Use of proton transfer reaction time-of-flight mass spectrometry for the analytical detection of illicit and controlled prescription drugs at room temperature via direct headspace sampling

Demonstrating the Applicability of Proton Transfer Reaction Mass Spectrometry to Quantify Volatiles Emitted by the Mycoparasitic Fungus Trichoderma atroviride in Real Time: Monitoring of Trichoderma-Based Biopesticides

The present study aims to explore the potential application of proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) for real-time monitoring of microbial volatile organic compounds (MVOCs). This investigation can be broadly divided into two parts. First, a selection of 14 MVOCs was made based on previous research that characterized the MVOC emissions of Trichoderma atroviride, which is a filamentous fungus widely used as a biocontrol agent. The analysis of gas-phase standards using PTR-ToF-MS allowed for the categorization of these 14 MVOCs into two groups: the first group primarily undergoes nondissociative proton transfer, resulting in the formation of protonated parent ions, while the second group mainly undergoes dissociative proton transfer, leading to the formation of fragment ions. In the second part of this investigation, the emission of MVOCs from samples of T. atroviride was continuously monitored over a period of five days using PTR-ToF-MS. This also included the first quantitative online analysis of 6-amyl-α-pyrone (6-PP), a key MVOC emitted by T. atroviride. The 6-PP emissions of T. atroviride cultures were characterized by a gradual increase over the first two days of cultivation, reaching a plateau-like maximum with volume mixing ratios exceeding 600 ppbv on days three and four. This was followed by a marked decrease, where the 6-PP volume mixing ratios plummeted to below 50 ppbv on day five. This observed sudden decrease in 6-PP emissions coincided with the start of sporulation of the T. atroviride cultures as well as increasing intensities of product ions associated with 1-octen-3-ol and 3-octanone, whereas both these MVOCs were previously associated with sporulation in T. atroviride. The study also presents the observations and discussion of further MVOC emissions from the T. atroviride samples and concludes with a critical assessment of the possible applications and limitations of PTR-ToF-MS for the online monitoring of MVOCs from biological samples in real time.

Air monitoring for illegal drugs including new psychoactive substances: A review of trends, techniques and thermal degradation products

The detection of illicit psychotropic substances in both indoor and outdoor air is a challenging analytical discipline, and the data from such investigation may provide intelligence in a variety of fields. Applications of drug monitoring in air include providing data on national and international drug consumption trends, as monitored by organisations such as the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) and the United Nations Office on Drugs and Crime (UNODC). Air monitoring enables mapping of illicit drug manufacturing, dealing or consumption in cities and the identification of emergent compounds including the recent proliferation of new psychoactive substances (NPS). The rapid spread of NPS has changed the global drug market with greater diversity and dynamic spread of such compounds over several nations. This review provides an up to date analysis of key thematic areas within this analytical discipline. The process of how illicit psychotropic substances spread from emission sources to the atmosphere is considered alongside the sampling and analytical procedures involved. Applications of the technique applied globally are reviewed with studies ranging from the analysis of individual dwellings through to major international air-monitoring campaigns providing evidence on global drug trends. Finally, we consider thermal breakdown products of illicit psychotropic substances including NPS that are released upon heating, combustion or vaping and related potential for exposure to these compounds in the air.

Studies pertaining to the monitoring of volatile halogenated anaesthetics in breath by proton transfer reaction mass spectrometry

Post-operative isoflurane has been observed to be present in the end-tidal breath of patients who have undergone major surgery, for several weeks after the surgical procedures. A major new non-controlled, non-randomized, and open-label approved study will recruit patients undergoing various surgeries under different inhalation anaesthetics, with two key objectives, namely (1) to record the washout characteristics following surgery, and (2) to investigate the influence of a patient's health and the duration and type of surgery on elimination. In preparation for this breath study using proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS), it is important to identify first the analytical product ions that need to be monitored and under what operating conditions. In this first paper of this new research programme, we present extensive PTR-TOF-MS studies of three major anaesthetics used worldwide, desflurane (CF₃CHFOCHF₂), sevoflurane ((CF₃)₂CHOCH₂F), and isoflurane (CF₃CHClOCHF₂) and a fourth one, which is used less extensively, enflurane (CHF₂OCF₂CHFCl), but is of interest because it is an isomer of isoflurane. Product ions are identified as a function of reduced electric field (E/N) over the range of approximately 80 Td to 210 Td, and the effects of operating the drift tube under 'normal' or 'humid' conditions on the intensities of the product ions are presented. To aid in the analyses, density functional theory (DFT) calculations of the proton affinities and the gas-phase basicities of the anaesthetics have been determined. Calculated energies for the ion-molecule reaction pathways leading to key product ions, identified as ideal for monitoring the inhalation anaesthetics in breath with a high sensitivity and selectivity, are also presented.

Selective Reagent Ion Mass Spectrometric Investigations of the Nitroanilines

This paper presents an investigation of proton and charge transfer reactions to 2-, 3- and 4-nitroanilines (C₆H₆N₂O₂) involving the reagent ions H₃O⁺·(H₂O)_n (n = 0, 1 and 2) and O₂⁺, respectively, as a function of reduced electric field (60-240 Td), using Selective Reagent Ion-Time-of-Flight-Mass Spectrometry (SRI-ToF-MS). To aid in the interpretation of the H₃O⁺·(H₂O)_n experimental data, the proton affinities and gas-phase basicities for the three nitroaniline isomers have been determined using density functional theory. These calculations show that proton transfer from both the H₃O⁺ and H₃O⁺·H₂O reagent ions to the nitroanilines will be exoergic and hence efficient, with the reactions proceeding at the collisional rate. For proton transfer from H₃O⁺ to the NO₂ sites, the exoergicities are 171 kJ mol^-1 (1.8 eV), 147 kJ mol^-1 (1.5 eV) and 194 kJ mol^-1 (2.0 eV) for 2-, 3- and 4-nitroanilines, respectively. Electron transfer from all three of the nitroanilines is also significantly exothermic by approximately 4 eV. Although a substantial transfer of energy occurs during the ion/molecule reactions, the processes are found to predominantly proceed via non-dissociative pathways over a large reduced electric field range. Only at relatively high reduced electric fields (> 180 Td) is dissociative proton and charge transfer observed. Differences in fragment product ions and their intensities provide a means to distinguish the isomers, with proton transfer distinguishing 2-nitroaniline (2-NA) from 3- and 4-NA, and charge transfer distinguishing 4-NA from 2- and 3-NA, thereby providing a means to enhance selectivity using SRI-ToF-MS.

Proton transfer reaction time-of-flight mass spectrometric measurements of volatile compounds contained in peppermint oil capsules of relevance to real-time pharmacokinetic breath studies

With the growing interest in the use of breath volatiles in the health sciences, the lack of standardization for the sampling and analysis of exhaled breath is becoming a major issue leading to an absence of conformity, reproducibility and reliability in spectrometric measurements. Through the creation of a worldwide 'peppermint consortium', the International Association of Breath Research has set up a task force to deal with this problem. Pharmacokinetic studies are proposed, and a real-time analytical technique that is being used is proton transfer reaction-time-of-flight-mass spectrometry (PTR-ToF-MS). This paper presents details on how the volatile compounds contained in a peppermint oil capsule, and hence on breath, appear in a PTR-ToF-MS. To aid that study, the key volatiles in the headspace of peppermint oil were first identified using gas chromatography-mass spectrometry, notably: menthol, menthone, 1,8-cineole, menthofuran, limonene, α-pinene and β-pinene. A PTR-ToF-MS analysis of these compounds has been undertaken, divorced from the complexity of the peppermint oil matrix using 'normal' and 'saturated' humidity drift-tube conditions, with the latter used to mimic breath samples, and over a range of reduced electric fields. There are no characteristic product ions that can distinguish monoterpenes and 1,8-cineole, and hence, without pre-separation, a combined washout for these volatiles can only be provided. By operating the drift tube above about 130 Td, there are characteristic product ions for menthone, menthofuran and menthol, namely m/z 155.14 (protonated menthone), m/z 151.11 (protonated menthofuran), m/z 139.15 (loss of H₂O from protonated menthol) and m/z 83.09 (a fragment ion, C₆H₁₁ ⁺, from menthol). These have been used to monitor, with a high specificity, the temporal profile of these three compounds in breath following the ingestion of a peppermint oil capsule. To aid in the analyses, the proton affinities and gas-phase basicities for the key volatiles investigated have been determined using density functional theory.

Ammonia-Assisted Proton Transfer Reaction Mass Spectrometry for Detecting Triacetone Triperoxide (TATP) Explosive

Proton transfer reaction mass spectrometry (PTR-MS) usually detects different types of compounds by changing the discharge gas to produce different reagent ions in the ion source. In the present work, a novel method of changing reagent ions, ammonia-assisted PTR-MS, was developed. Through an injection port bypass, ammonia was injected into a homemade PTR-MS device. A conventional PTR-MS apparatus with reagent ions H₃O⁺(H₂O)_n (n = 0, 1, 2) can be converted to an ammonia-assisted PTR-MS with reagent ions NH₄⁺.The new method was introduced to detect triacetone triperoxide (TATP) explosive material. Results showed that the sensitivity is enhanced more than 37 times compared with TATP detection using conventional PTR-MS and the limit of detection (LOD) could reach 1.3 ppb. TATP in real complex matrixes can also be detected successfully using this method. Compared to conventional PTR-MS, ammonia-assisted PTR-MS has better sensitivity and better LOD for TATP detection, and the technique provides common users with a convenient and quick method to change reagent ions. The users of PTR-MS can easily obtain other reagent ions by injecting different assisted gases into an injection port to meet different detection needs. Graphical Abstract.

Limonene in exhaled breath is elevated in hepatic encephalopathy

Breath samples were taken from 31 patients with liver disease and 30 controls in a clinical setting and proton transfer reaction quadrupole mass spectrometry (PTR-Quad-MS) used to measure the concentration of volatile organic compounds (VOCs). All patients had cirrhosis of various etiologies, with some also suffering from hepatocellular cancer (HCC) and/or hepatic encephalopathy (HE). Breath limonene was higher in patients with No-HCC than with HCC, median (lower/upper quartile) 14.2 (7.2/60.1) versus 3.6 (2.0/13.7) and 1.5 (1.1/2.3) nmol mol^-1 in controls. This may reflect disease severity, as those with No-HCC had significantly higher UKELD (United Kingdom model for End stage Liver Disease) scores. Patients with HE were categorized as having HE symptoms presently, having a history but no current symptoms and having neither history nor current symptoms. Breath limonene in these groups was median (lower/upper quartile) 46.0 (14.0/103), 4.2 (2.6/6.4) and 7.2 (2.0/19.1) nmol mol^-1, respectively. The higher concentration of limonene in those with current symptoms of HE than with a history but no current symptoms cannot be explained by disease severity as their UKELD scores were not significantly different. Longitudinal data from two patients admitted to hospital with HE show a large intra-subject variation in breath limonene, median (range) 18 (10-44) and 42 (32-58) nmol mol^-1.

Volatile Biomarkers in Breath Associated With Liver Cirrhosis - Comparisons of Pre- and Post-liver Transplant Breath Samples

Background

The burden of liver disease in the UK has risen dramatically and there is a need for improved diagnostics.

Aims

To determine which breath volatiles are associated with the cirrhotic liver and hence diagnostically useful.

Methods

A two-stage biomarker discovery procedure was used. Alveolar breath samples of 31 patients with cirrhosis and 30 healthy controls were mass spectrometrically analysed and compared (stage 1). 12 of these patients had their breath analysed after liver transplant (stage 2). Five patients were followed longitudinally as in-patients in the post-transplant period.

Results

Seven volatiles were elevated in the breath of patients versus controls. Of these, five showed statistically significant decrease post-transplant: limonene, methanol, 2-pentanone, 2-butanone and carbon disulfide. On an individual basis limonene has the best diagnostic capability (the area under a receiver operating characteristic curve (AUROC) is 0.91), but this is improved by combining methanol, 2-pentanone and limonene (AUROC curve 0.95). Following transplant, limonene shows wash-out characteristics.

Conclusions

Limonene, methanol and 2-pentanone are breath markers for a cirrhotic liver. This study raises the potential to investigate these volatiles as markers for early-stage liver disease. By monitoring the wash-out of limonene following transplant, graft liver function can be non-invasively assessed.

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Breath volatiles were compared for cirrhotic patients and controls and pre- and post-liver transplant.

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Three volatiles (limonene, methanol, 2-pentanone) have been found to have excellent diagnostic capabilities.

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Limonene shows washout characteristics following transplant supporting a hypothesis that it accumulates in fat.

There are numerous previous studies investigating breath volatiles in patients with liver disease but with conflicting results. It is impossible to tell which volatiles from previous studies may be false discoveries, and which are actually associated with the disease. We measured breath samples in patients and controls and in patients after transplant. Methanol, 2-pentanone and limonene show differences not only between patients and controls but also in cases pre- and post-transplant and have excellent diagnostic capabilities. We show evidence that limonene accumulates in the body, probably because the cirrhotic liver fails to metabolise dietary limonene.

Selective reagent ionisation-time of flight-mass spectrometry: a rapid technology for the novel analysis of blends of new psychoactive substances

In this study we demonstrate the potential of selective reagent ionisation-time of flight-mass spectrometry for the rapid and selective identification of a popular new psychoactive substance blend called 'synthacaine', a mixture that is supposed to imitate the sensory and intoxicating effects of cocaine. Reactions with H3O(+) result in protonated parent molecules which can be tentatively assigned to benzocaine and methiopropamine. However, by comparing the product ion branching ratios obtained at two reduced electric field values (90 and 170 Td) for two reagent ions (H3O(+) and NO(+)) to those of the pure chemicals, we show that identification is possible with a much higher level of confidence then when relying solely on the m/z of protonated parent molecules. A rapid and highly selective analytical identification of the constituents of a recreational drug is particularly crucial to medical personnel for the prompt medical treatment of overdoses, toxic effects or allergic reactions.

Headspace analysis of new psychoactive substances using a Selective Reagent Ionisation-Time of Flight-Mass Spectrometer

The rapid expansion in the number and use of new psychoactive substances presents a significant analytical challenge because highly sensitive instrumentation capable of detecting a broad range of chemical compounds in real-time with a low rate of false positives is required. A Selective Reagent Ionisation-Time of Flight-Mass Spectrometry (SRI-ToF-MS) instrument is capable of meeting all of these requirements. With its high mass resolution (up to m/Δm of 8000), the application of variations in reduced electric field strength (E/N) and use of different reagent ions, the ambiguity of a nominal (monoisotopic) m/z is reduced and hence the identification of chemicals in a complex chemical environment with a high level of confidence is enabled. In this study we report the use of a SRI-ToF-MS instrument to investigate the reactions of H₃O⁺, O₂⁺, NO⁺ and Kr⁺ with 10 readily available (at the time of purchase) new psychoactive substances, namely 4-fluoroamphetamine, methiopropamine, ethcathinone, 4-methylethcathinone, N-ethylbuphedrone, ethylphenidate, 5-MeO-DALT, dimethocaine, 5-(2-aminopropyl)benzofuran and nitracaine. In particular, the dependence of product ion branching ratios on the reduced electric field strength for all reagent ions was investigated and is reported here. The results reported represent a significant amount of new data which will be of use for the development of drug detection techniques suitable for real world scenarios.

Distinguishing two isomeric mephedrone substitutes with selective reagent ionisation mass spectrometry (SRI-MS)

The isomers 4-methylethcathinone and N-ethylbuphedrone are substitutes for the recently banned drug mephedrone. We find that with conventional proton transfer reaction mass spectrometry (PTR-MS), it is not possible to distinguish between these two isomers, because essentially for both substances, only the protonated molecules are observed at a mass-to-charge ratio of 192 (C12 H18NO(+)). However, when utilising an advanced PTR-MS instrument that allows us to switch the reagent ions (selective reagent ionisation) from H3O(+) (which is commonly used in PTR-MS) to NO(+), O2(+) and Kr(+), characteristic product (fragment) ions are detected: C4H10N(+) (72 Da) for 4-methylethcathinone and C5 H12N(+) (86 Da) for N-ethylbuphedrone; thus, selective reagent ionisation MS proves to be a powerful tool for fast detection and identification of these compounds.

Investigations of chemical warfare agents and toxic industrial compounds with proton-transfer-reaction mass spectrometry for a real-time threat monitoring scenario

RATIONALE

Security and protection against terrorist attacks are major issues in modern society. One especially challenging task is the monitoring and protection of air conditioning and heating systems of buildings against terrorist attacks with toxic chemicals. As existing technologies have low selectivity, long response times or insufficient sensitivity, there is a need for a novel approach such as we present here.

METHODS

We have analyzed various chemical warfare agents (CWAs) and/or toxic industrial compounds (TICs) and related compounds, namely phosgene, diphosgene, chloroacetone, chloroacetophenone, diisopropylaminoethanol, and triethyl phosphate, utilizing a high-resolution proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOFMS) instrument with the objective of finding key product ions and their intensities, which will allow a low-resolution quadrupole mass spectrometry based PTR-MS system to be used with high confidence in the assignment of threat agents in the atmosphere.

RESULTS

We obtained high accuracy PTR-TOFMS mass spectra of the six compounds under study at two different values for the reduced electric field in the drift tube (E/N). From these data we have compiled a table containing product ions, and isotopic and E/N ratios for highly selective threat compound detection with a compact and cost-effective quadrupole-based PTR-MS instrument. Furthermore, using chloroacetophenone (tear gas), we demonstrated that this instrument's response is highly linear in the concentration range of typical Acute Exposure Guideline Levels (AEGLs).

CONCLUSIONS

On the basis of the presented results it is possible to develop a compact and cost-effective PTR-QMS instrument that monitors air supply systems and triggers an alarm as soon as the presence of a threat agent is detected. We hope that this real-time surveillance device will help to seriously improve safety and security in environments vulnerable to terrorist attacks with toxic chemicals.

Rapid and facile detection of four date rape drugs in different beverages utilizing proton transfer reaction mass spectrometry (PTR-MS)

In this work, we illustrate the application of proton transfer reaction mass spectrometry (PTR-MS) in the field of food and drink safety. We present proof-of-principle measurements of four different drinks (water, tea, red wine and white wine) each spiked separately with four different date rape drugs (chloral hydrate, tricholorethanol, γ-butyrolactone and butanediol). At first, the ideal PTR-MS operating conditions (reduced electric field strength and monitoring the most abundant [fragment] ion) for detection of the drugs were determined utilizing a time-of-flight-based PTR-MS instrument. We then dissolved small quantities of the drugs (below the activation threshold for effects on humans) into the various types of drinks and detected them using a quadrupole-based PTR-MS instrument via two different sampling methods: (1) dynamic headspace sampling and (2) direct liquid injection. Both methods have their advantages and drawbacks. Only with dynamic headspace sampling can rape drug contaminations be detected within a timeframe of seconds, and therefore, this method is the most promising use of PTR-MS as a fast, sensitive and selective monitor for the detection of food and drink contamination.

Detection of isocyanates and polychlorinated biphenyls using proton transfer reaction mass spectrometry

RATIONALE

Isocyanates are highly reactive species widely used in industry. They can cause irritation of the eyes, trigger asthma, etc. Polychlorinated biphenyls (PCBs) were widely used in electrical equipments like capacitors and transformers in the last century and are still present in the environment today. PCBs are known to cause cancer and to affect the immune, reproductive, nervous and endocrine systems. Therefore, there is a need for a simple, rapid and reliable analytical method for the detection of traces of isocyanates and of PCBs.

METHODS

The data presented in this paper were obtained using a proton transfer reaction (PTR) time-of-flight mass spectrometer and a high sensitivity PTR quadrupole mass spectrometer. We also utilized a recently developed direct aqueous injection (DAI) inlet system for proton transfer reaction mass spectrometry (PTR-MS) instruments that allows the analysis of trace compounds in liquids.

RESULTS

We detected four isocyanates in the headspace above small sample quantities and investigated their fragmentation pathways to obtain a fundamental understanding of the processes involved in proton transfer reactions and also to determine the best operating conditions of the PTR-MS instruments. In addition, nine PCBs were unambiguously identified via their exact mass and isotopic distribution and detected in different concentration levels via direct injection of the liquid.

CONCLUSIONS

Utilizing recent developments and improvements in PTR-MS, we can rapidly detect two important environmental pollutant compound classes (isocyanates and PCBs) at high accuracy and without any sample preparation. In this paper, we provide proof of the detection of traces of isocyanates and PCBs in air and also of PCBs in liquids. These results could be used for the development of a real-time monitoring device for industrial waste, polluted air or water quality surveillance.