Determination of drugs and drug-like compounds in different samples with direct analysis in real time mass spectrometry

What is the role of current mass spectrometry in pharmaceutical analysis?

The role of mass spectrometry (MS) has become more important in most application domains in recent years. Pharmaceutical analysis is specific due to its stringent regulation procedures, the need for good laboratory/manufacturing practices, and a large number of routine quality control analyses to be carried out. The role of MS is, therefore, very different throughout the whole drug development cycle. While it dominates within the drug discovery and development phase, in routine quality control, the role of MS is minor and indispensable only for selected applications. Moreover, its role is very different in the case of analysis of small molecule pharmaceuticals and biopharmaceuticals. Our review explains the role of current MS in the analysis of both small-molecule chemical drugs and biopharmaceuticals. Important features of MS-based technologies being implemented, method requirements, and related challenges are discussed. The differences in analytical procedures for small molecule pharmaceuticals and biopharmaceuticals are pointed out. While a single method or a small set of methods is usually sufficient for quality control in the case of small molecule pharmaceuticals and MS is often not indispensable, a large panel of methods including extensive use of MS must be used for quality control of biopharmaceuticals. Finally, expected development and future trends are outlined.

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.

Automatic MDSPE Combined with DART-HRMS for the Rapid Quantitation of 21 Synthetic Cathinones in Urine

A new, rapid, and automated method for the quantitation of 21 synthetic cathinones in urine was established using magnetic dispersive solid-phase extraction (MDSPE) in combination with direct analysis in real time-high-resolution mass spectrometry (DART-HRMS). Sample preparation and quantitation were verified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Methcathinone-D3, α-PVP-D8, and proadifen (SKF525A) were used as internal standards. Magnetic HLB extractant and NaH2PO4/NaOH buffer (0.2 M, pH 7) were used in automatic MDSPE. All 21 synthetic cathinones could be detected and analyzed by DART-HRMS in under 1 min. It was proven that the linearities of 21 synthetic cathinones were suitable (R2 > 0.99) in the concentration ranges of 0.5-100 ng/mL or 1-100 ng/mL. The precision and accuracy values were all within ±15%, and the samples were stable under various conditions. The average time of each sample from preprocessing to completion of detection was approximately 2 min, allowing for rapid sample analysis. The relative error (RE) of the concentrations obtained by DART-HRMS and LC-MS/MS were within ±13.61%, and the linear coefficient (R) was 0.9964. The results of DART-HRMS and LC-MS/MS provided equivalent values at the 95% confidence level. In summary, a simple, fast, and convenient quantitation method via DART-HRMS was established. This application can be utilized to reduce backlogs and promote rapid case processing.

Differentiation of Four Polyvinylidene Fluoride Polymers Based on Their End Groups by DART-FT-ICR MS and Kendrick Plots

Nowadays, synthetic polymers are produced and used in many materials for different applications. Matrix-assisted laser desorption/ionization or electrospray mass spectrometry are classically used to investigate them, but these techniques require sample preparation steps, which are not always suitable for the study of insoluble or formulated polymers. Alternatively, direct real-time (DART) ionization analysis may be conducted without sample preparation. Four polyvinylidene fluoride (PVDF) polymers involving the C2H2F2 repeating unit coming from different suppliers have been analyzed by DART Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in negative-ion mode. The obtained mass spectra systematically displayed an oligomeric distribution between m/z 400 and 1300 of [M - H]-, [M + O2]•-, and [M + NO2]- ions. Kendrick plots were used to ease the identification of PVDF end-groups and establish a difference between the samples. Both commercial PVDF polymers shared the same α+ω end groups formula, which confirmed a similar polymerization process for their synthesis. The two other PVDFs were clearly different from the commercial ones by the occurrence of specific end-groups. MS/MS and MS3 experiments were conducted to obtain structural information on these end-groups.

Ambient ionization mass spectrometry applied to new psychoactive substance analysis

In the past decade a plethora of drugs with similar effects to controlled psychoactive drugs, like cannabis, amfetamine (amphetamine), or lysergic acid diethylamide, have been synthesized. These drugs can collectively be classified under the term new psychoactive substances (NPS) and are used for recreational purposes. The novelty of the substances, alongside the rapid rate of emergence and structural variability, makes their detection as well as their legal control highly challenging, increasing the demand for rapid and easy-to-use analytical techniques for their detection and identification. Therefore, interest in ambient ionization mass spectrometry applied to NPS has grown in recent years, which is largely because it is relatively fast and simple to use and has a low operating cost. This review aims to provide a critique of the suitability of current ambient ionization techniques for the analysis of NPS in the forensic and clinical toxicology fields. Consideration is given to analytical performance and ease of implementation, including ionization efficiency, selectivity, sensitivity, quantification, analyte chemistry, molecular coverage, validation, and practicality.

In situ lipid profiling of insect pheromone glands by direct analysis in real time mass spectrometry

Analysis of biological tissues by Direct Analysis in Real Time mass spectrometry produces semi-quantitative lipid profiles that can be used to distinguish insect species and identify abnormal phenotypes in genetic screens.

FIELDABLE MASS SPECTROMETRY FOR FORENSIC SCIENCE, HOMELAND SECURITY, AND DEFENSE APPLICATIONS

Mass spectrometry is commonly used in forensic chemistry laboratories for sensitive, definitive analysis. There have been significant efforts to bring mass spectrometry analysis on-site through the development of ruggedized, fieldable instruments. Testing samples in the field is of particular interest in forensic science, homeland security, and defense applications. In forensic chemistry, testing seized drugs in the field can significantly improve efficiencies in processing of related criminal cases. The screening of passengers and luggage at transportation hubs is a critical need for homeland security for which mass spectrometry is well suited to provide definitive answers with low false positive rates. Mass spectrometry can yield reliable data for military personnel testing sites for potential chemical weapons release. To meet the needs of the forensic and security communities fieldable mass spectrometers based on membrane inlet systems and hybrid gas chromatography systems have been developed and commercialized. More recently developed ambient ionization mass spectrometry methods can eliminate the time, equipment, and expertise associated with sample preparation, and so are especially appealing for on-site analysis. We describe the development of fieldable mass spectrometry systems, with emphasis on commercially available systems that have been deployed for on-site analysis of seized drugs, chemical warfare agents, explosives, and other analytes of interest to the forensic and security communities. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Saccharose cluster ions as mass calibrants in positive-ion direct analysis in real time-mass spectrometry

In positive-ion direct analysis in real time-mass spectrometry (DART-MS), mono-, di, and trisaccharides form [M+NH₄]⁺ ions. Some of them, in addition, yield abundant [M_n+NH₄]⁺ cluster ions (n = 1-6)), and thus, can serve for mass calibration. Saccharose, C₁₂H₂₂O₁₁, the most common sugar, also termed sucrose, is among the [M_n+NH₄]⁺ cluster ion forming species. Saccharose may therefore be employed as a cheap and ubiquitous mass calibration standard. The extent of saccharose cluster ion formation depends on the temperature of the DART gas, sample load, and instrumental parameters like trapping conditions of ions prior to mass analysis. This study identifies optimized experimental conditions and demonstrates the application of saccharose cluster ion-based mass calibration for accurate mass measurements in DART mode on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer.

Direct analysis in real time-mass spectrometry for rapid quantification of five anti-arrhythmic drugs in human serum: application to therapeutic drug monitoring

Therapeutic drug monitoring (TDM) is necessary for the optimal administration of anti-arrhythmic drugs in the treatment of heart arrhythmia. The present study aimed to develop and validate a direct analysis in real time tandem mass spectrometry (DART–MS/MS) method for the rapid and simultaneous determination of five anti-arrhythmic drugs (metoprolol, diltiazem, amiodarone, propafenone, and verapamil) and one metabolite (5-hydroxy(OH)-propafenone) in human serum. After the addition of isotope-labeled internal standards and protein precipitation with acetonitrile, anti-arrhythmic drugs were ionized by DART in positive mode followed by multiple reaction monitoring (MRM) detection. The use of DART–MS/MS avoided the need for chromatographic separation and allowed rapid and ultrahigh throughput analysis of anti-arrhythmic drugs in a total run time of 30 s per sample. The DART–MS/MS method yielded satisfactory linearity (R² ≥ 0.9906), accuracy (86.1–109.9%), and precision (≤ 14.3%) with minimal effect of biological matrixes. The method was successfully applied to analyzing 30 clinical TDM samples. The relative error (RE) of the concentrations obtained by DART–MS/MS and liquid chromatography-tandem mass spectrometry (LC–MS/MS) was within ± 13%. This work highlights the potential usefulness of DART for the rapid quantitative analysis of anti-arrhythmic drugs in human serum and gives rapid feedback in the clinical TDM practices.

Thermal desorption and pyrolysis direct analysis in real time mass spectrometry for qualitative characterization of polymers and polymer additives

RATIONALE

Direct analysis in real time mass spectrometry (DART-MS) provides qualitative information about additives and polymer composition. However, the observed mass spectra are dependent on sampling conditions, in particular the DART gas temperature. This report describes the combination of a heated sample stage with DART-MS for polymer characterization.

METHODS

Industrial polymers with different compositions were examined by thermal desorption and pyrolysis (TDPy) DART. Samples were heated on disposable copper stages from ambient temperature to 600°C, and the evolved gases were introduced directly into a DART ion source through a glass tee. Time- and temperature-dependent mass spectra were acquired using a high-resolution time-of-flight mass spectrometer. Kendrick mass analysis was applied to the interpretation of complex mass spectra observed for fluorinated polymers.

RESULTS

Positive-ion DART mass spectra of common polymers exhibited peak series differing by monomer masses, often accompanied by a peak corresponding to the protonated monomer. Even polymers that did not exhibit a clear series of peaks produced characteristic mass spectra. Positive-ion and negative-ion mass spectra were recorded for fluorinated polymers, with polytetrafluoroethylene (PTFE) producing only negative ions. Thermal desorption provided characteristic temperature profiles for volatile species such as polymer additives and polymer pyrolysis products.

CONCLUSIONS

In comparison with direct analysis by positioning sample directly in the heated DART gas stream, TDPy DART provides a more versatile sampling method and provides thermal separation and profiling of polymer additives, intact short polymer chains, and pyrolysis fragments.

Atmospheric Solids Analysis Probe Coupled to a Portable Mass Spectrometer for Rapid Identification of Bulk Drug Seizures

The emergence of ambient ionization techniques and their combination with smaller, cheaper mass spectrometers is beginning to make real the possibility of mass spectrometry measurements being made routinely outside of traditional laboratory settings. Here, we describe the development of an atmospheric solids analysis probe (ASAP) source for a commercially available miniaturized, single-quadrupole mass spectrometer and subsequent modification of the instrument to allow it to run as a deployable system; we further go on to describe the application of this instrument to the identification of the contents of drug seizures. For the drug seizure analysis, a small quantity of the material (powder, tablet, resin, etc.) was dissolved in ethanol and shaken to extract the analytes, the resulting solutions were then sampled by dipping a sealed glass capillary into the solution prior to analysis by ASAP-MS. Identification of the contents of the seizures was carried out using a NIST searching approach utilizing a bespoke spectral library containing 46 compounds representative of those most commonly encountered in UK forensic laboratories. In order to increase confidence in identification the library sample and subsequent analyses were carried out using a four-channel acquisition method; each channel in this method used a different cone voltage (15, 30, 50, and 70 V) inducing differing levels of in-source fragmentation in each channel; the match score across each channel was then used for identification. Using this developed method, a set of 50 real-life drug samples was analyzed with each of these being identified correctly using the library searching method.

Nitrogen direct analysis in real time time-of-flight mass spectrometry (N2 DART-TOFMS) for rapid screening of forensic drugs

RATIONALE

Over the last ten years, helium direct analysis in real time time-of-flight mass spectrometry (He DART-TOFMS) has become an established technique in rapid screening of forensic drugs to decrease the time necessary to triage forensic drug cases, therefore contributing to backlog reduction and more timely criminal prosecution. Recently, we demonstrated that N₂ DART was able to efficiently ionize all polar compounds except for a few extremely small ones such as methanol and acetonitrile. Therefore, N₂ DART-TOFMS should be a suitable technique for rapid screening of forensic drugs.

METHODS

Nitrogen direct analysis in real time time-of-flight mass spectrometry (N₂ DART-TOFMS) was performed using a JEOL AccuTOF mass spectrometer with an IonSense DART-100 ion source. A 3-min analytical protocol was used for the analysis of each sample. Sample introduction was accomplished by moving the closed end of a melting point capillary where approximately 1 μL sample solution was deposited or the exposed inside of a freshly cut tablet across the N₂ gas stream between the DART-100 ion source and orifice 1 of the AccuTOF.

RESULTS

Ten commonly abused drugs, eight synthetic cannabinoids and four controlled prescription drugs (CPDs) were analyzed. The limit of detection (LOD) was determined to be approximately 10 μg/mL or 10 pg in quantities. All drugs at the LOD level were positively identified using their [M + H]⁺ ions with mass errors less than 5 mDa. The identification were further supported by in-source fragment ions and characteristic N₂ DART ions that are not commonly generated by He DART, e.g. [M + H + O]⁺ and [M + H + 2O]⁺ ions.

CONCLUSIONS

It was concluded that the 3-min analytical protocol could be utilized in the analysis of seized drugs in the form of tablets and powders or prepared in solution. In consideration that N₂ is readily available in the air and He is a non-renewable resource, N₂ DART-TOFMS is a greener, cheaper and more convenient alternative to He DART-TOFMS in rapid screening of forensic drugs.

Simultaneous determination of multiple components in cigarettes by mechanochemical extraction and direct analysis in real time mass spectrometry in minutes

A simple, rapid and high throughput analytical approach with combination of mechanochemical extraction (MCE) and direct analysis in real time mass spectrometry (DART-MS) analysis was developed for the simultaneous determination of multiple chemical components in cigarette fillers. Different kinds of substances including nicotine, cigarette alkaloids, carbohydrates, organic acids, humectants and other additives were successfully extracted using MCE and detected by high resolution DART-MS. Six solvents of various polarities were compared during MCE process and significant differences were observed. Different brands of cigarettes as well as standard research cigarette exhibited distinctive chemical features and DART-MS fingerprints. Principle component analysis showed clear differentiation among different cigarettes extracted with the same solvent and different solvent extracts of the same type of cigarette. The putative chemical formulas were proposed based on accurate m/z values with <10 ppm mass errors. The relative contents of nicotine and other identified substances were compared and significant differences were observed among cigarettes of different locations. The whole procedure of MCE combined with DART-MS only takes minutes from raw cigarette fillers to obtaining the semi-quantitative results. The operation is simple and high throughput, providing an efficient method to analyze cigarette composition, and to establish a methodology to acquire the rapid cigarette fingerprints for quality control.

New Advances in Toxicological Forensic Analysis Using Mass Spectrometry Techniques

This article reviews mass spectrometry methods in forensic toxicology for the identification and quantification of drugs of abuse in biological fluids, tissues, and synthetic samples, focusing on the methodologies most commonly used; it also discusses new methodologies in screening and target forensic analyses, as well as the evolution of instrumentation in mass spectrometry.

Recent advances in ambient mass spectrometry of trace explosives

Ambient mass spectrometry has evolved rapidly over the past decade, yielding a plethora of platforms and demonstrating scientific advancements across a range of fields from biological imaging to rapid quality control. These techniques have enabled real-time detection of target analytes in an open environment with no sample preparation and can be coupled to any mass analyzer with an atmospheric pressure interface; capabilities of clear interest to the defense, customs and border control, transportation security, and forensic science communities. This review aims to showcase and critically discuss advances in ambient mass spectrometry for the trace detection of explosives.

Ionization Mechanism of Positive-Ion Nitrogen Direct Analysis in Real Time

Nitrogen can be an inexpensive alternative to helium used by direct analysis in real time (DART), especially in consideration of the looming helium shortage. Therefore, the ionization mechanism of positive-ion N₂ DART has been systematically investigated. Our experiments suggest that a range of metastable nitrogen species with a variety of internal energies existed and all of them were less energetic than metastable helium atoms. However, compounds with ionization energies (IE) equal to or lower than 10.2 eV (all organic compounds except the extremely small ones) can be efficiently ionized. Because N₂ DART was unable to efficiently ionize ambient moisture and common organic solvents such as methanol and acetonitrile, the most important ionization mechanism was direct Penning ionization followed by self-protonation of polar compounds generating [M+H]⁺ ions. On the other hand, N₂ DART was able to efficiently ionize ammonia, which was beneficial in the ionization of hydrogen-bonding compounds with proton affinities (PA) weaker than ammonia generating [M+NH₄]⁺ ions and large PAHs generating [M+H]⁺ ions through proton transfer. N₂ DART was also able to efficiently ionize NO, which led to the ionization of nonpolar compounds such as alkanes and small aromatics generating [M-(2m+1)H]⁺ (m=0,1…) ions. Lastly, metastable nitrogen species was also able to produce oxygen atoms, which resulted in increased oxygen adducts as the polarity of organic compounds decreased. In comparison with He DART, N₂ DART was approximately one order of magnitude less sensitive in generating [M+H]⁺ ions, but could be more sensitive in generating [M+NH₄]⁺ ions. Graphical Abstract ᅟ.

Confirmation of Pharmaceutical Identifiers via DART-TOF-MS

A direct analysis in real time ion source coupled with a time-of-flight mass spectrometer (DART-TOF-MS) is a suitable confirmatory technique for the analysis of pharmaceutical preparations, with accompanying reference sources for preparation markings. The DART-TOF-MS instrument allows for simple sample preparation and decreased analysis time, both crucial in a forensic laboratory setting. Differentiation can be made between active drug ingredients with the same molecular weight, such as hydrocodone and codeine, as well as pharmaceutical preparation mixtures, such as oxycodone and acetaminophen, using exact masses of the protonated molecules and fragment peaks compared to a standard.

Use of DART-TOF-MS for Screening Drugs of Abuse

Screening is an integral component of an analytical scheme to identify the presence of controlled substances in submissions to the crime laboratory. Many techniques are utilized, including color tests, thin-layer chromatography, and ultraviolet spectroscopy. While these are useful techniques to guide the examiner, all will, at best, categorize the material into a broad group of compounds. Direct Analysis in Real Time (DART), coupled with a time-of-flight (TOF) mass spectrometer, is an emerging technique that yields highly definitive screening data leading to the identity of controlled substances present in a case sample. Sample preparation is quick and simple and run times are typically only a few minutes. Collected data will allow the examiner to determine appropriate standards for confirmation, making the overall analysis much more efficient. Presented here is a guide to using this technique for the screening of case submissions for controlled substances.

Ion mobility spectrometry nuisance alarm threshold analysis for illicit narcotics based on environmental background and a ROC-curve approach

The discriminative potential of an ion mobility spectrometer (IMS) for trace detection of illicit narcotics relative to environmental background was investigated with a receiver operating characteristic (ROC) curve framework. The IMS response of cocaine, heroin, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA), and Δ(9)-tetrahydro-cannabinol (THC) was evaluated against environmental background levels derived from the screening of incoming delivery vehicles at a federal facility. Over 20 000 samples were collected over a multiyear period under two distinct sets of instrument operating conditions, a baseline mode and an increased desorption/drift tube temperature and sampling time mode. ROC curves provided a quantifiable representation of the interplay between sensitivity (true positive rate, TPR) and specificity (1 - false positive rate, FPR). A TPR of 90% and minimized FPR were targeted as the detection limits of IMS for the selected narcotics. MDMA, THC, and cocaine demonstrated single nanogram sensitivity at 90% TPR and <10% FPR, with improvements to both MDMA and cocaine in the elevated temperature/increased sampling mode. Detection limits in the tens of nanograms with poor specificity (FPR ≈ 20%) were observed for methamphetamine and heroin under baseline conditions. However, elevating the temperature reduced the background in the methamphetamine window, drastically improving its response (90% TPR and 3.8% FPR at 1 ng). On the contrary, the altered mode conditions increased the level of background for THC and heroin, partially offsetting observed enhancements to desorption. The presented framework demonstrated the significant effect environmental background distributions have on sensitivity and specificity.

Detection of polydimethylsiloxanes transferred from silicone-coated parchment paper to baked goods using direct analysis in real time mass spectrometry

The non-stick properties of parchment papers are achieved by polydimethylsiloxane (PDMS) coatings. During baking, PDMS can thus be extracted from the silicone-coated parchment into the baked goods. Positive-ion direct analysis in real time (DART) mass spectrometry (MS) is highly efficient for the analysis of PDMS. A DART-SVP source was coupled to a quadrupole-time-of-flight mass spectrometer to detect PDMS on the contact surface of baked goods after use of silicone-coated parchment papers. DART spectra from the bottom surface of baked cookies and pizzas exhibited signals because of PDMS ions of the general formula [(C2H6SiO)n  + NH4 ](+) in the m/z 800-1900 range.

Mass spectrometric detection of trace anions: The evolution of paired-ion electrospray ionization (PIESI)

The negative-ion mode of electrospray ionization mass spectrometry (ESI-MS) is intrinsically less sensitive than the positive-ion mode. The detection and quantitation of anions can be performed in positive-ion mode by forming specific ion-pairs during the electrospray process. The paired-ion electrospray ionization (PIESI) method uses specially synthesized multifunctional cations to form positively charged adducts with the anions to be analyzed. The adducts are detected in the positive-ion mode and at higher m/z ratios to produce excellent signal-to-noise ratios and limits of detection that often are orders of magnitude better than those obtained with native anions in the negative-ion mode. This review briefly summarizes the different analytical approaches to detect and separate anions. It focuses on the recently introduced PIESI method to present the most effective dicationic, tricationic, and tetracationic reagents for the detection of singly and multiply charged anions and some zwitterions. The mechanism by which specific structural molecular architectures can have profound effects on signal intensities is also addressed.

Improved desorption/ionization and ion transmission in surface scanning by direct analysis in real time mass spectrometry

RATIONALE

Modifications to the Direct Analysis in Real Time mass spectrometry (DART-MS) interface, its source cap and transfer tube were necessary to obtain highest efficiency in desorption and ionization from the sampling surface and in ion transmission into the MS system. These issues are crucial for the trace analysis of any surface and the hyphenation of high-performance thin-layer chromatography (HPTLC) with DART-MS.

METHODS

The ion source mounting was modified to enable short source caps to be utilized in combination with a short transfer tube. The grid voltage contact section was readjusted to increase the intensity of the metastable gas stream towards the substrate. Eighteen different cap and two transfer tube geometries (including gas-stream focusing), along with the influence of their distance from the mass spectrometer glass capillary, were investigated for best signal intensity.

RESULTS

Using shortened source caps with staged inner bore, a transfer tube with gas-stream focusing and an optimized mounting geometry for DART-MS scanning along five identical deposited bands (600 ng each) of butyl 4-hydroxybenzoate, an average signal precision of 3.6% was obtained and the signal intensity was increased by a factor of 34. The width of the gas impact area did not exceed 1.5 mm and the smallest FWHM was determined to be 0.9 mm.

CONCLUSIONS

The desorption strength, ionization efficacy and ion transmission were improved significantly giving increased detectability using this further modified DART-MS interface with reduced cap length and optimum transfer tube geometry. The resolution was comparable with state-of-the-art densitometry. With this setup, reliable HPTLC surface scanning is possible, even for substance amounts in the low-nanogram range.

Thermal-assisted gasification injector for analyzing high-salt solution samples: a novel device developed for online coupling of liquid chromatography with direct analysis in real time mass spectrometry

A thermal-assisted gasification injector was designed for online coupling of liquid-chromatography to direct-analysis-in-real-time mass-spectrometry. The method can be used in analysis with an inorganic salt matrix and weak polar solvent.

Letter: High-mass capabilities of positive-ion and negative-ion direct analysis in real time mass spectrometry

Of the ionic liquid 1-butyl-3-methylimidazolium (C(+)) tricyanomethide (A(-)) high-mass cluster ions of both positive ([C(n)A(n-1)](+)) and negative ([C(n-1)A(n)](-)) charge were generated and detected by direct analysis in real time (DART) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS). After optimization of the settings of the DART ionization source and of the mass analyzer ions of m/z values unprecedented in DART-MS were detected. Thus, the upper m/z limits of positive-ion and negative-ion DART- MS were substantially expanded. Negative-ion DART-MS delivered cluster ions up to [C(15)A(16)](-), m/z 3527 (nominal mass of monoisotopic ion), while positive-ion DART-MS even yielded ions up to [C(30)A(29)](+), m/z 6784. The identification of the cluster ions is supported by their accurate mass and exact mass differences corresponding to CA between adjacent cluster ion peaks.

Plasma-based ambient mass spectrometry techniques: The current status and future prospective

Plasma-based ambient mass spectrometry is emerging as a frontier technology for direct analysis of sample that employs low-energy plasma as the ionization reagent. The versatile sources of ambient mass spectrometry (MS) can be classified according to the plasma formation approaches; namely, corona discharge, glow discharge, dielectric barrier discharge, and microwave-induced discharge. These techniques allow pretreatment-free detection of samples, ranging from biological materials (e.g., flies, bacteria, plants, tissues, peptides, metabolites, and lipids) to pharmaceuticals, food-stuffs, polymers, chemical warfare reagents, and daily-use chemicals. In most cases, plasma-based ambient MS performs well as a qualitative tool and as an analyzer for semi-quantitation. Herein, we provide an overview of the key concepts, mechanisms, and applications of plasma-based ambient MS techniques, and discuss the challenges and outlook.

Quantitative surface scanning by Direct Analysis in Real Time mass spectrometry

RATIONALE

Only a few ambient ionization sources have been demonstrated to work quantitatively for surface scanning. A modification of the Direct Analysis in Real Time mass spectrometry (DART-MS) interface is needed to improve the precision during the scanning of a high-performance thin-layer chromatography (HPTLC) plate or any other surface or planar substrate, especially for quantitation without an internal standard correction.

METHODS

The substrate movement relative to the ion source outlet and the mass spectrometer inlet was optimized to improve the desorption, ionization, and capture of analytes. The substrate carrier was mounted at an angled position, thus reducing collisions between the deflected gas stream and the inner transfer tube wall. A special transfer tube, whose edge was angled towards the substrate and allowed a narrow set-up of the ambient air gap, captured the deflected DART gas stream.

RESULTS

For the repeated DART-MS scanning along five identical deposited bands of butyl-4-hydroxybenzoate a mean precision of 2.7% was obtained. A signal decay of 62% was observed after five scans. After HPTLC of methyl-4-hydroxybenzoate and butyl-4-hydroxybenzoate, mean determination coefficients of 0.9937 and 0.9906 were obtained for five calibrations on five plates, respectively. The mean recovery of two control standards was 94% with a mean repeatability of 9% (%RSD, n = 5) obtained on five different plates.

CONCLUSIONS

The DART SVPA-3DS system remained compact and the access to the substrate was kept wide open despite the optimized scan lane (spatial resolution at full width at half maximum 0.8 mm, height 3 mm). The performance data showed that the quantitative surface scanning was improved as well as the desorption efficacy and detectability using this modified DART-MS interface.

Analysis of silicones released from household items and baby articles by direct analysis in real time-mass spectrometry

Direct analysis in real time-mass spectrometry (DART-MS) enables screening of articles of daily use made of polydimethylsiloxanes (PDMS), commonly known as silicone rubber, to assess their tendency to release low molecular weight silicone oligomers. DART-MS analyses were performed on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Flexible silicone baking molds, a watch band, and a dough scraper, as baby articles different brands of pacifiers, nipples, and a teething ring have been examined. While somewhat arbitrarily chosen, the set can be regarded as representative of household items, baby articles, and other objects made of silicone rubber. For comparison, two brands of silicone septa and as blanks a glass slide and a latex pacifier were included. Differences between the objects were mainly observed in terms of molecular weight distribution and occasional release of other compounds in addition to PDMS. Other than that, all objects made of silicone rubber released significant amounts of PDMS during DART analysis. To provide a coarse quantification, a calibration based on silicone oil was established, which delivered PDMS losses from 20 μg to >100 μg during the 16-s period per measurement. Also, the extraction of baking molds in rapeseed oil demonstrated a PDMS release at the level of 1 μg mg(-1). These findings indicate a potential health hazard from frequent or long-term use of such items. This work does not intend to blame certain brands of such articles. Nonetheless, a higher level of awareness of this source of daily silicone intake is suggested.

Polydimethylsiloxane extraction from silicone rubber into baked goods detected by direct analysis in real time mass spectrometry

Flexible baking molds and other household utensils are made of polydimethylsiloxane (PDMS), also known as silicone rubber. PDMS is prone to release oligomers upon elongated contact with fats, e.g., in the process of baking dough. Positive-ion direct analysis in real time (DART) mass spectrometry (MS) provides an efficient tool for the analysis of PDMS up to m/z 3000. Here, DART ionization is employed in combination with Fourier transform ion cyclotron resonance MS to detect PDMS released into muffins when baked in silicone rubber baking molds. Intensive signals caused by PDMS do occur in the m/z 700-1500 range of DART mass spectra obtained from the crusty surface of muffins after the use of such silicone rubber molds. In addition, triacylglyceroles (TAGs) present as natural ingredients of the analyzed muffins were detected as [TAG+NH(4)](+) ions.

Authentication of true cinnamon (Cinnamon verum) utilising direct analysis in real time (DART)-QToF-MS

The use of cinnamon as a spice and flavouring agent is widespread throughout the world. Many different species of plants are commonly referred to as 'cinnamon'. 'True cinnamon' refers to the dried inner bark of Cinnamomum verum J. S. Presl (syn. C. zeylanicum) (Lauraceae). Other 'cinnamon' species, C. cassia (Nees & T. Nees) J. Presl (syn. C. aromaticum Nees) (Chinese cassia), C. loureiroi Nees (Saigon cassia), and C. burmannii (Nees & T. Nees) Blume (Indonesian cassia), commonly known as cassia, are also marketed as cinnamon. Since there is a prevalence of these various types of 'cinnamons' on the market, there is a need to develop a rapid technique that can readily differentiate between true cinnamon (C. verum) and other commonly marketed species. In the present study, coumarin and other marker compounds indicative of 'cinnamon' were analysed using DART-QToF-MS in various samples of cinnamon. This method involved the use of [M + H](+) ions in positive mode in addition to principal component analysis (PCA) using Mass Profiler Professional software to visualise several samples for quality and to discriminate 'true cinnamon' from other Cinnamomum species using the accurate mass capabilities of QToF-MS.

Wide-range mass calibration for negative-ion DART mass spectrometry

A method for accurate mass calibration covering a wide m/z range in negative-ion direct analysis in real time mass spectrometry (DART-MS) is described. It is based on a commercially available tuning solution (Agilent ES tune mix) normally applied in electrospray ionization. This acetonitrile solution is composed of ammonium trifluoroacetate, betaine, 2,4,6-tris(heptafluoropropyl)-1,3,5-triazine, and various symmetrical hexakis-(fluoroalkoxy)-phosphazenes. Upon addition of 2% (v/vl trifluoroacetic acid in negative-ion DART-MS, this mixture yields negative ions covering a range of m/z 69 to m/z 2834. Validity of the calibration procedure is demonstrated on a Fourier transform ion cyclotron resonance mass spectrometer by application to polyethylene glycol diacid and [60]fullerene. Experimental conditions and a mass reference list are provided.

Trace analysis of energetic materials via direct analyte-probed nanoextraction coupled to direct analysis in real time mass spectrometry

Direct analysis in real time mass spectrometry (DART-MS) has proven to be a useful forensic tool for the trace analysis of energetic materials. While other techniques for detecting trace amounts of explosives involve extraction, derivatization, solvent exchange, or sample clean-up, DART-MS requires none of these. Typical DART-MS analyses directly from a solid sample or from a swab have been quite successful; however, these methods may not always be an optimal sampling technique in a forensic setting. For example, if the sample were only located in an area which included a latent fingerprint of interest, direct DART-MS analysis or the use of a swab would almost certainly destroy the print. To avoid ruining such potentially invaluable evidence, another method has been developed which will leave the fingerprint virtually untouched. Direct analyte-probed nanoextraction coupled to nanospray ionization-mass spectrometry (DAPNe-NSI-MS) has demonstrated excellent sensitivity and repeatability in forensic analyses of trace amounts of illicit drugs from various types of surfaces. This technique employs a nanomanipulator in conjunction with bright-field microscopy to extract single particles from a surface of interest and has provided a limit of detection of 300 attograms for caffeine. Combining DAPNe with DART-MS provides another level of flexibility in forensic analysis, and has proven to be a sufficient detection method for trinitrotoluene (TNT), RDX, and 1-methylaminoanthraquinone (MAAQ).