Over the past decade, the technical requirements of analytical instrumentation have continuously risen driven by the demand for increasingly complex and demanding applications. TOFWERK, a Swiss company with the headquarters in Thun, has been at the forefront of this development by producing modular and ruggedized Time-Of-Flight Mass Spectrometers (TOFMS). They are often used to replace quadrupole mass analysers with more powerful TOF mass analysers. Starting with first customers in atmospheric sciences, TOFWERK TOFMS are now used across a wide range of research areas and lately also in industry. Here we present an overview of mobile applications in which Tofwerk TOFMS are in operation while moved around in space.

This work describes a novel mass spectrometer coupled to gas chromatography (GC-MS) that simultaneously displays the mass spectral information of electron (EI)- and chemical ionization (CI)-generated ion populations for a single chromatographic peak. After GC separation, the eluent is equally split and supplied in parallel to an EI and a novel CI source, both operating continuously. Precise switching of the ion optics provides the exact timing to consecutively extract the respective ion population from both sources and transfer them into a time-of-flight (TOF) mass analyzer. This technique enables the acquisition of complementary information from both ion populations (EI and CI) within a single chromatographic run and with sufficient data points to retain the chromatographic fidelity. The carefully designed GC transfer setup, fast ion optical switching, and synchronized TOF data acquisition system provide an automatic and straightforward spectral alignment of two ion populations. With an eluent split ratio of about 50% between the two ion sources, instrument detection limits of <40 fg on the column (octafluoronaphthalene) for the EI and <2 pg (benzophenone) for the CI source were obtained. The system performance and the additional analytical value for compound identification are demonstrated by means of different common GC standard mixtures and a commercial perfume sample of unknown composition.

2,4,6-Trichloroanisole (TCA) contamination of wine determines huge economic losses for the wine industry estimated to amount to several billion dollars yearly. Over 50 years of studies have determined that this problem is often caused by TCA contamination of the cork stopper, which releases TCA into the wine. The human threshold for TCA is extremely low. A wine contaminated by 1-2 ng/L TCA can be perceived as tainted. Contaminations with <0.5 ng/L TCA are commonly considered negligible and are not perceivable. The possibility of prescreening cork stoppers for TCA contamination would be an enormous advantage. Therefore, the demand for a fast, nondestructive method capable of quantifying the TCA contamination in cork stoppers is impelling. Vastly used analytical methods have so far struggled to provide a fast and reliable solution, whereas sensory analysis by trained panelists is expensive and time-consuming. Here we propose a novel approach based on chemical ionization-time-of-flight (CI-TOF) mass spectrometry employing the "Vocus" ion source and ion-molecule reactor. The technique proved capable of nondestructively quantifying TCA contamination in a single cork stopper in 3 s, with a limit of quantification below the perception threshold. A real test on the industrial scale, quantifying TCA contamination in more than 10000 cork stoppers in a few hours is presented, representing the largest data set of TCA analysis on cork stoppers within the literature and proving the possibility to apply the technique in an industrial environment. The correlation with standard methods for releasable TCA quantification is also discussed.

In September 2017, we conducted a proton-transfer-reaction mass-spectrometry (PTR-MS) intercomparison campaign at the CESAR observatory, a rural site in the central Netherlands near the village of Cabauw. Nine research groups deployed a total of 11 instruments covering a wide range of instrument types and performance. We applied a new calibration method based on fast injection of a gas standard through a sample loop. This approach allows calibrations on timescales of seconds, and within a few minutes an automated sequence can be run allowing one to retrieve diagnostic parameters that indicate the performance status. We developed a method to retrieve the mass-dependent transmission from the fast calibrations, which is an essential characteristic of PTR-MS instruments, limiting the potential to calculate concentrations based on counting statistics and simple reaction kinetics in the reactor/drift tube. Our measurements show that PTR-MS instruments follow the simple reaction kinetics if operated in the standard range for pressures and temperature of the reaction chamber (i.e. 1–4 mbar, 30–120∘, respectively), as well as a reduced field strength E∕N in the range of 100–160 Td. If artefacts can be ruled out, it becomes possible to quantify the signals of uncalibrated organics with accuracies better than ±30 %. The simple reaction kinetics approach produces less accurate results at E∕N levels below 100 Td, because significant fractions of primary ions form water hydronium clusters. Deprotonation through reactive collisions of protonated organics with water molecules needs to be considered when the collision energy is a substantial fraction of the exoergicity of the proton transfer reaction and/or if protonated organics undergo many collisions with water molecules.

Atmospheric oxidation is an important phenomenon which produces large quantities of low-volatility compounds such as sulfuric acid and oxidized organic compounds. Such species may be involved in the nucleation of particles and enhance their subsequent growth to reach the size of cloud condensation nuclei (CCN). In this study, we investigate α-pinene, the most abundant monoterpene globally, and its oxidation products formed through ozonolysis in the Cosmic Leaving OUtdoor Droplets (CLOUD) chamber at CERN (the European Organization for Nuclear Research). By scavenging hydroxyl radicals (OH) with hydrogen (H2), we were able to investigate the formation of highly oxygenated molecules (HOMs) purely driven by ozonolysis and study the oxidation of sulfur dioxide (SO2) driven by stabilized Criegee intermediates (sCIs). We measured the concentrations of HOM and sulfuric acid with a chemical ionization atmospheric-pressure interface time-of-flight (CI-APi-TOF) mass spectrometer and compared the measured concentrations with simulated concentrations calculated with a kinetic model. We found molar yields in the range of 3.5–6.5 % for HOM formation and 22–32 % for the formation of stabilized Criegee intermediates by fitting our model to the measured sulfuric acid concentrations. The simulated time evolution of the ozonolysis products was in good agreement with measured concentrations except that in some of the experiments sulfuric acid formation was faster than simulated. In those experiments the simulated and measured concentrations met when the concentration reached a plateau but the plateau was reached 20–50 min later in the simulations. The results shown here are consistent with the recently published yields for HOM formation from different laboratory experiments. Together with the sCI yields, these results help us to understand atmospheric oxidation processes better and make the reaction parameters more comprehensive for broader use.

We evaluate the performance of a new chemical ionization source called Vocus, consisting of a discharge reagent-ion source and focusing ion-molecule reactor (FIMR) for use in protontransfer-reaction time-of-flight mass spectrometry (PTR-TOF) measurements of volatile organic compounds (VOCs) in air. The reagent ion source uses a low-pressure discharge. The FIMR consists of a glass tube with a resistive coating, mounted inside a radio-frequency (RF) quadrupole. The axial electric field is used to enhance ion collision energies and limit cluster ion formation. The RF field focuses ions to the central axis of the reactor and improves the detection efficiency of product ions. Ion trajectory calculations demonstrate the mass-dependent focusing of ions and enhancement of the ion collision energy by the RF field, in particular for the lighter ions. Product ion signals are increased by a factor of 10 when the RF field is applied (5,000-18,000 cps ppbv-1), improving measurement precision and detection limits while operating at very similar reaction conditions as traditional PTR instruments. Due to the high water mixing ratio in the FIMR, we observe no dependence of the sensitivity on ambient sample humidity. In this work, the Vocus is interfaced to a TOF mass analyzer with a mass resolving power up to 14,000, which allows clear separation of isobaric ions, observed at nearly every nominal mass when measuring ambient air. Measurement response times are determined for a range of ketones with saturation vapor concentrations down to 5×104 μg m-3 and compare favorably with previously published results for a PTR-MS instrument.

Abstract. It was recently shown by the CERN CLOUD experiment that biogenic highly oxygenated molecules (HOMs) form particles under atmospheric conditions in the absence of sulfuric acid, where ions enhance the nucleation rate by 1–2 orders of magnitude. The biogenic HOMs were produced from ozonolysis of α -pinene at 5  ∘ C. Here we extend this study to compare the molecular composition of positive and negative HOM clusters measured with atmospheric pressure interface time-of-flight mass spectrometers (APi-TOFs), at three different temperatures (25, 5 and − 25  ∘ C). Most negative HOM clusters include a nitrate (NO 3 - ) ion, and the spectra are similar to those seen in the nighttime boreal forest. On the other hand, most positive HOM clusters include an ammonium (NH 4 + ) ion, and the spectra are characterized by mass bands that differ in their molecular weight by ∼  20 C atoms, corresponding to HOM dimers. At lower temperatures the average oxygen to carbon (O : C) ratio of the HOM clusters decreases for both polarities, reflecting an overall reduction of HOM formation with decreasing temperature. This indicates a decrease in the rate of autoxidation with temperature due to a rather high activation energy as has previously been determined by quantum chemical calculations. Furthermore, at the lowest temperature ( − 25  ∘ C), the presence of C 30  clusters shows that HOM monomers start to contribute to the nucleation of positive clusters. These experimental findings are supported by quantum chemical calculations of the binding energies of representative neutral and charged clusters.

Introduction Classical drift tube ion mobility methods suffer from low sensitivity due to the narrow gate necessary for useful mobility resolution. Multiplexing methods such as Fourier or Hadamard transforms can theoretically resolve this dilemma, but have been problematic in practice. We report on development of a multiplexing strategy which achieves the desired performance in routine use. It has been implemented in a compact IMS-TOFMS instrument, including post-IMS collisional activation for structural elucidation.

This chapter contains sections titled: Introduction Thin and Thick Layers: A Tentative Definition What Specific Information MS Techniques could Bring to thin and thick Films Analysis Compared to other Techniques? Main MS Techniques Applied to Thin/Thick Films Time of Sputtering/Speed of Acquisition Trade-Off Differences in Sputtering/Ionization Mechanisms between SIMS and GD-MS Pulse Shapes and how to Best Use Temporal Information for Pulsed Glow Discharge Mass Spectrometry Measurement and Data Interpretation in GD-TOFMS Practical Examples Conclusions List of Abbreviations References

Understanding the composition of complex hydrocarbon mixtures is important for environmental studies in a variety of fields, but many prevalent compounds cannot be confidently identified using traditional gas chromatography/mass spectrometry (GC/MS) techniques. This work uses vacuum-ultraviolet (VUV) ionization to elucidate the structures of a traditionally "unresolved complex mixture" by separating components by GC retention time, t(R), and mass-to-charge ratio, m/z, which are used to determine carbon number, N(C), and the number of rings and double bonds, N(DBE). Constitutional isomers are resolved on the basis of t(R), enabling the most complete quantitative analysis to date of structural isomers in an environmentally relevant hydrocarbon mixture. Unknown compounds are classified in this work by carbon number, degree of saturation, presence of rings, and degree of branching, providing structural constraints. The capabilities of this analysis are explored using diesel fuel, in which constitutional isomer distribution patterns are shown to be reproducible between carbon numbers and follow predictable rules. Nearly half of the aliphatic hydrocarbon mass is shown to be branched, suggesting branching is more important in diesel fuel than previously shown. The classification of unknown hydrocarbons and the resolution of constitutional isomers significantly improves resolution capabilities for any complex hydrocarbon mixture.

We describe a new instrument, chemical ionization (CI) high-resolution time-of-flight mass spectrometer (ToFMS) coupled to a micro-orifice volatilization impactor (MOVI-HRToF-CIMS). The MOVI-HRToF-CIMS instrument is unique in that, within a compact field-deployable package, it provides (1) quantifiable molecular-level information for both gas and particle-phase organic species on timescales ranging from ≤1 s for gases to 10–60 min for particle-phase compounds that can be used to efficiently probe oxidation and secondary organic aerosol (SOA) formation mechanisms, and (2) relative volatility information of the detected compounds simultaneously estimated using the programmed thermal desorption information obtained from the MOVI. We demonstrate the capabilities of a prototype instrument using known test compounds and complex mixtures generated from the oxidation of biogenic and anthropogenic hydrocarbons. We present spectra obtained using both negative and positive ion CI with acetate (CH3C(O)O−) and protonated water clusters (H3O+·(H2O) n ), respectively, as reagent ions. The instrument has high mass resolving power (R = 5000 above m/Q 250 Th) and mass accuracy (±20 ppm) enabling estimation of compound elemental composition. Instrument sensitivity in negative ion mode was tested using formic acid as a representative gas-phase compound, and that for particle-phase compounds was tested using palmitic, azelaic, and tricarballylic acids. With a heated MOVI inlet, an ion count rate of ∼15 Hz is achieved when sampling 1 pptv (= 1 pmol/mol) of formic acid (or other monocarboxylic acids) under typical operating conditions. This sensitivity translates to detection limits less than 1 ng/m3 for carboxylic acids in the particle-phase. We also discuss the remaining challenges with this instrument to broadly characterizing gaseous and particulate oxygenated organic compounds in situ. Copyright 2012 American Association for Aerosol Research

This work describes the realization of rapid switching between hard electron ionization (EI) and soft single-photon ionization (SPI) integrated in a compact orthogonal acceleration time-of-flight mass spectrometer. Vacuum-ultraviolet (VUV) photons of 9.8 eV (126 nm) emitted from the innovative electron-beam-pumped rare-gas excimer light source (EBEL) filled with argon are focused into the ion chamber by an ellipsoidal mirror optic for accomplishing of SPI. This novel orthogonal acceleration time-of-flight mass spectrometer with switching capability was hyphenated to one-dimensional gas chromatography (GC) and comprehensive two-dimensional (2D) gas chromatography (GC × GC) for the first time. Within this demonstration study, a maximum switching frequency of 80 Hz was applied for investigation of a mineral-oil-type diesel sample. This approach allows the quasi-simultaneous acquisition of complementary information about the fragmentation pattern (EI) as well as the molecular mass (SPI) of compounds within a single analysis. Furthermore, by application of a polar GC column for separation, the SPI data can be displayed in a 2D contour plot, leading to a comprehensive 2D characterization (GC × MS), whereas the typical group-type assignment for diesel is also met.

Increasing the dimensionality of an analysis enables more detailed and comprehensive investigations of complex mixtures. One dimensional separation techniques like gas chromatography (GC) and ion mobility spectrometry (IMS) provide limited chemical information about complex mixtures. The combination of GC, ion mobility spectrometry, and time-of-flight mass spectrometry (GC-IM-TOFMS) provides three-dimensional separation of complex mixtures. In this work, a hybrid GC-IM-TOFMS with a secondary electrospray ionization (SESI) source provided four types of analytical information: GC retention time, ion mobility drift time, mass-to-charge ratios, and ion intensity. The use of secondary electrospray ionization enables efficient and soft ionization of gaseous sample vapors at atmospheric pressure. Several complex mixtures, including lavender and peppermint essential oils, were analyzed by GC-SESI-IM-TOFMS. The resulting 3D data from these mixtures, each containing greater than 50 components, were plotted as 3D projections. In particular, post-processed data plotted in three dimensions showed that many mass selected GC peaks were resolved into different ion mobility peaks. This technique shows clear promise for further in-depth analyses of complex chemical and biological mixtures.

The time-of-flight aerosol mass spectrometer (ToF-AMS) determines particle size by measuring velocity after expansion into vacuum and analyzes chemical composition by thermal vaporization and electron ionization mass spectrometry (MS). Monitoring certain dynamic processes requires the ability to track changes in aerosol chemistry and size with sub-second time resolution. We demonstrate a new ToF-AMS data acquisition mode capable of collecting high-resolution aerosol mass spectra at rates exceeding 1kHz. Coupled aerosol size and MS measurements can be made at approximately 20Hz. These rates are about 1/10 of the physically meaningful limits imposed by the ToF-AMS detection processes. The fundamentals of the time-of-flight MS (TOFMS) data acquisition system are described and characterized with a simple algebraic model. Derived expressions show how improvements in data acquisition and computer hardware will translate into rates approaching the physical limits. Conclusions regarding limits of performance can be extended to other TOFMS that use analog signal detection in a high-speed application outside of aerosol science. The high-speed acquisition mode of the ToF-AMS enables speciated aerosol eddy covariance flux measurements, which demand precise, 10-Hz synchronization of the MS with a sonic anemometer. Flux data acquired over a forest during the BEARPEX-1 campaign are presented as an example of this new technique. For aircraft measurements, faster acquisition translates to higher spatial resolution, which is demonstrated with data from the recent NASA ARCTAS field campaign in Alaska. Finally, the fast acquisition mode is used to measure the rapid fluctuations in particle emissions of a controlled biomass burn during from the FLAME-2 experiment. To our knowledge this is currently the fastest system for acquisition of chemically resolved aerosol data.

The design of a new ion mobility mass spectrometer (IM-MS) is presented. This new design features an ambient-pressure resistive glass ion mobility drift tube (RGIMS) coupled to a high-resolution time-of-flight mass spectrometer (TOFMS) by an enhanced interface that includes two segmented quadrupoles. The interface design demonstrates an increase in sensitivity while maintaining high resolving power typically achieved for ambient-pressure IMS drift tubes. Performance of the prototype instrument was evaluated and the analytical figures of merit for standard solutions as well as complex samples such as human blood were determined. For a 3 μM solution of caffeine, the peak was collected in 36 s and gave a response of 10 counts/s. The detection limit (defined as 1 count/s) was calculated to be 300 nM concentration of caffeine from the response rate from the 36 s run. Controlled fragmentation of caffeine was achieved through adjustment of voltages applied on the interface lenses. Over 300 tentative metabolites were detected in human blood along with 80 isomers/isobars with ion counts >5. Isotope ratios from extracted mass spectra of selected mobility peaks were used to identify selected metabolite compounds. High separation power for both IMS (resolving power, t(d)/Δt(w1/2), was 85) and MS (mass resolving power, m/Δm, maximum was 7000 with a mass accuracy between 2 and 10 ppm) was measured. Developed software for data acquisition, control and display allowed flexibility in instrument control, data evaluation and visualization.

One- and comprehensive two-dimensional gas chromatography were hyphenated with soft photoionization mass spectrometry. The characteristics of these two- and three-dimensional comprehensive separation techniques are discussed in detail. Using the innovative electron beam pumped excimer light source (EBEL) for single-photon ionization (SPI), organic molecules with ionization energies (E ( i )) of below 9.8 eV can be detected by a time-of-flight mass spectrometer (TOF-MS). SPI with 126 nm vacuum ultraviolet (VUV) photons enables the universal and soft ionization of organic molecules. SPI-TOF-MS hyphenated to one-dimensional gas chromatography results in a comprehensive two-dimensional separation method (GCxMS). To demonstrate this, diesel fuel was analyzed, and the resulting GCxMS chromatograms are discussed in depth. A three-dimensional separation method was also realized by combining comprehensive two-dimensional gas chromatography (GCxGC) with SPI-MS. In the resulting separation space, constituents originating from mineral oil diesel blended with biodiesel were dispersed along the two GC separation axes, while the molecular mass axis served as a third separation dimension.