Effect of internal and external conditions on ionization processes in the FAPA ambient desorption/ionization source

Orejas, Jaime; Pfeuffer, Kevin P.; Ray, Steven J.; Pisonero, Jorge; Sanz‐Medel, Alfredo; Hieftje, Gary M.

doi:10.1007/s00216-014-8088-x

Cited by 20 publications

(27 citation statements)

References 41 publications

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“…DART used a different interface with the ion inlet and produced lower water cluster ion signal than FAPA. Similarly, water cluster variance with humidity differed slightly from previous observations with different experimental conditions and entrance optics [24]. The proton affinity of a water cluster increases with size (n = 1, 696 kJ/mol; n = 2, 833 kJ/ mol; n = 3, 889 kJ/mol; n = 4, 920 kJ/mol; etc.)…”

Section: Resultscontrasting

confidence: 60%

“…Significant changes in molecular adduct ion signal abundance especially impair trace detection and quantitation or MS/MS ion statistics. One solution is to indirectly control humidity by elevating discharge temperature so that humidity effects are diminished without also causing excessive fragmentation [24]. However, differing energetics would require empirical study to find an optimal temperature balance for each analyte, a complication to the rapid, simple analyses that characterize postplasma ADI sources.…”

Section: Discussionmentioning

confidence: 99%

“…Large effects on mass spectra were also observed with DART of one analyte in a range of humidity values [23]. Humidity effects on another post-plasma ADI source, flowing atmospheric pressure afterglow (FAPA) ionization, were examined using saturated salt solutions to humidify nitrogen (or argon) in a cell sealing the FAPA directly to the mass spectrometer inlet [24]. However, most ADI analysis is performed with the post-plasma probe mounted in open laboratory air in front of the MS inlet (i.e., not a chemically modified atmosphere enclosure).…”

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confidence: 99%

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Humidity Effects on Fragmentation in Plasma-Based Ambient Ionization Sources

Newsome

Ackerman

Johnson³

2015

J. Am. Soc. Mass Spectrom.

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Abstract. Post-plasma ambient desorption/ionization (ADI) sources are fundamentally dependent on surrounding water vapor to produce protonated analyte ions. There are two reports of humidity effects on ADI spectra. However, it is unclear whether humidity will affect all ADI sources and analytes, and by what mechanism humidity affects spectra. Flowing atmospheric pressure afterglow (FAPA) ionization and direct analysis in real time (DART) mass spectra of various surface-deposited and gas-phase analytes were acquired at ambient temperature and pressure across a range of observed humidity values. A controlled humidity enclosure around the ion source and mass spectrometer inlet was used to create programmed humidity and temperatures. The relative abundance and fragmentation of molecular adduct ions for several compounds consistently varied with changing ambient humidity and also were controlled with the humidity enclosure. For several compounds, increasing humidity decreased protonated molecule and other molecular adduct ion fragmentation in both FAPA and DART spectra. For others, humidity increased fragment ion ratios. The effects of humidity on molecular adduct ion fragmentation were caused by changes in the relative abundances of different reagent protonated water clusters and, thus, a change in the average difference in proton affinity between an analyte and the population of water clusters. Control of humidity in ambient post-plasma ion sources is needed to create spectral stability and reproducibility.

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Section: Resultscontrasting

confidence: 60%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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Humidity Effects on Fragmentation in Plasma-Based Ambient Ionization Sources

Newsome

Ackerman

Johnson³

2015

J. Am. Soc. Mass Spectrom.

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“…[23][24][25] Accordingly, discontinuous helium ow affects the sample temperature and results in changes in sensitivity. [23][24][25] Accordingly, discontinuous helium ow affects the sample temperature and results in changes in sensitivity.…”

Section: Effect On Sample Temperaturementioning

confidence: 99%

Helium conservation by discontinuous introduction in the flowing atmospheric-pressure afterglow source for ambient desorption-ionization mass spectrometry

Storey

Zeiri

Ray

et al. 2015

J. Anal. At. Spectrom.

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As helium availability declines in many parts of the world and helium prices rise, it is desirable to limit helium use by plasma-based sources for ambient desorption-ionization mass spectrometry (ADI-MS). Here, helium flow to the flowing atmospheric-pressure afterglow (FAPA) source is interrupted to reduce total helium consumption. The FAPA glow discharge can be sustained for up to several minutes after the helium flow is halted, without damaging the source. As a result, a stable discharge can be maintained indefinitely by introducing relatively short periods of helium flow just before the discharge extinguishes. When helium flow is restored, the signal rises and reaches a steady state after 20 s; signal integration after this time yields mass spectra that are very similar, sensitivities that are 71% of those under continuous-flow conditions, and comparable precision.

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“…25 In this context, the influence of these parameters on the measured mobility spectra associated with the reactant ions was investigated. Fig.…”

Section: Resultsmentioning

confidence: 99%

A flowing atmospheric pressure afterglow as an ion source coupled to a differential mobility analyzer for volatile organic compound detection

Bouza

Orejas

López-Vidal

et al. 2016

Analyst

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Atmospheric pressure glow discharges have been widely used in the last decade as ion sources in ambient mass spectrometry analyses. Here, an in-house flowing atmospheric pressure afterglow (FAPA) has been developed as an alternative ion source for differential mobility analysis (DMA). The discharge source parameters (inter-electrode distance, current and helium flow rate) determining the atmospheric plasma characteristics have been optimized in terms of DMA spectral simplicity with the highest achievable sensitivity while keeping an adequate plasma stability and so the FAPA working conditions finally selected were: 35 mA, 1 L min(-1) of He and an inter-electrode distance of 8 mm. Room temperature in the DMA proved to be adequate for the coupling and chemical analysis with the FAPA source. Positive and negative ions for different volatile organic compounds were tested and analysed by FAPA-DMA using a Faraday cup as a detector and proper operation in both modes was possible (without changes in FAPA operational parameters). The FAPA ionization source showed simpler ion mobility spectra with narrower peaks and a better, or similar, sensitivity than conventional UV-photoionization for DMA analysis in positive mode. Particularly, the negative mode proved to be a promising field of further research for the FAPA ion source coupled to ion mobility, clearly competitive with other more conventional plasmas such as corona discharge.

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Effect of internal and external conditions on ionization processes in the FAPA ambient desorption/ionization source

Cited by 20 publications

References 41 publications

Humidity Effects on Fragmentation in Plasma-Based Ambient Ionization Sources

Humidity Effects on Fragmentation in Plasma-Based Ambient Ionization Sources

Helium conservation by discontinuous introduction in the flowing atmospheric-pressure afterglow source for ambient desorption-ionization mass spectrometry

A flowing atmospheric pressure afterglow as an ion source coupled to a differential mobility analyzer for volatile organic compound detection

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