Compound Identification Using PTR-MS

PTR-MS allows the monitoring of compounds and in some cases the identification of specific compounds in a gas. The key to doing this is mass spectrometry, and in this section we give a brief overview of mass spectra derived from PTR-MS. 

As mentioned in the previous section, the principal source of organic ions in PTR-MS is proton transfer from H3O+, as illustrated in the following reaction 

Although not always achieved, the intention in PTR-MS is to use ionization conditions where fragmentation of the protonated organic molecules is kept to a minimum, as discussed in the preceding section. In mass spectrometry parlance, the non-fragmented ion is referred to simply as the parent ion, or sometimes as the molecular ion. In the case of proton transfer, we will refer to MH+ as the protonated parent molecule. 

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