a) How is a mass spectrum defined?
A mass spectrum is the two-dimensional representation of signal intensity (ordinate) versus m/z (abscissa). The intensity of a peak, as signals are usually called, directly reflects the abundance of ionic species of that respective m/z ratio which have been created from the analyte within the ion source.
b) Assign the following terms to the EI mass spectrum below: base peak, molecular ion peak, and fragment ion peak.
c) Can you identify the unknown compound from its spectrum?
Fragment ion peaks at m/z 12 and 16 point towards atomic ions of 12 and 16 u, i.e., 12C+. and 16O+. ions. The ion at m/z 28 corresponds to [M-16]+, and therefore indicates [M-O]+. Thus, the molecular ion seems to consist of C and O exclusively. The mass difference between M+. and m/z 16 is 28 u and should result from loss of a molecule of CO. Other neutral losses are not observed.
This spectrum belongs to carbon dioxide, CO2, 44 u.
The ion at m/z 22 is not a fragment ion, but is due to the doubly charged molecular ion, CO22+.