemes. This preliminary fit-for-purpose exploration was conducted under laboratory conditions, considering ion sources not reliant on helium gas or external roughing pumps, building toward deployment in a mobile laboratory setting. The chromatography-free measurements enabled rapid analysis of neat drug solutions and multi-component mixtures. Characterization and optimization of system parameters demonstrated sensitive performance, with limits of detection in the tens to hundreds of picograms for a range of drug classes from multiple-component mixtures. The system's high mass resolution was calibrated with a polyethylene glycol calibrant, enabling accurate matching with spectral library entries. Integrating compound identification with the NIST DART-MS Forensics Database and NIST/NIJ DART-MS Data Interpretation Tool provided a solid foundation for transition to the point-of-need. The overarching framework seeks to support technology advancement and adoption, as well as the development of novel data analysis tools, processes, and management for public access and utilization.

Evaluating the capabilities of DART-MS compared to FTIR spectroscopy and SEM-EDS for the analysis of architectural paint mixtures

Architectural paint is a type of transferred trace material typically encountered by forensic laboratories, mostly in cases of forced entry. Forensic analysis of architectural paint generally consists of bright field microscopy followed by Fourier transform infrared (FTIR) spectroscopy. Further characterization can be achieved using additional techniques such as scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), Raman spectroscopy, and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). This study aimed to evaluate the effectiveness of DART-MS compared to FTIR spectroscopy and SEM-EDS for the analysis of architectural paint analysis, as well as investigate how DART-MS could be incorporated into a paint analysis workflow. A total of 45 architectural mixed paint samples were obtained by preparing combinations of five base color paints as binary mixtures in known proportions. DART-MS detected multiple organic compounds, including tributyl citrate (TBC), polyethylene glycol (PEG), dioctyl maleate (DOM), and tert-butyldiethanolamine (TBDEA) which are common plasticizers, additives, and solvents in architectural paints. DART-MS also showed the ability to identify the black paint in mixed paints above 10 % at both 350 °C and 500 °C, unlike FTIR and SEM-EDS. Meanwhile, FTIR spectroscopy identified several organic and inorganic compounds in each of the base color paints, including binders, pigments, and extenders, and was generally able to determine which base color paints were present in a mixture. In addition to supporting the identification of the inorganic compounds detected using FTIR, SEM-EDS also demonstrated greater sensitivity for small concentrations of inorganic compounds in the mixed paints. Overall, the compounds detected through DART-MS analysis were not found with either FTIR or SEM-EDS, highlighting the complementary nature of these techniques. Furthermore, DART-MS demonstrated the capability to identify and monitor ions specific to the black base paint within mixed paint samples, supporting the adoption of a combined approach for enhanced architectural paint discrimination.

DART isotope dilution high resolution mass spectrometry and 19F-NMR detection of fluorotelomeric alcohols in hydrolyzed food contact paper

Fluorotelomer-based acrylate polymers and surfactants used to grease-proof food contact paper (FCP) are potential sources of dietary exposure to perfluoroalkyl substances (PFAS). Food contact substances (FCS) containing polyfluorinated long-chains (≥C8) were voluntarily removed by their manufacturers from the U.S. market in 2011 due to health concerns and largely replaced with FCSs containing short-chain (≤C7) PFAS. In 2020, FDA findings of potential biopersistence of 6:2 FTOH (CF3(CF2)5CH2CH2OH) similarly prompted an additional voluntarily phase-out of FCSs containing 6:2 FTOH by their manufacturers that was completed by the end of 2023. To monitor the phase-out process, a screening method was developed to detect FCPs containing ester-linked polyfluorinated pendant chains. Direct Analysis in Real Time-Isotope Dilution-High Resolution Mass Spectrometry (DART-ID-HRMS) enabled rapid semi-quantitative detection of 6:2 FTOH in FCP saponification reaction headspace without requiring sample concentration or chromatography. 19F-NMR analysis confirmed 6:2 FTOH pendant chain identity and detection dependence on saponification. The speed and specificity of this approach arise from ester saponification in the presence of stable isotopically labeled 6:2 FTOH; high FTOH differential volatility relative to nonfluorinated matrix, and the facile production of FTOH gas-phase anions (e.g., [M + O2]·-, [M-H + CO2]-) under ambient ionization conditions. The efficiency of this simple workflow makes it well-suited for monitoring the phase-out of FCS containing ester-linked polyfluorinated chains from the U.S. marketplace.

A strategy for the detection of benzodiazepine drugs using low-resolution paper-spray mass spectrometry for harm reduction drug checking

The ability to detect newly emerging substances is of great importance in reducing harms for people who use drugs. New psychoactive substances including novel benzodiazepines in the illicit drug supply have been linked to high rates of overdose deaths while complicating drug checking as an overdose prevention strategy. Paper-spray mass spectrometry (PS-MS) has emerged as a novel strategy to rapidly detect trace components in street drug samples. While targeted, low-resolution PS-MS methods have proven effective, newly emerging substances are often missed. To address this, a method was applied to low-resolution full-scan PS-MS data to aid in the early detection and identification of novel benzodiazepines in the unregulated drug supply. Using the developed method, true positives rates of 0.89 and 0.75 were achieved for bromazolam and etizolam in street samples obtained in a community drug checking service. The applicability of the method was further demonstrated for a novel benzodiazepine, desalkylgidazepam, that has recently emerged in the illicit drug supply.

In-Line Thermal Desorption and Dielectric Barrier Discharge Ionization for Rapid Mass Spectrometry Detection of Explosives

Thermal desorption (TD) of wipe-based samples was coupled with an in-line dielectric barrier discharge ionization (DBDI) source and rugged compact time-of-flight mass spectrometer (MS) for the detection of explosives, propellants, and postblast debris. The chromatography-free TD-DBDI-MS platform enabled rapid and sensitive detection of organic nitramine, nitrate ester, and nitroaromatic explosives as well as black powder and black powder substitute propellants. Parametric investigations characterized the response to TD temperature and optimized DBDI voltage, aerodynamically assisted entrainment, and fragmentation through in-source collision induced dissociation (isCID). Excess nitrate generated by the DBDI source yielded predominantly nitrate-adduct formation. Subnanogram sensitivities were demonstrated for all explosives investigated, except for nitroglycerin, specifically due to its volatility. Further, most analytes/explosives exhibited tens of picograms sensitivities. The platform also demonstrated the detection of propellant and military explosives from postblast debris. The TD-DBDI-MS system performed well without the need for aerodynamically assisted entrainment (and the associated rough pump), which along with requiring no additional gases (i.e., N2 or He) or solvents, aid in potential field deployment. The ease of TD-DBDI attachment and removal added trace solid or liquid residue detection to the rugged mass spectrometer, designed primarily for the analysis of volatile organic and inorganic compounds.

An Agile and Accurate Approach for N-Nitrosamines Detection and Quantification in Medicines by DART-MS

N-nitrosamines (NAs) are prevalent mutagenic impurities in various consumer products. Their discovery in valsartan-containing medicines in 2018 prompted global regulatory agencies to set guidelines on their presence and permissible levels in pharmaceuticals. In order to determine the NAs content in medicines, efficient and sensitive analytical methods have been developed based on mass spectrometry techniques. Direct analysis in real time-mass spectrometry (DART-MS) has emerged as a prominent ambient ionization technique for pharmaceutical analysis due to its high-throughput capability, simplicity, and minimal sample preparation requirements. Thus, in this study DART-MS was evaluated for the screening and quantification of NAs in medicines. DART-MS analyses were conducted in positive ion mode, for both direct tablet analysis and solution analysis. The analytical performance was evaluated regarding linearity, precision, accuracy, limits of detection, and quantification. The DART-MS proved to be suitable for the determination of NAs in medicines, whether through direct tablet analysis or solution analysis. The analytical performance demonstrated linearity in the range from 1.00 to 200.00 ng mL-1, limits of quantification about 1.00 ng mL-1, precision and accuracy lower than 15%, and no significant matrix effect for six drug-related NAs. In conclusion, the DART-MS technique demonstrated to be an alternative method to determine NAs in medicines, aligning with the principles of green chemistry.

Tidy-Direct-to-MS: An Open-Source Data-Processing Pipeline for Direct Mass Spectrometry-Based Metabolomics Experiments

Direct-to-Mass Spectrometry and ambient ionization techniques can be used for biochemical fingerprinting in a fast way. Data processing is typically accomplished with vendor-provided software tools. Here, a novel, open-source functionality, entitled Tidy-Direct-to-MS, was developed for data processing of direct-to-MS data sets. It allows for fast and user-friendly processing using different modules for optional sample position detection and separation, mass-to-charge ratio drift detection and correction, consensus spectra calculation, and bracketing across sample positions as well as feature abundance calculation. The tool also provides functionality for the automated comparison of different sets of parameters, thereby assisting the user in the complex task of finding an optimal combination to maximize the total number of detected features while also checking for the detection of user-provided reference features. In addition, Tidy-Direct-to-MS has the capability for data quality review and subsequent data analysis, thereby simplifying the workflow of untargeted ambient MS-based metabolomics studies. Tidy-Direct-to-MS is implemented in the Python programming language as part of the TidyMS library and can thus be easily extended. Capabilities of Tidy-Direct-to-MS are showcased in a data set acquired in a marine metabolomics study reported in MetaboLights (MTBLS1198) using a transmission mode Direct Analysis in Real Time-Mass Spectrometry (TM-DART-MS)-based method.

Assessment of a Single Quadrupole Mass Spectrometer Combined with an Atmospheric Solids Analysis Probe for the On-Site Identification of Amnesty Bin Drugs

The surging number of people who abuse drugs has a great impact on healthcare and law enforcement systems. Amnesty bin drug analysis helps monitor the "street drug market" and tailor the harm reduction advice. Therefore, rapid and accurate drug analysis methods are crucial for on-site work. An analytical method for the rapid identification of five commonly detected drugs ((3,4-methylenedioxymethamphetamine (MDMA), cocaine, ketamine, 4-bromo-2,5-dimethoxyphenethylamine, and chloromethcathinone)) at various summer festivals in the U.K. was developed and validated employing a single quadrupole mass spectrometer combined with an atmospheric pressure solids analysis probe (ASAP-MS). The results were confirmed on a benchtop gas chromatography-mass spectrometry instrument and included all samples that challenged the conventional spectroscopic techniques routinely employed on-site. Although the selectivity/specificity step of the validation assessment of the MS system proved a challenge, it still produced 93% (N = 279) and 92.5% (N = 87) correct results when tested on- and off-site, respectively. A few "partly correct" results showed some discrepancies between the results, with the MS-only unit missing some low intensity active ingredients (N-ethylpentylone, MDMA) and cutting agents (caffeine, paracetamol, and benzocaine) or detecting some when not present. The incorrect results were mainly based on library coverage. The study proved that the ASAP-MS instrument can successfully complement the spectroscopic techniques used for qualitative drug analysis on- and off-site. Although the validation testing highlighted some areas for improvement concerning selectivity/specificity for structurally similar compounds, this method has the potential to be used in trend monitoring and harm reduction.

Recent advances in the application of direct analysis in real time-mass spectrometry (DART-MS) in food analysis

Direct analysis in real time-mass spectrometry (DART-MS) has evolved as an effective analytical technique for the rapid and accurate analysis of food samples. The current advancements of DART-MS in food analysis are described in this paper. We discussed the DART principles, which include devices, ionization mechanisms, and parameter settings. Numerous applications of DART-MS in the fields of food and food products analysis published during 2018-2023 were reviewed, including contamination detection, food authentication and traceability, and specific analyte analysis in the food matrix. Furthermore, the challenges and limitations of DART-MS, such as matrix effect, isobaric component analysis, cost considerations and accessibility, and compound selectivity and identification, were discussed as well.

Rapid screening of riot control agents using DART-TD-HRMS

PURPOSE

Riot Control Agents (RCAs) are chemicals used in law enforcement for non-lethal riot control and use in conflicts between states that violates the Chemical Weapons Convention. OPCW's Scientific Advisory Board has identified sixteen potential RCAs including capsaicinoids, CS, and CR. RCAs may be misused for criminal purposes, so methods for detecting such misuse are needed. This study therefore evaluates the feasibility of a rapid, high throughput screening method of RCAs on surfaces (particularly clothing surfaces) by Direct Analysis in Real Time with a thermal desorption unit coupled to high-resolution mass spectrometry (DART-TD-HRMS).

METHODS

A broadly applicable method for detecting potential RCAs was developed and tested on cotton fabric samples sprayed with self-defence sprays from an in-house reference stock. The feasibility of detecting RCAs by direct analysis of surface wipe samples placed in the DART source was also investigated.

RESULTS

The method detected all sixteen RCAs and contaminated clothing were successfully screened for active agents in a reference collection of self-defence sprays. A pilot study also showed that RCAs can be detected by holding a sample directly in front of the DART source.

CONCLUSION

DART-TD-HRMS enables rapid and simple screening of RCAs on fabric samples enabling a high sample throughput.

Matrix- and surface-assisted laser desorption/ionization-mass spectrometry analysis of fingermark components for forensic studies: current trends and future prospects

The chemical analysis of fingermarks (FMs) has attracted considerable attention in the realm of forensic investigations. Techniques based on direct ionization of a sample by laser irradiation, specifically matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), have provided excellent figures of merit for analyzing high molecular-weight compounds. However, it can be challenging to analyze low molecular-weight compounds using MALDI-MS owing to potential interference produced by the organic matrices in the low molecular-weight region, which can impede the detection of small molecules (m/z < 700 Da). Alternately, surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS) has shown great promise for small molecules analysis owing to the unique properties of the nanostructures used, particularly, minimal chemical background in low m/z region improved the production of ions involved in this method. The advancement of MALDI-MS and SALDI-MS has propelled their application in the analysis of FM components, focused on gaining deep insights into individual traits. This review aims to outline the current role of MALDI-MS and SALDI-MS in the chemical analysis of FMs. It also describes the latest achievements in forensic intelligence derived from fingermark analysis using these powerful methods. The accomplishments include the understanding of certain characteristics and lifestyles of donors. The review offers a comprehensive overview of the challenges and demands in this field. It suggests potential enhancements in this rapidly expanding domain to bridge the gap between research and practical police casework.

Rapid Screening of New Psychoactive Substances Using pDART-QqQ-MS

Drug abuse is a severe social problem worldwide. Particularly, the issue of new psychoactive substances (NPSs) have increasingly emerged. NPSs are structural or functional analogs of traditional illicit drugs, such as cocaine, cannabis, and amphetamine; these molecules provide the same or more severe neurological effects. Usually, immunoassays are utilized in the preliminary screening method. However, NPSs have poor detectability in commercially available immunoassay kits. Meanwhile, various chromatography combined with the mass spectrometry platform have been developed to quantify NPSs. Still, a significant amount of time and resources are required during these procedures. Therefore, we established a rapid analytical platform for NPSs employing paper-loaded direct analysis in real time triple quadrupole mass spectrometry (pDART-QqQ-MS). We implemented this platform for the semiquantitative analysis of forensic drug tests in urine. This platform significantly shrinks the analytical time of a single sample within 30 s and requires a low volume of the specimen. The platform can detect 21 NPSs in urine mixtures at a lower limit of qualification of concentration ranging from 20 to 75 nanograms per milliliter (ng mL-1) and is lower than the cutoff value of currently available immune-based devices for detecting multiple drugs (1000 ng mL-1). Urine samples from drug addicts have been collected to verify the platform's effectiveness. By combining efficiency and accuracy, our platform offers a promising solution for addressing the challenges posed by NPSs in drug abuse detection.

Forensic aspects of condom evidence: Analysis, interpretation, and recent trends

In recent years, collection and analysis of condom evidence in sexual assault investigations are becoming more common in forensic caseworks. Condom analysis can provide investigative leads or establish potential contact between the suspect and victim in the absence of DNA evidence or supplement biological evidence. Recent forensic literature shows significant advancements in the analysis of condom lubricants, including casework samples. There is an increasing trend in the use of chemometric tools for the comparison and interpretation of the results. This review highlights the advances in common analytical techniques used for the analysis of condom lubricants with a particular focus on the developments occurring in recent years, including chemometric interpretation. The analysis of reference and casework samples (swab samples, samples on skin, clothing and fingermark) are discussed separately. For casework samples, the transfer and persistence of different lubricant formulations are discussed, along with their detection with various analytical approaches. The issues with the interpretation of lubricants are also discussed in another section, with particular emphasis on samples such as personal hygiene products which have similar formulations with sexual lubricants and the interpretation of negative profiles. The current challenges in the field and prospects for future research are also discussed.

Rapid determination of glyphosate and glufosinate in human blood by probe electrospray ionization tandem mass spectrometry

In forensic science, glyphosate (GLYP) and glufosinate (GLUF), a class of non-selective broad-spectrum herbicides, have been frequently encountered in many fatal poisoning and suicide cases due to their widespread availability. Therefore, it is essential to develop an effective method for detecting these compounds. Some conventional methods, such as gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS), have been reported to detect these compounds. However, these methods are not ideal for their time-consuming and non-sensitive feature. Herein, probe electrospray ionization (PESI) tandem mass spectrometry (MS/MS), a fast and sensitive technique, was applied for the determination of GLYP and GLUF in human blood, which can obtain analytical results within 0.5 min without derivatization and chromatographic separation. After protein precipitation of blood samples, the supernatant was mixed with isopropanol and ultra-pure water (1:1 v/v). Then, 8 μL of the mixture was introduced into the plastic sample plate for PESI-MS/MS analysis. The limits of detection (LODs) of the method were 0.50 μg/mL and 0.25 μg/mL for two analytes, and the limits of quantitation (LOQs) were both 1.00 μg/mL, which are higher than the concentration of reported poisoning and fatal cases. In the linear range of 1-500 μg/mL, the regression coefficients (r2) for GLYP and GLUF were over 0.99. The matrix effects ranged from 94.8 % to 119.5 %, and the biases were below 4.3 %. The recoveries ranged between 84.8 % and 107.4 %, and the biases were below 7.6 %. Meanwhile, the method was effectively utilized to detect and quantify the blood, urine, and other samples. Consequently, the results suggest that PESI-MS/MS is a straightforward, fast, and sensitive method for detecting GLUF and GLYP in forensics. In the future, PESI-MS/MS will become an indispensable technique for polar substances in grassroots units of public security where rapid detection is essential.

Synthetic dyes: A mass spectrometry approach and applications

Synthetic dyes are found in a wide variety of applications today, including but not limited to textiles, foods, and medicine. The analysis of these molecules is pertinent to several fields such as forensics, environmental monitoring, and quality control, all of which require the sensitivity and selectivity of analysis provided by mass spectrometry (MS). Recently, there has been an increase in the implementation of MS evaluation of synthetic dyes by various methods, with the majority of research thus far falling under electrospray ionization and moving toward direct ionization methods. This review covers an overview of the chemistry of synthetic dyes needed for the understanding of MS sample preparation and spectral results, current fields of application, ionization methods, and fragmentation trends and works that have been reported in recent years.

Analytical techniques for screening of cannabis and derivatives from human hair specimens

Cannabis and associated substances are some of the most frequently abused drugs across the globe, mainly due to their anxiolytic and euphorigenic properties. Nowadays, the analysis of hair samples has been given high importance in forensic and analytical sciences and in clinical studies because they are associated with a low risk of infection, do not require complicated storage conditions, and offer a broad window of non-invasive detection. Analysis of hair samples is very easy compared to the analysis of blood, urine, and saliva samples. This review places particular emphasis on methodologies of analyzing hair samples containing cannabis, with a special focus on the preparation of samples for analysis, which involves screening and extraction techniques, followed by confirmatory assays. Through this manuscript, we have presented an overview of the available literature on the screening of cannabis using mass spectroscopy techniques. We have presented a detailed overview of the advantages and disadvantages of this technique, to establish it as a suitable method for the analysis of cannabis from hair samples.

Volatile fingerprints of beef cooking methods using sol-gel-based solid-phase microextraction (SPME) and direct analysis in real-time mass spectrometry (DART-MS)

RATIONALE

The aroma profile of food is a complex mixture of volatile compounds that constitutes a major component of the overall eating experience. The food service industry and chefs therefore constantly seek ways to investigate and thereby enhance the aroma profile. Oven cooking, sous vide and pan fry are three cooking methods of beef commonly practised by chefs. Near real-time analysis of volatile compounds from these three cooking methods will provide insight into respective volatile fingerprints and help improve cooking techniques.

METHODS

Volatile compounds from three beef cooking methods were captured using an in-house sol-gel based solid phase microextraction (SPME) method and analysed using direct analysis in real-time mass spectrometry (DART-MS). A volatile organic compound (VOC) standard was used to demonstrate successful implementation of the sol-gel coating technique. Volatile features discriminating the three cooking methods were shortlisted and statistically assessed by univariate and multivariate analyses.

RESULTS

The VOC standard was successfully adsorbed by the sol-gel method and detected by DART-MS. Hierarchical cluster analysis clearly demarcated three beef cooking methods based on their volatile fingerprints. Out of 65 significant features differentiating the cooking methods, 50 were at highest concentrations from pan-fry cooking only, followed by 14 with highest concentrations from oven cooking followed by pan frying. Sous vide followed by pan frying showed lowest concentrations of almost all volatile features.

CONCLUSIONS

The sol-gel-based solid-phase microextraction technique combined with DART-MS was successful in differentiating beef cooking methods based on their volatile fingerprints. A workflow for rapid assessment of the volatile profile from beef cooking methods was established, providing a baseline to further explore volatile profiles from other key ingredients.

Comparison of direct analysis in real-time mass spectrometry, atmospheric solids analysis probe-mass spectrometry, and ion mobility spectrometry for ensuring food safety by rapid screening of poppy seeds

The opium poppy (Papaver somniferum) is a global commercial crop that has been historically valued for both medicinal and culinary purposes. Naturally occurring opium alkaloids including morphine, codeine, thebaine, noscapine, and papaverine are found primarily in the latex produced by the plant. If the plant is allowed to fully mature, poppy seeds that do not contain the opium alkaloids will form within the pods and may be used in the food industry. It is possible for the seeds to become contaminated with alkaloids by the latex during harvesting, posing a potential health risk for consumers. In the USA, there have been more than 600 reported adverse events including 19 fatalities that may be linked to the consumption of a contaminated poppy-containing product such as home-brewed poppy seed tea. Unwashed poppy seeds and pods may be purchased over the Internet and shipped worldwide. The Forensic Chemistry Center, US Food and Drug Administration (FDA) has evaluated several mass spectrometers (MS) capable of rapid screening to be used for high-throughput analysis of samples such as poppy seeds. These include a direct analysis in real-time (DART) ambient ionization source coupled to a single-quadrupole MS, an atmospheric solids analysis probe (ASAP) ionization source coupled to the same MS, and ion mobility spectrometers (IMS). These instruments have been used to analyze 17 poppy seed samples for the presence of alkaloids, and the results were compared to data obtained using liquid chromatography with mass spectral detection (LC-MS/MS). Results from the 17 poppy seed samples indicate that the DART-MS, ASAP-MS, and IMS devices detect many of the same alkaloids confirmed during the LC-MS/MS analyses, although both the false-positive and false-negative rates are higher, possibly due to the non-homogeneity of the samples and the lack of chromatographic separation.

LMJSSP for analysis of prophylactic lubricants, spermicides and residues

DNA evidence in sexual assault cases have proven increasingly difficult to obtain and analyse due to increased condom use. With more interest in alternatives to DNA evidence, prophylactic lubricants, spermicides and residues may be interesting prospects. Current interest in the analysis of prophylactic residues focuses on the evaluation and identification of lubricants and constituents, primarily through gas chromatography or Fourier transform infrared spectroscopy. Though cost-effective methods, extensive sample preparation and destructive modes of analysis remain an area for improvement. As a result, the focus has since shifted to ambient ionization methods that offer adequate sensitivity and reduced sample preparation. The Liquid Microjunction Surface Sampling Probe (LMJSSP) is a versatile ambient ionization source that employs a probe that supports a continuously flushing droplet that extracts analytes when placed in contact with a surface. The analytes are aspirated into the mass spectrometer with a Venturi pressure. In this work we use the LMJSSP to analyse the trace transfer of condom lubricant to different types of fabric (cotton, cotton-spandex, and denim). Furthermore, we examine the sensitivity and storage conditions for the direct analysis method on different swab types (cotton, silicone, and foam). Additionally, Principal Component Analysis (PCA) and Maximally Collapsing Metric Learning (MCML) are utilized for visualization of differentiability of commercially available condom brands including Durex™ and Trojan™, and product subtypes. The results present an interesting multi-disciplinary approach of using a direct liquid extraction ambient ionization technique and machine learning to improve the overall workflow for the analysis of lubricants, swabs and fabrics. Machine learning algorithms were able to differentiate between inherent differences of Durex™ and Trojan™ condoms.

Rapid headspace solid-phase microextraction sheets with direct analysis in real time mass spectrometry (SPMESH-DART-MS) of derivatized volatile phenols in grape juices and wines

Volatile phenols possess "smoky, spicy" aromas and are routinely measured in grapes, wines and other foodstuffs for quality control. Routine analyses of volatile phenols rely on gas chromatography - mass spectrometry (GC-MS), but slow throughput of GC-MS can cause challenges during times of surge demand, i.e. following 'smoke taint' events involving forest fires near vineyards. Parallel extraction of headspace volatiles onto sorbent sheets (HS-SPMESH) followed by direct analysis in real time mass spectrometry (DART-MS) is a rapid alternative to conventional GC-MS approaches. However, HS-SPMESH extraction is poorly suited for lower volatility odorants, including volatile phenols. This work reports development and validation of an HS-SPMESH-DART-MS approach for five volatile phenols (4-ethylphenol, 4-ethylguiacol, guaiacol, 4-methylguaiacol, and cresols). Prior to HS-SPMESH extraction, volatile phenols were acetylated to facilitate their extraction. A unique feature of this work was the use of d₆-Ac₂O as a derivatizing agent to overcome issues with isobaric interferences inherent to chromatography-free MS techniques. The use of alkaline conditions during derivatization resulted in cumulative measurement of both free and bound forms of volatile phenols. The validated HS-SPMESH-DART-MS method achieved a throughput of 24 samples in ∼60 min (including derivatization and extraction time) with low limits of detection (<1 μg L^-1) and good repeatability (3-6% RSD) in grape and wine matrices. Validation experiments with smoke-tainted grape samples indicated good correlation between total (free + bound) volatile phenols measured by HS-SPMESH-DART-MS and a gold standard GC-MS method.

A feasibility study of direct analysis in real time-mass spectrometry for screening organic gunshot residues from various substrates

This study reports the use of direct analysis in real time-mass spectrometry (DART-MS) for the detection of organic gunshot residues (OGSR) in a variety of matrices of interest for forensics, customs, and homeland security. Detection limits ranged from (0.075 to 12) ng, with intra- and inter-day reproducibility below 0.0012% CV. The collection of mass spectra at multiple in-source collision-induced dissociation (is-CID) voltages produced distinctive mass spectral signatures with varying levels of fragmentation and allowed differentiation of isomers. To test method performance, a collection of 330 authentic specimens from various substrates were analyzed - (1) neat smokeless powders, (2) spent cartridge cases, (3) burnt particles removed from clothing via carbon stubs or (4) with tweezers, and hand samples from (5) non-shooters, and (6) shooters. A subset of hand specimens (n = 80) was further analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) for confirmation and comparison. Seven types of ammunition from five manufacturers and two calibers were monitored for OGSR profiles with similar compositions observed for paired sets (e.g., unburnt smokeless powder and the respective residues on spent cartridges, clothing, and hands). No false positives were observed across all datasets. A 100% true positive rate (TPR) was observed for all substrates except the shooters' hands. Depending on the ammunition type and classification criteria, the shooters' hands exhibited a TPR ranging from 19% to 73%. The results show that DART-MS is feasible and versatile for fast screening of OGSR across various substrates but may benefit from alternative approaches to improve detection at trace levels.

On the challenge of unambiguous identification of fentanyl analogs: Exploring measurement diversity using standard reference mass spectral libraries

Fentanyl analogs are a class of designer drugs that are particularly challenging to unambiguously identify due to the mass spectral and retention time similarities of unique compounds. In this paper, we use agglomerative hierarchical clustering to explore the measurement diversity of fentanyl analogs and better understand the challenge of unambiguous identifications using analytical techniques traditionally available to drug chemists. We consider four measurements in particular: gas chromatography retention indices, electron ionization mass spectra, electrospray ionization tandem mass spectra, and direct analysis in real time mass spectra. Our analysis demonstrates how simultaneously considering data from multiple measurement techniques increases the observable measurement diversity of fentanyl analogs, which can reduce identification ambiguity. This paper further supports the use of multiple analytical techniques to identify fentanyl analogs (among other substances), as is recommended by the Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG).

Rapid Chemical Screening of Microplastics and Nanoplastics by Thermal Desorption and Pyrolysis Mass Spectrometry with Unsupervised Fuzzy Clustering

The transport and chemical identification of microplastics and nanoplastics (MNPs) are critical to the concerns over plastic accumulation in the environment. Chemically and physically transient MNP species present unique challenges for isolation and analysis due to many factors such as their size, color, surface properties, morphology, and potential for chemical change. These factors contribute to the eventual environmental and toxicological impact of MNPs. As analytical methods and instrumentation continue to be developed for this application, analytical test materials will play an important role. Here, a direct mass spectrometry screening method was developed to rapidly characterize manufactured and weathered MNPs, complementing lengthy pyrolysis-gas chromatography-mass spectrometry analysis. The chromatography-free measurements took advantage of Kendrick mass defect analysis, in-source collision-induced dissociation, and advancements in machine learning approaches for the data analysis of complex mass spectra. In this study, we applied Gaussian mixture models and fuzzy c-means clustering for the unsupervised analysis of MNP sample spectra, incorporating clustering stability and information criterion measurements to determine latent dimensionality. These models provided insight into the composition of mixed and weathered MNP samples. The multiparametric data acquisition and machine learning approach presented improved confidence in polymer identification and differentiation.

Direct analysis in real-time mass spectrometry: Observations of helium, nitrogen and argon as ionisation gas for the detection of small molecules using a single quadrupole instrument

RATIONALE

Direct analysis in real time is typically performed using helium as the ionisation gas for the detection of analytes by mass spectrometry (MS). Nitrogen and argon are found with abundance in the air and provide a cheaper and greener alternative to the use of helium as ionisation gas. This study explores the use of helium, nitrogen and argon as ionisation gas for the detection of organic compounds.

METHODS

Four illicit drugs, two amino acids and five explosives were chosen as target analytes to understand selectivity, sensitivity and linearity when helium, nitrogen or argon was used as the ionisation gas with the direct analysis in real time (DART) source. Analysis was carried out on a Waters Acquity QDa single quadrupole mass spectrometer.

RESULTS

Calibration curves over the range of 5-100 ng were produced for each analyte using the different ionisation gases to assess the instrument response. Nitrogen gave a higher response to concentration than helium or argon; however, the lowest limits of detection were observed when helium was used.

CONCLUSIONS

All the target analytes were detected using DART-MS with helium, nitrogen or argon as the ionisation gas. Whereas helium provided the highest sensitivity, nitrogen produced reasonable limits of detection and had good linearity across the concentration range explored, suggesting it provides a greener and cheaper alternative to helium.

Gamma-hydroxybutyrate (GHB), 1,4-butanediol (1,4BD), and gamma-butyrolactone (GBL) intoxication: A state-of-the-art review

γ-hydroxybutyrate (GHB) is synthesized endogenously from γ-aminobutyric acid (GABA) or exogenously from 1,4-butanediol (butane-1,4-diol; 1,4-BD) or γ-butyrolactone (GBL). GBL, and 1,4-BD are rapidly converted to GHB. The gastric absorption time, volume of distribution, and half-life of GHB are between 5 and 45 min, 0.49 ± 0.9 L/kg, and between 20 and 60 min, respectively. GHB and its analogues have a dose-dependent effect on the activation of GHB receptor, GABA-B, and GABA localized to the central nervous system. After ingestion, most patients present transient neurological disorders (lethal dose: 60 mg/kg). Chronic GHB consumption is associated with disorders of use and a withdrawal syndrome when the consumption is discontinued. GHB, GBL, and 1,4-BD are classified as narcotics but only the use of GHB is controlled internationally. They are used for drug facilitated (sexual) assault, recreational purposes, slamsex, and chemsex. To confirm an exogenous intake or administration of GHB, GBL, or 1-4-BD, the pre-analytical conservation is crucial. The antemortem cutoff doses for detection are 5 and 5-15 mg/L, with detection windows of 6 and 10 h in the blood and urine, respectively Control of GHB is essential to limit the number of users, abuse, associated risks, and death related to their consumption.

Rapid Screening of Vaping Liquids by DART-MS

BACKGROUND

E-cigarette, or vaping, product use-associated lung injury was reported in over 2800 cases from August 2019 to February 2020. Samples of vaping products were submitted for laboratory analysis in conjunction with investigation of the outbreak. A rapid screening method that was selective and sensitive for multiple analytes was required to aid in the investigation.

OBJECTIVE

To develop a multi-analyte method capable of screening vaping liquid samples that consumed small amounts of sample, required minimal sample preparation and analysis time, employed automated data processing, and provided the necessary sensitivity and selectivity.

METHODS

Vaping liquids were dissolved in acetonitrile and sampled with DIP-it® tips. The tips were analyzed by direct analysis in real-time mass spectrometry (DART-MS) and the resulting data processed with TraceFinder™ software. Laboratory-fortified samples consisting of various analytes and matrixes were evaluated prior to the analysis of submitted samples.

RESULTS

The method was successful at detecting all target analytes in all matrixes evaluated, although the method detection limits varied by analyte/matrix combination: from 0.1% nicotine in poly(propylene glycol) average Mn 1000 (the lowest level evaluated) to 5.0% poly(ethylene glycol) average Mn 400 in cannabis concentrate. Results for the analysis of submitted samples by this method compared favorably to GC-MS and FTIR results.

CONCLUSION

The DART-MS method met the objective of speed, sensitivity, and selectivity (although certain cannabinoid isomers could not be distinguished). The method may be easily adapted or expanded for additional analytes.

HIGHLIGHTS

This is a simple DART-MS method for screening vaping liquids for substances of concern in less than 2 min per sample.

Ambient Ionization Mass Spectrometry: Application and Prospective

Mass spectrometry (MS) is a formidable analytical tool for the analysis of non-polar to polar compounds individually and/or from mixtures, providing information on the molecular weights and chemical structures of the analytes. During the last more than one-decade, ambient ionization mass spectrometry (AIMS) has developed quickly, producing a wide range of platforms and proving scientific improvements in a variety of domains, from biological imaging to quick quality control. These methods have made it possible to detect target analytes in real time without sample preparation in an open environment, and they can be connected to any MS system with an atmospheric pressure interface. They also have the ability to analyze explosives, illicit drugs, disease diagnostics, drugs in biological samples, adulterants in food and agricultural products, reaction progress, and environmental monitoring. The development of novel ambient ionization techniques, such as probe electrospray ionization, paper spray ionization, and fiber spray ionization, employed even at picolitre to femtolitre solution levels to provide femtogram to attogram levels of the target analytes. The special characteristic of this ambient ion source, which has been extensively used, is the noninvasive property of PESI of examination of biological real samples. The results in the current review supports the idea that AIMS has emerged as a pioneer in MS-based approaches and that methods will continue to be developed along with improvements to existing ones in the near future.

Qualitative Analysis of Real Drug Evidence Using DART-MS and the Inverted Library Search Algorithm

Chromatographic-less mass spectrometry techniques like direct analysis in real-time mass spectrometry (DART-MS) are steadily being employed as seized drug screening tools. However, these newer analytical platforms require new computational methods to best make use of the collected data. The inverted library search algorithm (ILSA) is a recently developed method designed specifically for working with mass spectra of mixtures collected with DART-MS and has been implemented as a function in the NIST/NIJ DART-MS data interpretation tool (DIT). This paper demonstrates how DART-MS and the ILSA/DIT can be used to analyze seized drug evidence, while discussing insights gathered during the evaluation of 92 adjudicated case samples. The evaluation verified that the combination of DART-MS and the ILSA/DIT can be used as an informative tool to help analysts screen seized drug evidence but also revealed several factors─such as the influence of incorporating multiple in-source fragmentation spectra and the effect of scoring thresholds─an analyst must consider while employing these methods. Use cases demonstrating the benefit of the nonscoring metrics provided by the ILSA/DIT and demonstrating how the ILSA/DIT can be used to identify novel substances are also presented. A summary of considerations for using the ILSA/DIT for drug screening concludes this paper.

Rapid GC-MS as a Screening Tool for Forensic Fire Debris Analysis

Techniques developed for the screening of forensic samples can be useful for increasing sample throughput and decreasing backlog in forensic laboratories. One such technique, rapid gas chromatography mass spectrometry (GC-MS), allows for fast sample screening (≈1 min) and has gained interest in recent years for forensic applications. This work focuses on the development of a method for ignitable liquid analysis using rapid GC-MS. A sampling protocol and temperature program were developed for the analysis of these volatile samples. Using the optimized method for analysis, the limits of detection for compounds commonly found in ignitable liquids ranged from 0.012 mg/mL to 0.018 mg/mL. Once the method was developed, neat ignitable liquids (i.e., gasoline and diesel fuel) were analyzed, and major components in each liquid were identified. The identification of major compounds in gasoline and diesel fuel in the presence of substrate interferences was then assessed through the analysis of simulated fire debris samples. Three different substrates were spiked with each ignitable liquid, burned, and analyzed. Major compounds in both liquids were identified using the total ion chromatograms, relevant extracted ion profiles, and deconvolution methods.

Algorithms and Databases: Unlocking Non-Targeted Screening of Small Molecules with Ambient Ionization Mass Spectrometry

Almost all sectors of analytical chemistry are finding applications for ambient ionization mass spectrometry (AI–MS) because of its ease of use, speed of analysis, and sensitivity. Although emphasis has been placed on developing new hardware that can help analyze unique samples across various applications, there has not been much innovation in the functionality of software tools and mass spectral libraries to support applications like non-targeted searching. In this article, we discuss new algorithms and libraries that have enabled non-targeted analysis of small molecules using AI–MS, as well as some of the key considerations and outstanding questions in the field.

Updates to the Inverted Library Search Algorithm for Mixture Analysis

Identifying mixture components is a well-known challenge in analytical chemistry. The Inverted Library Search Algorithm is a recently proposed method for identifying mixture components using in-source collision induced dissociation (is-CID) mass spectra of a query mixture and a reference library of pure compound is-CID mass spectra ( J. Am. Soc. Mass Spectrom. 2021, 32 (7), 1725-1734). This article presents several subtle but important advances to the algorithm, including updated compound matching strategies that improve result explainability and spectral filtering to better handle noisy mass spectra as is often observed with real-world samples such as seized drug evidence.

Opportunities in phytochemistry, ecophysiology and wood research via laser ablation direct analysis in real time imaging-mass spectrometry

Analysis of wood transects in a manner that preserves the spatial distribution of the metabolites present is highly desirable to among other things: (1) facilitate ecophysiology studies that reveal the association between chemical make-up and environmental factors or climatic events over time; and (2) investigate the mechanisms of the synthesis and trafficking of small molecules within specialised tissues. While a variety of techniques could be applied to achieve these goals, most remain challenging and impractical. Laser ablation direct analysis in real time imaging-mass spectrometry (LADI-MS) was successfully used to survey the chemical profile of wood, while also preserving the small-molecule spatial distributions. The tree species Entandrophragma candollei Harms, Millettia laurentii DeWild., Pericopsis elata (Harms) Meeuwen, Dalbergia nigra (Vell.) Benth. and Dalbergia normandii Bosser & R.Rabev were analysed. Several compounds were associated with anatomical features. A greater diversity was detected in the vessels and parenchyma compared with the fibres. Analysis of single vessels revealed that the chemical fingerprint used for timber identification is mainly determined by vessel content. Laser ablation direct analysis in real time imaging-mass spectrometry offers unprecedented opportunities to investigate the distribution of metabolites within wood samples, while circumventing the issues associated with previous methods. This technique opens up new vistas for the discovery of small-molecule biomarkers that are linked to environmental events.

Utilization of Machine Learning for the Differentiation of Positional NPS Isomers with Direct Analysis in Real Time Mass Spectrometry

The differentiation of positional isomers is a well established analytical challenge for forensic laboratories. As more novel psychoactive substances (NPSs) are introduced to the illicit drug market, robust yet efficient methods of isomer identification are needed. Although current literature suggests that Direct Analysis in Real Time-Time-of-Flight mass spectrometry (DART-ToF) with in-source collision induced dissociation (is-CID) can be used to differentiate positional isomers, it is currently unclear whether this capability extends to positional isomers whose only structural difference is the precise location of a single substitution on an aromatic ring. The aim of this work was to determine whether chemometric analysis of DART-ToF data could offer forensic laboratories an alternative rapid and robust method of differentiating NPS positional ring isomers. To test the feasibility of this technique, three positional isomer sets (fluoroamphetamine, fluoromethamphetamine, and methylmethcathinone) were analyzed. Using a linear rail for consistent sample introduction, the three isomers of each type were analyzed 96 times over an eight-week timespan. The classification methods investigated included a univariate approach, the Welch t test at each included ion; a multivariate approach, linear discriminant analysis; and a machine learning approach, the Random Forest classifier. For each method, multiple validation techniques were used including restricting the classifier to data that was only generated on one day. Of these classification methods, the Random Forest algorithm was ultimately the most accurate and robust, consistently achieving out-of-bag error rates below 5%. At an inconclusive rate of approximately 5%, a success rate of 100% was obtained for isomer identification when applied to a randomly selected test set. The model was further tested with data acquired as a part of a different batch. The highest classification success rate was 93.9%, and error rates under 5% were consistently achieved.

Application of direct analysis in real-time mass spectrometry (DART-MS) in forensic science: a comprehensive review

Background

As the rate of crime is constantly increasing, the workload on the forensic analyst also piles up. The availability of a limited number of seized samples makes it crucial to directly analyze the sample, thereby preventing wastage in the prior steps of sample preparation. Due to such needs, the forensic community is consistently working on broadening the usage of direct analysis in real-time mass spectrometry (DART-MS). DART-MS is a relatively new technique for rapid mass spectral analysis. Its use for chemical analysis credits its ability to analyze the sample at atmospheric pressure.

Main body

This article gives insight into the ionization mechanisms, data analysis tools, and the use of hyphenated techniques like thermal-desorption-DART-MS, infrared-thermal-desorption-DART-MS, Joule-heating thermal-desorption-DART-MS, etc. This review summarizes the applications of DART-MS in the field of Forensic Science reported from 2005 to 2021. The applications include analysis of drugs, warfare agents, gun-shot residues, ink differentiation, and other forensically relevant samples. The paper also presents the relation between the type of DART-MS technique and the ionization mode used for a particular class of compounds.

Conclusion

The review follows that the high-resolution mass-spectrometers or low-resolution mass-spectrometers systems in the positive or negative mode were highly dependent on the type of analyte under investigation. Drugs, inks, dyes, and paints were mainly analyzed using the positive ionization mode in the HRMS technique. The examinations of fire accelerants predominantly used the positive ionization mode in the LRMS technique. Moreover, the limit of detection values obtained from the qualitative screening of street drugs were of ppb level, indicating high sensitivity of DART-MS. Considering the work done in the past years, there are potential future research needs of this technology, especially in forensic science.

Graphical Abstract