Enhanced Compound Analysis Using Reactive Paper Spray Mass Spectrometry: Leveraging Schiff Base Reaction for Amino Acid Detection.

Paper spray mass spectrometry (PS-MS) has evolved into a promising tool for monitoring reactions in thin films and microdroplets, known as reactive PS, alongside its established role in ambient and direct ionization. This study addresses the need for rapid, cost-effective methods to improve analyte identification in biofluids by leveraging reactive PS-MS in clinical chemistry environments. The technique has proven effective in derivatizing target analytes, altering hydrophobicity to enhance elution and ionization efficiency, and refining detection through thin-film reactions on paper, significantly expediting reaction rates by using amino acids (AAs) as model analytes. These molecules are prone to interacting with substrates like paper, impeding elution and detection. Additionally, highly abundant species in biofluids, such as lipids, often suppress AA ionization. This study employs the Schiff base (SB) reaction utilizing aromatic aldehydes for AA derivatization to optimize reaction conditions time, temperature, and catalyst presence and dramatically increasing the conversion ratio (CR) of formed SB. For instance, using leucine as a model AA, the CR surged from 57% at room temperature to 89% at 70 °C, with added pyridine during and after 7.5 min, displaying a 43% CR compared to the bulk reaction. Evaluation of various aromatic aldehydes as derivatization agents highlighted the importance of specific oxygen substituents for achieving higher conversion rates. Furthermore, diverse derivatization agents unveiled unique fragmentation pathways, aiding in-depth annotation of the target analyte. Successfully applied to quantify AAs in human and rat plasma, this reactive PS-MS approach showcases promising potential in efficiently detecting conventionally challenging compounds in PS-MS analysis.

Low-cost heat assisted ambient ionization source for mass spectrometry in food and pharmaceutical screening.

Ambient Ionization Mass Spectrometry (AI-MS) techniques have revolutionized analytical chemistry by enabling rapid analysis of samples under atmospheric conditions with minimal to no preparation. In this study, the optimization of a cold atmospheric plasma for the analysis of food and pharmaceutical samples, liquid and solid, using a Heat-Assisted Dielectric Barrier Discharge Ionization (HA-DBDI) source is described. A significant enhancement in analyte signals was observed when a heating element was introduced into the design, potentially allowing for greater sensitivity. Furthermore, the synergy between the inlet temperature of the mass spectrometer and the heating element allows for precise control over the analytical process, leading to improved detection sensitivity and selectivity. Incorporating computational fluid dynamic (CFD) simulations into the study elucidated how heating modifications can influence gas transport properties, thereby facilitating enhanced analyte detection and increased signal intensity. These findings advance the understanding of HA-DBDI technology and provide valuable insights for optimizing AI-MS methodologies for a wide range of applications in food and pharmaceutical analysis.

Soft ionization mechanisms in flexible µ-tube plasma-from FµTP to closed µ-tube plasma.

In order to find an explanation for the mechanism in a plasma operated with an alternating voltage, or rather a square wave voltage, such a plasma was investigated. It was found that Penning ionization, charge transfer, and photoionization played a minor or even no role in the soft ionization mechanism of a FµTP. If the collision of plasma gases with air does not contribute to soft ionization, it should also be possible to use a separated plasma for soft ionization. Preliminary investigations show that it is possible to ignite a diagnosis gas with a plasma gas even when there is a barrier such as glass between those gases. A temporally and locally limited potential must be produced at the outer surface to achieve this. This potential should be sufficient to ionize the environment softly and to be able to use this so-called closed µ-tube plasma as a new ionization source.

Soft ionization mechanisms in flexible µ-tube plasma-elucidation of He-, Ar-, Kr-, and Xe-FµTP.

The soft ionization mechanism of helium-based plasma seems to be understood while it still remains challenging in argon-based plasma, although many studies have used argon plasmas as a soft ionization source with good ionization efficiencies. In this study, helium, argon, krypton, and xenon were fed into the same discharge geometry, a flexible micro-tube plasma (FµTP), to determine the ionization mechanisms. The FµTPs operated with the named noble gases obtained comparable ionization efficiencies by MS measurements. The optical emission results showed that N2+ were the dominant ions within the helium-FµTP and noble gas ions were dominant for the other plasmas. These ions support the development of excitation and eventually stop at the end of the capillary. Therefore, Penning ionization and charge transfer between plasma and ambient air/analytes in the open atmosphere have been proven not to be the primary soft ionization mechanism. Furthermore, it was found that photoionization played a minor role in soft ionization. Using helium as a diagnosis gas in front of the discharge capillary nozzle of the FµTP, where the sample is usually positioned, shows that helium can be ignited by all of these FµTPs. This demonstrates that the excitation of a diagnosis gas as well as the ionization of analytes is independent of the type of the discharge gas. An alternative mechanism that a transient potential created by the ions is responsible for the soft ionization is subsequently proposed.

Solvent-Assisted Laser Desorption Flexible Microtube Plasma Mass Spectrometry for Direct Analysis of Dried Samples on Paper.

The present study investigated the potential for solvent-assisted laser desorption coupled with flexible microtube plasma ionization mass spectrometry (SALD-FµTP-MS) as a rapid analytical technique for direct analysis of surface-deposited samples. Paper was used as the demonstrative substrate, and an infrared hand-held laser was employed for sample desorption, aiming to explore cost-effective sampling and analysis methods. SALD-FµTP-MS offers several advantages, particularly for biofluid analysis, including affordability, the ability to analyze low sample volumes (<10 µL), expanded chemical coverage, sample and substrate stability, and in situ analysis and high throughput potential. The optimization process involved exploring the use of viscous solvents with high boiling points as liquid matrices. This approach aimed to enhance desorption and ionization efficiencies. Ethylene glycol (EG) was identified as a suitable solvent, which not only improved sensitivity but also ensured substrate stability during analysis. Furthermore, the addition of cosolvents such as acetonitrile/water (1:1) and ethyl acetate further enhanced sensitivity and reproducibility for a standard solution containing amphetamine, imazalil, and cholesterol. Optimized conditions for reproducible and sensitive analysis were determined as 1000 ms of laser exposure time using a 1 µL solvent mixture of 60% EG and 40% acetonitrile (ACN)/water (1:1). A mixture of 60% EG and 40% ACN/water (1:1) resulted in signal enhancements and relative standard deviations of 12, 20, and 13% for the evaluated standards, respectively. The applicability of SALD-FµTP-MS was further evaluated by successfully analyzing food, water, and biological samples, highlighting the potential of SALD-FµTP-MS analysis, particularly for thermolabile and polarity diverse compounds.

Flexible Microtube Plasma for the Consecutive-Ionization of Cholesterol in Nano-Electrospray Mass Spectrometry.

Electrospray ionization mass spectrometry (ESI-MS) is an established method for the identification of biomarkers. By nano-ESI (nESI), the polar molecular fraction of complex biological samples can be successfully ionized. In contrast, the less-polar free cholesterol, which serves as an important biomarker for several human diseases, is barely accessible by nESI. Although, complex scan functions of modern high-resolution MS devices are able to increase the signal-to-noise ratio, they are limited by the ionization efficiency of the nESI. One possible method to increase the ionization efficiency is the derivatization with acetyl chloride, however interferences with cholesteryl esters must be considered, so chromatographic separation or complex scan functions may be required. A novel approach to increase the yield of cholesterol ions of the nESI could be the application of a second consecutive-ionization process. This publication presents the flexible microtube plasma (FµTP) as a consecutive-ionization source, which allows the determination of cholesterol in nESI-MS analysis. Focusing on the analytical performance, the nESI-FµTP approach increases the cholesterol signal yield in a complex liver extract by a factor of 49. The repeatability and long-term stability could be successfully evaluated. A linear dynamic range of 1.7 orders of magnitude, a minimum detectability of 5.46 mg/L, and a high accuracy (deviation, -8.1%) demonstrates the nESI-FµTP-MS as an excellent approach for a derivatization-free determination of cholesterol.

Dielectric Barrier Discharge Ionization Mechanisms: Polycyclic Aromatic Hydrocarbons as a Case of Study.

Dielectric barrier discharge ionization (DBDI) is a versatile tool for small-molecule mass spectrometry applications, helping cover from polar to low polar molecules. However, the plasma gas-phase interactions are highly complex and have been scarcely investigated. The ionization mechanisms of plasmas have long been assumed to be somewhat similar to atmospheric pressure chemical ionization (APCI). Here, we evaluated the ionization mechanisms of a two-ring DBDI ion source, using different discharge gases to analyze vaporized liquid samples. Polycyclic aromatic hydrocarbons (PAHs) were used as model analytes to assess the mechanisms' dominance: protonation, [M + H]+, or radical ion species formation, [M]·+. In the present work, two different ionization trends were observed for APCI and DBDI during the PAH analysis; the compounds with proton affinities (PA) over 856 kJ/mol were detected as [M + H]+ when APCI was used as ionization source. Meanwhile, independently of the PA, DBDI showed the prevalence of charge exchange reactions. The addition of dopants in the gas-phase region shifted the ionization mechanisms toward charge exchange reactions, facilitating the formation of [M]·+ ion species, showing anisole a significant boost of the PAH radical ion species signals, over nine times for Ar-Prop-DBDI analysis. The presence of high-energy metastable atoms (e.g., HeM) with high ionization potentials (IE = 19.80 eV) did not show boosted PAH abundances or extensive molecule fragmentation. Moreover, other species in the plasma jet region with closer and more appropriate IE, such as N2 B3Πg excited molecules, are likely responsible for PAH Penning ionization.

Liquid chromatography-dielectric barrier discharge ionization mass spectrometry for the analysis of neutral lipids of archaeological interest.

Dielectric barrier discharge ionization has gained attention in the last few years due to its versatility and the vast array of molecules that can be ionized. In this study, we report on the assessment of liquid chromatography coupled to dielectric barrier discharge ionization with mass spectrometry for neutral lipid analysis. A set of different neutral lipid subclasses (triacylglycerides, diacylglycerides, and sterols) were selected for the study. The main species detected from our ionization source were [M-H2 O+H]+ , [M+H]+ or [M-R-H2 O+H]+ , attributed to sterol dehydration, protonation or the fragmentation of an acyl chain accompanied by a water loss of the glycerolipids, respectively. In terms of sensitivity, the dielectric barrier discharge displayed overall improved abundances and comparable or better limits of quantitation than atmospheric pressure chemical ionization for both acylglycerols and sterols. As a case study, different archaeological samples with variable content in neutral lipids, particularly triacylglycerides, were studied. The identification was carried out by combining accurate mass and the tentative formula associated with the exact mass, retention time matching with standards, and additional structural information from in-source fragmentation. The high degree of unsaturation and the presence of sterols revealed the potential vegetal origin of the material stored in the analyzed samples.

Detection and Evaluation of Lipid Classes and Other Hydrophobic Compounds Using a Laser Desorption/Plasma Ionization Interface.

Ionization mechanisms of different lipid classes and other hydrophobic compounds have been evaluated in an ambient air laser-desorption flexible microtube plasma ionization (LD-FµTPi) setup, without sample manipulation. Lipids require a minimum laser fluency of 27 W/mm2 for efficient desorption and detection, providing the possibility for temperature-programmed laser desorption of different lipid classes. The flexible microtube plasma (FµTP) produces oxygen addition to double bonds, even to polyunsaturated molecules. The characteristic fragmentation pattern of phospholipids consisting of the neutral loss of the phosphocholine head group was verified. The formation of dimers due to hydrogen bonding and dispersion forces was observed as well. In this sense, soft ionization capabilities of the FµTP were proven in both ion modes. Ambient air mass spectrometry methods often suffer from decreased reproducibility, for instance, due to changing atmospheric conditions or sensitive positioning of the ion source. It was shown that neutrals become increasingly unstable above a distance of 7 ± 1 mm to the spectrometer's inlet, providing estimates for the free volume in LD-FµTPi MS. In this sense, no guided transport is required. The ion plume ejected from the plasma can be altered by applying a bias voltage to the copper substrate. Ions can be detected at -950 V, 300 V (negative ion mode) and -400 V, 900 V (positive ion mode), respectively. The ions are guided through an internal electric field gradient of the FµTP that arises from charged capillary walls, ideal for ion detection. In conclusion, this makes the method fast, robust, and flexible.

Standardization of Sandwich-Structured Cu-Glass Substrates Embedded in a Flexible Diode Laser-Plasma Interface for the Detection of Cholesterol.

This study introduced sandwich-structured copper-glass substrates for standardization of laser desorption and plasma ionization. For standardized quantitative analysis, cavities were constructed which allow better reproducibility in droplet deposition and for laser application. Applying the diode laser, molten substrate material is incorporated into the glass, being trapped inside. Therefore, this method can be separated from laser ablation, achieving high ion signals without ablating material from the surface. Flexible microtube plasma (FµTP) was selected as the ionization source, this being the first time that laser desorption and FµTP ionization are coupled. This laser-plasma interface was applied to the detection of cholesterol, which showed a significantly improved limit of detection of 0.46 ng and linear dynamic range of 3 orders of magnitude in positive ion mode compared to other (ambient air mass spectrometry) methods. The main reason was the change of phase on the copper surface. The dehydrated molecule [M-H2O+H]+ was the base peak of the spectrum and no further dissociation or fragmentation was observed. Blood plasma was spiked with cholesterol. In a 1:100 chloroform dilution, the presence of the plasma was neglectable and led to the same detection limits and linear dynamic range as in the cholesterol standard. No sample preparation or internal standards were needed for calibration. The physical effects of the surface modification were investigated, including the calculation of the laser beam waist to simplify the comparison and reproducibility of results.

Study of Controlled Atmosphere Flexible Microtube Plasma Soft Ionization Mass Spectrometry for Detection of Volatile Organic Compounds as Potential Biomarkers in Saliva for Cancer.

A new soft ionization device for mass spectrometry is presented using the flexible microtube plasma under controlled atmospheric conditions. The controlled atmosphere flexible microtube plasma consists of the plasma source itself connected to a gas chromatograph and a mass spectrometer using a borosilicate glass cross piece. Controlled atmosphere, for example, nitrogen and/or an oxygen mixture, is introduced to the system to create a clean ionization environment. Reproducibility issues are discussed, and solutions are presented manipulating the gas flow in the cross piece. A proof of concept is shown using a ketone mixture introduced to the mass spectrometer to optimize atmospheric conditions. Furthermore, application of the presented device for the sensitive and nonfragmenting ionization of volatile organic biomarkers relevant for cancer is carried out. Sample treatment for human saliva is described, and relevant candidate biomarkers are measured in the saliva matrix, showing a very good ionization efficiency and neglectable matrix effects with limits of detection below 80 ppt.

Analyte-Tailored Controlled Atmosphere Improves Dielectric Barrier Discharge Ionization Mass Spectrometry Performance.

Plasma sources in atmospheric pressure soft-ionization mass spectrometry have gained significant interest in recent years. As many of these sources are used under ambient air conditions, their interaction with the surrounding atmosphere plays an important role in the ionization pathway. This study focuses on the interaction between the plasma source and the surrounding atmosphere by connecting the plasma source to the mass spectrometer using a 2 mm ID closed reactant capillary supplied by a reactant gas up to 500 mL per minute to gain a controlled atmosphere. Different reactant gases (Ar, He, O2, and N2) and reactant gas mixtures are tested with regard to the DBDI performance and then used to improve the ionization efficiency. Tailoring the controlled atmosphere for a certain analyte, for example, perfluorinated compounds, leads to significantly improved limits of detection up to 2 ppb.

Characterization of a Nitrogen-Based Dielectric Barrier Discharge Ionization Source for Mass Spectrometry Reveals Factors Important for Soft Ionization.

Atmospheric pressure plasma-based ionization coupled to mass spectrometry is a powerful analytical technique. However, the characteristics of existing ionization sources, especially regarding the reactive species and the effect of the discharge type on the soft ionization, are often not well described. In this work, the active capillary plasma ionization source, which is based on a dielectric barrier discharge, was characterized by optical emission spectroscopy and mass spectrometry. To obtain a better understanding of the requirements for a soft ionization, several reactive species and the energy of the ionization reaction were identified. Charged reactive species such as H3O+, N2+•, N2H+, NO+, N3+, and N4+• as well as uncharged species (most probably the excited neutral nitrogen) were all found to contribute to the soft ionization process in dielectric barrier discharge. The energy in the plasma was determined to be in the range from 8 to 16 eV, based on the ionization energy of nitrogen and the measurements of tungsten hexacarbonyl. Furthermore, not only was the type of reactive species relevant for achieving a soft ionization, it was also crucial that the sample was injected through the inner electrode, which leads to nearly no direct contact with the discharge filaments.

Detection of multiclass explosives and related compounds in soil and water by liquid chromatography-dielectric barrier discharge ionization-mass spectrometry.

In this work, the multiclass detection of explosives and related compounds has been studied by liquid chromatography-high-resolution mass spectrometry by means of a time-of-flight mass spectrometer (TOFMS) operated in the negative ion mode, using dielectric barrier discharge ionization (DBDI). Reversed-phase high-performance liquid chromatography (HPLC) separation was performed using water-methanol mobile phase without any modifier, although the effect of ammonium acetate was studied. DBD plasma was generated by applying a square wave voltage of 2.5 kV to a 100-mL min-1 He flow. The DBDI probe was adjusted to fit the commercial API source housing so that the HPLC eluent was nebulized and vaporized in the same manner as for atmospheric-pressure chemical ionization (APCI). The ionization process was affected by the temperature of the two nitrogen streams used to vaporize the solvent and the analytes, particularly for RDX and HMX, which are thermolabile compounds. The best approach in terms of sensitivity for all the studied compounds was the use of a gradient of temperatures in the ionization source, starting at 225/200 °C (vaporizer/drying gas temp) for nitramines and ending at 350/325 °C for nitroaromatic compounds. High-resolution full-scan spectra of individual selected compounds were recorded by LC-DBDI-TOFMS, and the results were compared to LC-APCI-TOFMS. A better sensitivity (slope of calibration curve) was obtained by DBDI for more than 70% of the studied compounds in both wastewater and soil extracts. Graphical abstract ᅟ.

Mechanistic Understanding Leads to Increased Ionization Efficiency and Selectivity in Dielectric Barrier Discharge Ionization Mass Spectrometry: A Case Study with Perfluorinated Compounds.

Perfluorinated compounds have unique properties and many practical applications, but are difficult to ionize efficiently with soft ionization methods. An active capillary plasma ionization source based on dielectric barrier discharge ionization (DBDI) coupled with mass spectrometry was used to study the ionization pathway of perfluorinated compounds (PFCs), with the aim of both increasing the ionization efficiency and influencing the selectivity for generating product ions in negative ion mode. Cyclic and linear perfluorinated alkanes were found to mainly form [M - F]- and [M - F + O]- ions, respectively; the [M]-• ion was only obtained at low discharge voltage. Additionally, fluorine attachment [M + F]- was observed mostly for perfluorinated alkenes. An isotope labeling experiment with 18O2 showed that the primary source of oxygen in the substitution reaction is molecular oxygen, reacting with the analyte in the form of O-• ions. The abundance of [M - F + O]- ions can thus be enhanced by increasing the plasma voltage to produce a higher O-• ion density. The loss of the fluorine (without substitution by oxygen) was mainly observed at high frequency, a fact which can be exploited for tuning the ionization toward specific product ions. Overall, the mechanistic understanding of the ionization of PFCs allowed to increase the selectivity of the product ions, resulting in increased ionization efficiency.

Spatially and Temporally Resolved Detection of Arsenic in a Capillary Dielectric Barrier Discharge by Hydride Generation High-Resolved Optical Emission Spectrometry.

A new method for arsenic detection by optical emission spectrometry (OES) is presented. Arsine (AsH3) is generated from liquid solutions by means of hydride generation (HG) and introduced into a capillary dielectric barrier discharge (DBD) where it is atomized and excited. A great challenge in OES is the reduction of the recorded background signal, because it negatively affects the limit of detection (LOD). In conventional DBD/OES methods, the signal intensity of the line of interest, in this case arsenic, is integrated over a long time scale. However, due to the pulsed character of the plasma, the plasma on-time is only a small fraction of the integration time. Therefore, a high amount of noise is added to the actual signal in each discharge cycle. To circumvent this, in the present study the emitted light from the DBD is collected by a fast gated iCCD camera, which is mounted on a modified monochromator. The experimental arrangement enables the recording of the emission signal of arsenic in the form of a monochromatic 2D-resolved picture. The temporal resolution of the iCCD camera in the nanosecond range provides the information at which point in time and how long arsenic is excited in the discharge. With use of this knowledge, it is possible to integrate only the arsenic emission by temporally isolating the signal from the background. With the presented method, the LOD for arsenic could be determined to 93 pg mL-1 with a calibration curve linear over 4 orders of magnitude. As a consequence, the developed experimental approach has a potential for both mechanistic studies of arsine atomization and excitation in DBD plasmas as well as routine applications, in which arsenic determination at ultratrace levels is required.

Flexible Microtube Plasma (FµTP) as an Embedded Ionization Source for a Microchip Mass Spectrometer Interface.

Dielectric barrier discharges are used as soft ionization sources for mass spectrometers or ion mobility spectrometers, enabling excellent possibilities for analytical applications. A new robust and small-footprint discharge design, flexible microtube plasma (FµTP), developed as a result of ongoing miniaturization and electrode design processes, is presented in this work. This design provides major safety benefits by fitting the electrode into an inert flexible fused silica capillary (tube). Notably, in this context, the small discharge dimensions enable very low gas flows in the range of <100 mL min-1; portability; the use of hydrogen, nitrogen, and air in addition to noble gases such as helium and argon, including its mixtures with propane; and application in microchip environments. By coupling FµTP with gas chromatography/mass spectrometry, we show that the polarity principle of the new discharge design allows it to outperform established ionization sources such as dielectric barrier discharge for soft ionization (DBDI) and low-temperature plasma (LTP) at low concentrations of perfluoroalkanes in terms of sensitivity, ionization efficiency, chemical background, linear dynamic range, and limit of detection by a large margin. In negative ion mode, the limit of detection is improved by more than 3-fold compared with that of DBDI and by 8-fold compared with that of LTP. The protonation capability was evaluated by headspace measurements of diisopropyl methylphosphonate in positive ion mode, showing low fragmentation and high stability in comparison to DBDI and LTP.

Soft Argon-Propane Dielectric Barrier Discharge Ionization.

Dielectric barrier discharges (DBDs) have been used as soft ionization sources (DBDI) for organic mass spectrometry (DBDI-MS) for approximately ten years. Helium-based DBDI is often used because of its good ionization efficiency, low ignition voltage, and homogeneous plasma conditions. Argon needs much higher ignition voltages than helium when the same discharge geometry is used. A filamentary plasma, which is not suitable for soft ionization, may be produced instead of a homogeneous plasma. This difference results in N2, present in helium and argon as an impurity, being Penning-ionized by helium but not by metastable argon atoms. In this study, a mixture of argon and propane (C3H8) was used as an ignition aid to decrease the ignition and working voltages, because propane can be Penning-ionized by argon metastables. This approach leads to homogeneous argon-based DBDI. Furthermore, operating DBDI in an open environment assumes that many uncharged analyte molecules do not interact with the reactant ions. To overcome this disadvantage, we present a novel approach, where the analyte is introduced in an enclosed system through the discharge capillary itself. This nonambient DBDI-MS arrangement is presented and characterized and could advance the novel connection of DBDI with analytical separation techniques such as gas chromatography (GC) and high-pressure liquid chromatography (HPLC) in the near future.

Screening of semifluorinated n-alkanes by gas chromatography coupled to dielectric barrier discharge ionization mass spectrometry.

RATIONALE: The potential of an atmospheric pressure ionization source based on a dielectric barrier discharge in helium for the hyphenation of gas chromatography and mass spectrometry (GC/DBDI-MS) has been demonstrated only recently and for a limited range of compounds. Due to its 'soft' ionization properties and the possibility to choose from a variety of atmospheric pressure ionization MS instruments, GC/DBDI-MS has the potential to be an interesting alternative to 'classic' GC/MS techniques. METHODS: The hyphenation of GC with DBDI-MS at atmospheric pressure is used for the determination of semifluorinated n-alkanes in ski wax samples. RESULTS: Different to perfluorinated n-alkanes, which are typically detected as [M - F + O]- and [M - F]- , semifluorinated n-alkanes can be detected both in positive mode as [M - 3H + nO]+ and [M - H + nO]+ (n = 0, 1, 2, and 3) ions, as well as in negative mode as a fragment ion representing the fluorinated part of the respective semifluorinated n-alkane. The method allowed the sensitive detection of semifluorinated n-alkanes with achievable limits of detection (LODs) in the single digit pg range injected on column. To examine the applicability of the GC/DBDI-MS method, semifluorinated n-alkanes were determined in fluorinated ski waxes. Results were confirmed by complimentary GC/electron ionization MS measurements. CONCLUSIONS: The unique SFA ionization patterns serve for complementary unambiguous identification of semifluorinated n-alkane species in positive mode and screening of contained n-alkanes fluorinated chain lengths in negative mode.

Determination of Peroxide Explosive TATP and Related Compounds by Dielectric Barrier Discharge Ionization-Mass Spectrometry (DBDI-MS).

Dielectric barrier discharge ionization-mass spectrometry (DBDI-MS), which is based on the use of a low temperature helium plasma as ionization source, is used for the determination of trace amounts of triacetone triperoxide (TATP) and its homologue diacetone diperoxide (DADP) from surfaces. TATP is observed as [M+NH4]+ adduct, whereas DADP is observed as [M+O+NH4]+. Measurement of DADP with varying deuteration degrees (DADP, DADP-d6, and DADP-d12) indicates that DADP undergoes oxidation when ionized by DBDI. If acetonitrile is used as deposition solvent, TATP tends to show fragmentation and is not only detected as [M+NH4]+ but as [M-CH4+NH4]+ and [M-C2H4+NH4]+ as well. Quantification of TATP solutions from glass surfaces by DBDI-MS, using TATP-3,6,9-13C as internal standard, was done and validated using an LC/APCI-MS method. Achievable limits of detection (LOD) for TATP are equivalent to the deposition of 15 ng TATP and are comparable with other ambient desorption/ionization mass spectrometric techniques like desorption electrospray ionization (DESI).