Question

. In general what are the differences between hard ionization and soft ionization sources? What kind of

   molecular spectra would you expect to see from using each technique? Provide one example for

   each.

Answer 1

Ionization refers to the production ions suitable for resolution in the mass analyser.

1) Hard ionization techniques involves a processes which impart high quantities of residual energy in the analysing molecule - this results in large degrees of fragmentation which means there is rupturing of the bonds which are in general labile in nature. Resultant ions tend to have m/z lower than the molecular mass. In most cases the molecular ion peak is either very small in intensity and thus lost in the Signal to noise of teh mass spectrum.

The most common example of hard ionization is electron ionization (EI).

2) Soft ionization technique involves a processes which impart little residual energy to the analysing molecule, which in turn result in little fragmentation. Thus the actual molecular ion peak remain predominant.

Examples include electrospray ionization (ESI), and matrix-assisted laser desorption/ionization (MALDI).