Abstract

The utility of CF3+ as a chemical-ionisation reagent for the identification of volatile organic compounds (VOCs) is explored. CF3+ and CF2H+, produced from the discharge of CF4, have been used as chemical ionization (CI) precursor ions with a representative functional mixture of VOCs in Chemical Ionisation Reaction Mass Spectrometry (CIR-MS), a multi-reagent analogue of PTR-MS.Reacting CF3+ with a functionally varied range of VOCs, under 100Td and 120Td accelerating electric fields (E/N), produced markedly different fragmentation patterns. Whereas hydride ion transfer was found to be the main reaction mechanism with n-alkanes. CF3+ acts as a Lewis acid, a strong electrophile with aromatics and nitriles. In VOCs with carbonyl groups, CF3+ forms an intermediate complex leading to the substitution of oxygen by fluorine. Target VOCs with longer alkyl chains in general show greater fragmentation, starting at C5 and becoming progressively more significant by C7.A brief comparison is made with the comparable H3O+ reactivity. From the comparison between CF3+ and H3O+, it is clear that CF3+ is a “more aggressive” reagent ion but offers utility in terms of distinctive mass shifts with certain functional groups.

Highlights

  • Proton Transfer Reaction Mass Spectrometry (PTR-MS) has seen widespread uptake for the measurement of volatile organic compounds (VOCs) in a wide range of application areas.[1]

  • There is a strong analogy in the work in CIR-TOF-MS and PTR + SRI-MS to the capabilities of SIFT-MS8 which can switch between different reagent ions

  • We demonstrated the effectiveness of CF3+ and CF2H+ derived from CF4 as chemical ionisation reagents for the quantification of n-alkanes in CIR-TOF-MS.[9]

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Summary

Introduction

Proton Transfer Reaction Mass Spectrometry (PTR-MS) has seen widespread uptake for the measurement of volatile organic compounds (VOCs) in a wide range of application areas.[1]. The proton transfer reactions produce mainly RH2 ions, characteristic of protonation, along with a similar large background of smaller intensity fragments (Tables 2a and 3a).

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Conclusion

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