Reactive Tandem Ion Mobility Spectrometry with Electric Field Fragmentation of Alcohols at Ambient Pressure

Abstract

A tandem ion mobility spectrometer at ambient pressure with a reactive stage produced fragment ions by water elimination from protonated monomers of alcohols with carbon numbers three to nine. Protonated monomers of individual alcohols were mobility isolated in a first drift region and were fragmented to carbocations at 64 to 128 Td and 45 to 89°C. Precursor and fragment ions were mobility characterized in a second drift region. Enthalpies for fragmentation of ROH2 + to primary carbocations were calculated as 76 to 97 kJ/mol and enthalpies for subsequent charge migration to 2° carbocations were −49 to −58 kJ/mol. Plots of drift times for pairs of protonated monomer and fragment ions from alcohols, esters, alkanes, and aldehydes produced distinctive trend lines attributed to fragmentation paths characteristic of chemical class. Specific combinations of drift times for fragments and precursor ions provide additional chemical information for spectral interpretation in ion mobility spectrometry.

Field Induced Fragmentation (Fif) Spectra of Oxygen Containing Volatile Organic Compounds with Reactive Stage Tandem Ion Mobility Spectrometry and Functional Group Classification by Neural Network Analysis

“…In contrast, IMS spectra obtained at ambient pressure usually contain one or two product ion peaks, often protonated monomers and/or proton bound dimers. While peaks for fragment ions are not routinely observed in mobility spectra, the decomposition of ions at elevated temperatures has been described for butyl acetates and lately for nitro-esters of explosives. − Ions at ambient pressure can also undergo fragmentation in electric fields >100 Td (or ∼14 000 V/cm) as demonstrated in differential mobility spectrometry with ions of aromatic compounds, acetates, organophosphorous compounds, and alcohols. , Recently, fragments of ions were generated in tandem mobility analyzers from precursor ions that were mobility isolated in a first mobility drift tube, fragmented using a reactive (middle) stage of electric fields , or thermal fragmenters, , and mobility analyzed in a second drift tube. Fragment ions derived from these three steps, if specific to a chemical class or functional group, could introduce structural information into mobility spectra and enable molecular identification.…”

“…Some spectral detail could arise also from thermal decomposition, though little progress was made further in exploring the significance of structure information in spectra in the absence of mass analysis of ions. Other concerns included limitations in the resolving power of small drift tubes and inadequate technology to control fragmentation reactions, now possible with wire grid assemblies. , …”

“…The benefits of reactive stage tandem IMS methods are found in the chemical simplicity in fragmenting only a specific ion and in spectral clarity where fragment ions appear on a baseline free of ions from matrix or analyte with other drift times. In a preliminary study of alcohols from propanol to nonanol with this concept, hydrates of protonated monomers of alcohols were dehydrated through the loss of water adducts and finally fragmented to a carbocation . Unlike proton transfer reaction mass spectrometry (PTR-MS) with several successive fragmentations to even smaller mass fragments with increased E / N or multiple fragments with high kinetic energy IMS at 19 Torr, only a single fragment ion was observed in the FIF spectra with a variable E / N up to 129 Td for ion fragmentation .…”

Mechanism of atmospheric pressure chemical ionization of morphine, codeine, and thebaine in corona discharge–ion mobility spectrometry: Protonation, ammonium attachment, and carbocation formation

“…However, the energy difference between the N‐ and O‐protomers is large; hence, the relative abundance of the O‐protomers is too small to be observed in the IMS spectra. Therefore, the observed peaks for morphine (M1 & M2) and codeine (C1 & C2) are not due to protonation of these compounds at different sites (N and O); instead, one peak is due to protonation and formation of the N‐protomers, and another peak is attributed to carbocation formation upon water elimination from the protonated molecules 44 …”

High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS) at 40 mbar

“…Another important benefit of HiKE-IMS is the possibility of changing the reduced electric field strength in the drift region independently of the reduced electric field in the reaction region in order to separate substances by their field-dependent ion mobility as known from FAIMS and DMS ,− allowing for improved substance identification. Furthermore, high reduced electric field strength can lead to fragmentation, ,, also improving substance identification.…”