Mass spec

[sam0001]

Does fragmentation occur in the ionisation chamber or due to the magnetic field?

Basically, the question I'm struggling with, is ate any given moment, what is present in the ionisation chamber?

[Mao]

Fragmentation generally occurs in the ionisation chamber.

Mass spec instrumentation can be quite complex, but for fragmentation studies the design isn't too complex. Typically, you inject your sample into the sample port, and there is a 'nebuliser' which turns it into gas. Then, an electron source shoots semi-low energy electrons to bombard your gaseous sample. The key here is the electrons have enough energy to break bonds, but not enough to knock out core electrons and cause some high energy reaction. Anyhow, the molecules break after being bombarded by electrons, then flies down the magnetic field.

Note that only a very small portion of the sample gets ionised, due to low collision frequencies and low energy collisions. From memory, the ionisation efficiency is somewhere in the range of . However, the detector is sensitive enough to deal with these small quantities.