Ion/Molecule Reactions

When performing ion/molecule reactions within the final electrode the ion beam exiting the electrode structure was precisely aligned with the inlet of the MS. Once this alignment condition was established it was observed that the signal recorded by the mass spectrometer was largely independent of the position of the nanoESI spray tip within Esource. This was realized by repositioning the spray tip with the 3 axis moving stage while recording MS spectra. Other than cases in which the spray tip was removed from Esource or moved to within 1-2 mm of the electrode walls, MS spectra and intensities remained unchanged. This effect has potential utility in decoupling spray position from recorded intensities to improve reproducibility when changing spray tips.

Mass spectra of the ion/molecule reactions between protonated cyclohexylamine and tert-butylamine ions with DMMP vapor as sampled from the final region of the polymeric electrode assembly are shown in Fig. 3.7. Similar IMRs using analogs of DMMP have previously been demonstrated for the identification of amino functionalities in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer [28]. These reactions highlight the potential usefulness of ion manipulation outside the mass spectrometer in exploring ion/molecule reactions for functional group identification. The ability to perform and interrogate these reactions outside the MS may allow for a condition in which an ion separation is performed at atmospheric pressure after a reaction has taken place to identify the presence of a target compound in the analyte mixture.

Mass spectra showing reaction of protonated cyclohexylamine with DMMP vapor (a) and tert-butylamine with DMMP vapor (b)

Fig. 3.7 Mass spectra showing reaction of protonated cyclohexylamine with DMMP vapor (a) and tert-butylamine with DMMP vapor (b)

 
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