Photoionization Mass Spectroscopy

Isomeric Resolution

Figure 4

Isomeric resolution enables researchers to discriminate between different isomers in reactants or determine the isomer profiled in reaction products. In some cases, novel isomeric species can be detected by photoionization that are difficult to measure by other means. One prominent example is formaldehyde oxide, the simplest example of a Criegee intermediate, critical steps in the ozonolysis of alkenes that had never been directly seen in the gas phase before its detection in dimethyl sulfoxide (DMSO) oxidation by CRF researchers in collaboration with atmospheric chemists from University of Bristol and University of Manchester. In these experiments, measured with the sector instrument, the CH2OO isomer was separated spectroscopically from the substantial CH2S side product, which has very nearly the same mass (see Figure 4).

By using an orthogonal acceleration mass spectrometer in their experiment, however, the mass resolution is just sufficient to resolve these species in mass:

Figure 5: Orthogonal acceleration mass spectrometer