Advances in flow reactor techniques for the study of gas‐phase ion chemistry

Graul, Susan T.; Squires, Robert R.

doi:10.1002/mas.1280070302

Cited by 185 publications

(82 citation statements)

References 435 publications

(29 reference statements)

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“…The flowing afterglow [12] is a versatile reaction vessel commonly used as an ion source in mass spectrometry. However, recognizing that flow reactors are not limited to ionic systems [12, 24 -26], we reasoned that neutralneutral reactions in the flowing afterglow could be used to generate gaseous samples of reagents generally too corrosive or hazardous to be handled using standard techniques.…”

Section: Resultsmentioning

confidence: 99%

“…All experiments were carried out in a flowing afterglow triple quadrupole mass spectrometer that has been previously described [12,13]. Fluoride was prepared by 70 eV electron ionization of neutral fluorine gas (5% in He, Spectra Gases Inc., Branchburg, NJ) and carried by helium buffer gas (0.400 torr, flow (He) ϭ 190 STP cm 3 /s) through the flow tube where it was allowed to react with neutral reagent vapors, either added through micrometering valves or generated by neutral-neutral reactions.…”

Section: Methodsmentioning

confidence: 99%

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In situ generation of HCN for mass spectrometric studies

Chacko

Krouse

Hammad

et al. 2006

J. Am. Soc. Mass Spectrom.

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Hydrogen cyanide (HCN) for use in ion preparation can be generated in the gas phase by the neutral-neutral reaction of trimethylsilyl cyanide (Me 3 SiCN) and water in a flowing afterglow mass spectrometer. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions such as F Ϫ (HCN), Cl Ϫ (HCN), CN Ϫ (HCN), PhNO 2 ·Ϫ (HCN), Me 3 SiO Ϫ (HCN),and PhSiF 4 Ϫ (HCN), many of which are otherwise difficult to generate. The bond dissociation energy of CN Ϫ (HCN), generated by using this approach, has been measured by using energy-resolved collision-induced issociation (CID) to be 0. [2,3] in both the condensed phase and the gas phase. Whereas solvated halide [4,5] and alkoxide [6] ions are readily examined, clusters of cyanide are especially of interest because CN Ϫ is a pseudohalide with an ambidentate nature. Moreover, the conjugate acid, HCN, is a weak acid (⌬H acid ϭ 350.9 Ϯ 0.2 kcal/mol) [7] with extensive positive charge character on the hydrogen, making it an attractive hydrogen-bonding moiety in the gas phase [8]. Recently, HCN has gained much interest as it has been found to be a tracer for young stellar objects, and it has been detected in the atmosphere of Titan [9].An important challenge in carrying out studies involving cyanide or hydrogen cyanide is in the safe generation of the reagents. Because of its toxicity, HCN is rarely used directly as a reagent gas. Previous studies by Larson and McMahon [8] and Meot-Ner and coworkers [10] have used the solution phase reaction of KCN and acids (HCl or H 2 SO 4 ) to produce HCN, which was directly added to the mass spectrometer. Subsequently, ion-exchange equilibria [8] and van't Hoff measurements [10] were used to determine anion-neutral binding energies of CN Ϫ and HCN containing clusters. Recent studies have utilized the reaction of CH 4 and NH 3 with Pt catalyst to generate HCN in a molecular beam apparatus [11].In this work, we describe a simple in situ approach for generation of HCN for ion clustering studies. Hydrogen cyanide is formed by the neutral-neutral reaction of trimethylsilyl cyanide, Me 3 SiCN, with water in a flowing afterglow reactor. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions and report energy-resolved CID studies of the HC 2 N 2 Ϫ ion formed. From these CID studies, we report a direct measurement of the [CN-HCN] Ϫ bond dissociation energy. Throughout this paper, HC 2 N 2 Ϫ refers to the m/z 53 species that has been observed and characterized. However, this notation does not indicate a specific ion structure. The structures of the HC 2 N 2 Ϫ isomers are addressed computationally at the end of this study. ExperimentalAll experiments were carried out in a flowing afterglow triple quadrupole mass spectrometer that has been previously described [12,13]. Fluoride was prepared by 70 eV electron ionization of neutral fluorine gas (5% in He, Spectra Gases Inc., Branchburg, NJ) and carried by helium buffer gas (0.400 torr, flow (He) ϭ 190 STP cm 3 /s) through the flow tube wh...

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

In situ generation of HCN for mass spectrometric studies

Chacko

Krouse

Hammad

et al. 2006

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

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“…14 The technique is well developed and has been thoroughly described in the literature. Two reviews are particularly noteworthy, one by Ferguson et al 15 that describes the principles and mathematics involved and one by Graul and Squires 16 that describes the developmental history of the technique. Here we will concentrate on the aspects of the technique pertinent to making measurements at high temperature.…”

Section: Methodsmentioning

confidence: 99%

Flowing afterglow apparatus for the study of ion–molecule reactions at high temperatures

Hierl

Friedman

Miller

et al. 1996

Review of Scientific Instruments

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We describe two versions of a high temperature flowing afterglow apparatus. With a stainless steel flow tube wrapped with heating tape we have obtained data over the range 300-1300 K. In a version with a ceramic flow tube in a commercial furnace we have obtained data over the range 300-1600 K. The ceramic version is designed to take data up to 1800 K, but we have encountered experimental problems at the upper temperature range. The design modifications to a standard flowing afterglow needed to make measurements at elevated temperatures are described in detail, as are problems associated with operating at elevated temperatures. Samples of data are given.

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“…All gas-phase ion/molecule reactions were carried out using a flowing afterglow-triple quadrupole mass spectrometer that has been described previously [56,57]. Fluoride was prepared by 70 eV electron ionization of neutral fluorine gas (5% in He, Spectra Gases Inc., Branchburg, NJ) and carried by helium buffer gas (0.400 Torr, flow(He) ϭ 190 STP cm 3 /s) through the flow tube, where it was allowed to react with vapors from silanes added through micrometering valves.…”

Section: Instrumental Description and Data Analysismentioning

confidence: 99%

Fluorotrimethylsilane affinities of anionic nucleophiles: A study of fluoride-induced desilylation

Krouse

Wenthold

2005

J. Am. Soc. Mass Spectrom.

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In this study, preparation and decomposition of five novel pentavalent fluorosiliconates, RSi(CH 3 ) 3 F Ϫ (R ϭ CH 3 CH 2 O, CF 3 CH 2 O, (CH 3 ) 2 CHO, (CH 3 ) 3 SiO, and (CH 3 ) 3 SiNH) is used to investigate the process of fluoride-induced desilylation. The siliconates were characterized by collision-induced dissociation and energy-resolved mass spectrometry. Decomposition of RSi(CH 3 ) 3 F Ϫ leads to loss of the nucleophile R Ϫ and FSi(CH 3 ) 3 , except in the case of (CH 3 ) 3 SiNHSi(CH 3 ) 3 F Ϫ , where HF loss is also observed. Ion affinities for FSi(CH 3 ) 3 have been measured for all five nucleophiles, and compare well with computational predictions. The observed trend of the bond dissociation energies resembles the trend of ⌬H acid values for the corresponding conjugate acids, RH. Additionally, this data has been incorporated with existing thermochemistry to derive fluoride affinities for four of the silanes (R ϭ CH 3 CH 2 O, (CH 3 ) 2 CHO, (CH 3 ) 3 SiO, and (CH 3 ) 3 SiNH). We use the fluoride affinity of the silanes and the FSi(CH 3 ) 3 affinity of the departing nucleophilic anion to assess the feasibility of fluorideinduced desilylation of the silanes examined in this work. (J Am Soc Mass Spectrom 2005, 16, 697-707)

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Advances in flow reactor techniques for the study of gas‐phase ion chemistry

Cited by 185 publications

References 435 publications

In situ generation of HCN for mass spectrometric studies

In situ generation of HCN for mass spectrometric studies

Flowing afterglow apparatus for the study of ion–molecule reactions at high temperatures

Fluorotrimethylsilane affinities of anionic nucleophiles: A study of fluoride-induced desilylation

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