Atmospheric pressure photoionization mechanisms. 2. The case of benzene and toluene

Tubaro, Michela; Marotta, Ester; Seraglia, Roberta; Traldi, Pietro

doi:10.1002/rcm.1208

Cited by 74 publications

(92 citation statements)

References 16 publications

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“…This is very important because O 2 Ϫ· possesses the strongest gas-phase basicity of all background ions, as shown in Table 1, when toluene was exclusively used as both the solvent and dopant. The existence of other nonatmospheric gas ions in Figure 1 can possibly be interpreted through gas-phase reactions as previously reported by Traldi and coworkers [20]. However, we were unable to assign the m/z 212.0735 and 255.2310 ions probable chemical structures.…”

Section: Figuresupporting

confidence: 60%

Negative ion-atmospheric pressure photoionization: Electron capture, dissociative electron capture, proton transfer, and anion attachment

Song

Wellman

Yao

et al. 2007

J. Am. Soc. Mass Spectrom.

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To better guide the development of liquid chromatography/electron capture-atmospheric pressure photoionization-mass spectrometry (LC/EC-APPI-MS) in analysis of low polarity compounds, the ionization mechanism of 19 compounds was studied using dopant assisted negative ion-APPI. Four ionization mechanisms, i.e., EC, dissociative EC, proton transfer, and anion attachment, were identified as being responsible for the ionization of the studied compounds. The mechanisms were found to sometimes compete with each other, resulting in multiple ionization products from the same molecule. However, dissociative EC and proton transfer could also combine to generate the same [M Ϫ H] Ϫ ions. Experimental evidence suggests that O 2 Ϫ· , which was directly observed in the APPI source, plays a key role in the formation of [M Ϫ H] Ϫ ions by way of proton transfer. Introduction of anions more basic than O 2 Ϫ· , i.e., C 6 H 5 CH 2 Ϫ , into the APPI source, via addition of di-tert-butyl peroxide in the solvent and/or dopant, i.e., toluene, enhanced the deprotonation ability of negative ion-APPI. Although the use of halogenated solvents could hinder efficient EC, dissociative EC, and proton transfer of negative ion-APPI due to their EC ability, the subsequently generated halide anions promoted halide attachment to compounds that otherwise could not be efficiently ionized. With the four available ionization mechanisms, it becomes obvious that negative ion-APPI is capable of ionizing a wider range of compounds than negative ion chemical ionization (NICI), negative ion-atmospheric pressure chemical ionization (negative ion-APCI) or negative ion-electrospray ionization (negative ion-ESI). (J Am Soc Mass Spectrom 2007, 18, 1789 -1798) © 2007 American Society for Mass Spectrometry I t is well known that liquid chromatography mass spectrometry (LC/MS) favors the analysis of polar compounds, as acid-base solution reactions are the most commonly observed ionization mechanism when using electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). Traditionally, gas chromatography mass spectrometry (GC/MS) using both electron ionization (EI) and chemical ionization (CI) is employed for the analysis of volatile and thermostable nonpolar compounds. However, it can become difficult to analyze nonvolatile and/or thermo-labile nonpolar compounds via hyphenated techniques of chromatography and MS.In the year 2000, atmospheric pressure photoionization (APPI) [1] was developed as a complement to LC/ESI-MS and LC/APCI-MS. Presently, two fundamentally different APPI sources are commercially available [1,2]. Syagen Technology (Tustin, CA) produces PhotoMate, and Applied Biosystems/MDS SCIEX (Concord, Ontario, Canada) markets PhotoSpray. In both designs, photons emitted by a krypton discharge lamp are used to initiate a series of gas-phase reactions, which finally lead to analyte ionization. However, they differ in that PhotoMate utilizes a design to enhance direct APPI, while PhotoSpray implements a design using a dopant, usually tolu...

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Section: Figuresupporting

confidence: 60%

Negative ion-atmospheric pressure photoionization: Electron capture, dissociative electron capture, proton transfer, and anion attachment

Song

Wellman

Yao

et al. 2007

J. Am. Soc. Mass Spectrom.

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“…Ultrahigh-resolution mass analysis (in this work, m/⌬m 50% ϭ 500,000, in which ⌬m 50% is the mass spectral peak full width at half-maximum peak height) is needed to distinguish various close mass doublets: 13 C versus 12 CH (4.5 mDa), 13 CH versus 12 CD (2.9 mDa), and H 2 versus D (1. A tmospheric pressure photoionization (APPI) forms positive ions through several mechanisms that include proton transfer reactions [1,2]. As for electrospray ionization (ESI), a protic compound must be present in solution or the gas phase to facilitate efficient proton transfer.…”

Section: And [M ϩ D]mentioning

confidence: 99%

Atmospheric pressure photoionization proton transfer for complex organic mixtures investigated by fourier transform ion cyclotron resonance mass spectrometry

Purcell

Hendrickson

Rodgers

et al. 2007

J. Am. Soc. Mass Spectrom.

113

116

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“…The ionization technique is ideal for non-polar aromatic compounds because the photon energy (typically 10 eV) is great enough to ionize aromatics but not nonaromatic solvents. However, direct photoionization is usually not efficient [9]°and°the°addition°of°a°dopant enhances ionization efficiency through proton-transfer reactions and charge-exchange reactions.…”

mentioning

confidence: 99%

Speciation of nitrogen containing aromatics by atmospheric pressure photoionization or electrospray ionization fourier transform ion cyclotron resonance mass spectrometry

Purcell

Rodgers

Hendrickson

et al. 2007

J. Am. Soc. Mass Spectrom.

120

142

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We determine the elemental compositions of aromatic nitrogen model compounds as well as a petroleum sample by atmospheric pressure photoionization (APPI) and electrospray Ionization (ESI) with a 9.4 Tesla Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. From the double-bond equivalents calculated for the nitrogen-containing ions from a petroleum sample, we can infer the aromatic core structure (pyridinic versus pyrrolic nitrogen heterocycle) based on the presence of M ϩ · (odd-electron) versus [MϩH] ϩ (evenelectron) ions. Specifically, nitrogen speciation can be determined from either a single positive-ion APPI spectrum or two ESI (positive-and negative-ion) spectra. APPI operates at comparatively higher temperature than ESI and also produces radical cations that may fragment before detection. However, APPI fragmentation of aromatics can be eliminated by judicious choice of instrumental parameters. [3][4][5][6]. The ionization efficiency correlates with acidity or basicity. For example, carboxylic acids are efficiently ionized by negative-ion ESI, whereas basic species (e.g., pyridinic N 1 species) are efficiently ionized by positive-ion ESI.For non-polar aromatics, atmospheric pressure photoionization [7,8] (APPI) can produce ions from species that are not efficiently ionized by ESI. The youngest of the soft ionization methods, dopant-assisted APPI, was initially developed to interface liquid chromatography to mass spectrometry to analyze simple mixtures. The ionization technique is ideal for non-polar aromatic compounds because the photon energy (typically 10 eV) is great enough to ionize aromatics but not nonaromatic solvents. However, direct photoionization is usually not efficient [9]°and°the°addition°of°a°dopant enhances ionization efficiency through proton-transfer reactions and charge-exchange reactions.Although APPI is considered to be a soft ionization technique (i.e., produces minimal fragmentation of most analytes), it has been considered less soft than ESI because the APPI heated nebulizer and the source region can reach Ͼ300°C, whereas ESI is conducted at room temperature. Furthermore, toluene dopantassisted°APPI°produces°radical°cations°[10]°that°can participate in further gas-phase reactions.Here, we compare ESI and APPI for analysis of petroleum crude oil (chosen because it represents the most complex organic mixture within a dynamic range of 1000 -10,000). The nitrogen atom in aromatic N 1 class species in petroleum can reside in a five-membered ring (pyrrolic) or six-membered ring (pyridinic) and be readily protonated (pyridinic) or deprotonated (pyrrolic) by positive-ion or negative-ion ESI, respectively [11].°However,°positive-ion°APPI°efficiently°generates both pyrrolic and pyridinic nitrogen signals in a single mass°spectrum° [12].APPI can extend the characterization of the petroleome°[2,°3]°to°include°non-polar°aromatic°species°and enhance the extent of molecular speciation for better understanding of petroleum processing and refining.

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Atmospheric pressure photoionization mechanisms. 2. The case of benzene and toluene

Cited by 74 publications

References 16 publications

Negative ion-atmospheric pressure photoionization: Electron capture, dissociative electron capture, proton transfer, and anion attachment

Negative ion-atmospheric pressure photoionization: Electron capture, dissociative electron capture, proton transfer, and anion attachment

Atmospheric pressure photoionization proton transfer for complex organic mixtures investigated by fourier transform ion cyclotron resonance mass spectrometry

Speciation of nitrogen containing aromatics by atmospheric pressure photoionization or electrospray ionization fourier transform ion cyclotron resonance mass spectrometry

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