Computational model of a direct current glow discharge used as an ambient desorption/ionization source for mass spectrometry

Ellis, Wade C.; Spencer, Ross L.; Reininger, Charlotte; Farnsworth, Paul B.

doi:10.1039/c7ja00242d

Cited by 4 publications

(4 citation statements)

References 41 publications

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“…In contrast, charge transfer reagent species were most abundant at low gas flow rates (0.5 L/min) and high discharge currents (30 mA). Considering the extreme cases of 0.5 L/min and 30 mA, or 1.5 L/min and 5 mA, while the condition used in our study (1.5 L/min and 25 mA) is more intermediate and is reported as a typical operating condition of the FAPA source, we may indeed expect to have both PT and CT reagent ions.…”

Section: Resultsmentioning

confidence: 99%

“…This yields ca. 11.25 W applied power, as reported in both experimental and computational studies for a typical FAPA source. , The helium gas can flow out of the discharge cell through an orifice with 1 mm diameter in the center of the disk electrode. Details of the geometry and operating conditions are summarized in Table S1 in the Supporting Information (SI).…”

Section: Model Descriptionmentioning

confidence: 99%

“…40 This study was focused on the discharge region and did not include the afterglow, characteristic for the FAPA. Ellis et al presented a 2D fluid model for a helium DC glow discharge in a mixture of N 2 and H 2 O used for ADI-MS. 41 Both the fluid dynamics of the flowing gases and the chemical kinetics were described, considering 16 species interacting in 40 reactions. The authors showed that changes in impurity levels of the He gas (due to N 2 and H 2 O) had a large effect on the formation of water clusters.…”

Section: ■ Introductionmentioning

confidence: 99%

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

Aghaei

Bogaerts

2021

Anal. Chem.

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We describe the plasma chemistry in a helium flowing atmospheric pressure afterglow (FAPA) used for analytical spectrometry, by means of a quasi-one-dimensional (1D) plasma chemical kinetics model. We study the effect of typical impurities present in the feed gas, as well as the afterglow in ambient humid air. The model provides the species density profiles in the discharge and afterglow regions and the chemical pathways. We demonstrate that H, N, and O atoms are formed in the discharge region, while the dominant reactive neutral species in the afterglow are O3 and NO. He* and He2* are responsible for Penning ionization of O2, N2, H2O, H2, and N, and especially O and H atoms. Besides, He2 + also contributes to ionization of N2, O2, H2O, and O through charge transfer reactions. From the pool of ions created in the discharge, NO+ and (H2O)3H+ are the dominant ions in the afterglow. Moreover, negatively charged clusters, such as NO3H2O– and NO2H2O–, are formed and their pathway is discussed as well. Our model predictions are in line with earlier observations in the literature about the important reagent ions and provide a comprehensive overview of the underlying pathways. The model explains in detail why helium provides a high analytical sensitivity because of high reagent ion formation by both Penning ionization and charge transfer. Such insights are very valuable for improving the analytical performance of this (and other) ambient desorption/ionization source(s).

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Section: Resultsmentioning

confidence: 99%

Section: Model Descriptionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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

Aghaei

Bogaerts

2021

Anal. Chem.

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“…Through modeling studies, 25,39 the He 2 + ion was identified as one of the key species for ADI-MS ionization; it yields N 2 + and H 2 O + , which are important primary reagent ions leading to the formation of protonated water-cluster ions (i.e., [H 2 O] n H + ) that are in turn responsible for proton transfer ionization. The closeness in the behavior of He and N 2 + emission is clear in Fig.…”

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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Modeling plasmas in analytical chemistry—an example of cross-fertilization

Bogaerts

2020

Anal Bioanal Chem

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Computational model of a direct current glow discharge used as an ambient desorption/ionization source for mass spectrometry

Abstract: A new model of a plasma ionization source anchored by experimental data giving a comprehensive view of the discharge mechanism.

Cited by 4 publications

References 41 publications

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

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

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

Modeling plasmas in analytical chemistry—an example of cross-fertilization

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