Flowing Atmospheric Pressure Afterglow for Ambient Ionization: Reaction Pathways Revealed by Modeling

Aghaei, Maryam; Bogaerts, Annemie

doi:10.1021/acs.analchem.0c04076

Cited by 7 publications

(8 citation statements)

References 57 publications

(155 reference statements)

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“…This is supported by recent modelling from the Bogaerts laboratory, which also identified reactive N O and O 3 neutral species in the afterglow [99]. The production of protonated water clusters by nitrogen dimer ions is favourable due to the high dipole moment and low ionization potential of water despite the water's low molar concentration in air.…”

Section: Discussion and Summarysupporting

confidence: 56%

Development and application of a novel mass spectrometry ionization source for biological chemistry

Owen¹

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Since its development, electrospray ionization (ESI) for the analysis of thermally labile, polar compounds and particularly biomolecules has been extremely useful. Not all compounds can be easily protonated and electron ionization (EI) is still a widely used ionization method for compounds like hydrocarbons. However, the low-pressure environment of the EI source requires complex and expensive vacuum systems and inlets. Therefore, a source which can ionises non-polar compounds while operating at atmospheric pressure would be highly advantageous. In this thesis I have undertaken development and characterisation of four prototype atmospheric pressure glow discharge ionization sources for the analysis of compounds not normally amiable to ionization by conventional atmospheric pressure ionization sources. A helium micro-glow discharge source (“Prototype V”) operated using a direct current power supply was studied and its discharge characterised. Its current-voltage relationship increased linearly which is typical of the abnormal glow regime while thermal imaging showed it had a “cold” discharge. Prototype V was successfully interfaced with a Xevo G2-S time-of-ﬂight and a Xevo TQ-S triple quadrupole (Waters Corp, Wilmslow, UK) and used with a range of sample introduction methods, initially a solids probe, but later APCI and ESI probes. These probes enabled prototype V to readily integrate with separation sciences; speciﬁcally liquid chromatography was demonstrated for complex mixture analysis. Prototype V exhibited high analytical sensitivity in the nanogram range in both positive and negative modes and could ionize a wide range of compound chemistries from polar to non-polar. In particular it showed sensitivity to non-polar compounds in negative-ion mode when compared to ESI. This gives the source the potential to operate in conjunction with a range of sample inlets and in combination with other ionization techniques as part of a multimodal platform to analyse the widest range of samples and a step towards a universal source.

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Section: Discussion and Summarysupporting

confidence: 56%

Development and application of a novel mass spectrometry ionization source for biological chemistry

Owen¹

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“…The model used herein accounted for 58 species and 739 reactions that revolved around the He, H and O products produced in a typical He/H 2 O plasma. The relevant reactions were taken from a previous study by Aghaei and Bogaerts [58], however no N containing reactions were included since high purity He (99.999%) was used throughout, and the capillary outlet is submerged and isolated from air. Rate equations, if not constant, are calculated using electron/gas temperature dependent reaction rates from literature and are integrated in time using the built-in solver.…”

Section: Methodsmentioning

confidence: 99%

Generation and delivery of free hydroxyl radicals using a remote plasma

McQuaid

Rutherford

Mariotti

et al. 2023

Plasma Sources Sci. Technol.

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We demonstrate a new gas-based OH• generation source using a low power RF-driven atmospheric pressure plasma configured to deliver the radical flux into the far effluent region, well away from interference from other plasma factors such as electric fields, currents, and UV radiation. Using He – H2O gas chemistry isolated from the laboratory air, the plasma generated flux contains OH• and other radicals including H•, O and HO2 as well as H2O2 which, along with OH•, was found to vary with H2O vapour content and absorbed power density. Peak flux values were 2.3 nmol s-1 and 0.23 nmol s-1 for H2O2 and OH• respectively at a distance of 50 mm from the plasma, with 790 ppmv H2O and a power density of ~ 108 W m-3. The maximum OH• flux density was 4.5 x 1019 m-2 s-1 falling to 1.7 x 1019 m-2 s-1 at 110 mm, equivalent to generation rates of 74 mM s-1 and 28 mM s-1. Despite high OH• recombination rates at the plasma exit, the escaping flux is still significant, indicating a viable delivery capability to downstream targets. Its performance with regard to OH• generation rates compares well with traditional OH• generation techniques such as radiolysis, advanced oxidation processes and enhanced Fenton-chemistry approaches where OH• production rates are sub-mM s-1. Delivering precisely quantifiable OH• fluxes provides new opportunities for scientific studies and technological opportunities in cell biology, atmospheric chemistry, protein unfolding and systematic dose studies for plasma-based and other OH• related potential medical treatments.

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“…Briefly, because of the various favorable associative ionization and conversion rates, [25][26][27] He 2 + has a greater population density than that of He + in He-based plasmas operated at pressures >5 torr. 28,29 Modeling studies on a DBD at atmospheric pressure 30 and a helium-flowing atmospheric pressure afterglow 31 showed that the He 2 + population is at least one order of magnitude larger than that of He + . One decay pathway for the He 2 + ion is through direct ion-electron dissociative recombination, yielding He* as a product.…”

Section: Two-dimensional Images Of Steady-state Ltp Emissionmentioning

confidence: 99%

Characterization of a Low-Temperature Plasma (LTP) Ambient Ionization Source Using Temporally Resolved Monochromatic Imaging Spectrometry

Chan,

Engelhard,

Wiley

et al. 2023

Appl Spectrosc

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The low-temperature plasma (LTP) probe is a common plasma-based source used for ambient desorption–ionization mass spectrometry (MS). While the LTP probe has been characterized in detail with MS, relatively few studies have used optical spectroscopy. In this paper, two-dimensional (2D) imaging at selected wavelengths is used to visualize important species in the LTP plasma jet. First, 2D steady-state images of the LTP plume for N2+ (391.2 nm), He I (706.5 nm), and N2 (337.1 nm) emissions were recorded under selected plasma conditions. Second, time-resolved 2D emission maps of radiative species in the LTP plasma jet were recorded through the use of a 200 ns detection gate and varying gate delays with respect to the LTP trigger pulse. Emission from He I, N2+, and N2 in the plasma jet region was found to show a transient behavior (often referred to as plasma bullets) lasting only a few microseconds. The N2+ and He I maps were highly correlated in spatial and temporal structure. Further, emission from N2 showed two maxima in time, one before and one after the maximum emission for N2+ and He I, due to an initial electronic excitation wave and ion–electron recombination, respectively. Third, the interaction of the LTP probe with a sample substrate and an electrically grounded metallic needle was studied. Emission from a fluorophore on the sample substrate showed an initial photon-induced excitation from plasma-generated photons followed by electronic excitation by other plasma species. The presence of a grounded needle near the plasma jet significantly extended the plasma jet lifetime and also generated a long-lived corona discharge on the needle. The effect of LTP operating parameters on emission spectra was correlated with mass-spectral results including reagent-ion signals. Lastly, five movies provide a side-by-side comparison of the temporal behavior of emitting species and insights into the interactions of the emission clouds with a sample surface as well as an external needle. Temporally and spatially resolved imaging provided insights into important processes in the LTP plasma jet, which will help improve analyte ion sampling in LTP–MS.

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Flowing Atmospheric Pressure Afterglow for Ambient Ionization: Reaction Pathways Revealed by Modeling

Cited by 7 publications

References 57 publications

Development and application of a novel mass spectrometry ionization source for biological chemistry

Development and application of a novel mass spectrometry ionization source for biological chemistry

Generation and delivery of free hydroxyl radicals using a remote plasma

Characterization of a Low-Temperature Plasma (LTP) Ambient Ionization Source Using Temporally Resolved Monochromatic Imaging Spectrometry

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