Fast atom bombardment-mass spectrometry background ions

In FAB, the sample is usually dispersed in a non-volatile liquid matrix, such as glycerol or diethanolamine, and deposited at the end of a sample probe that can be inserted into the ion source. The sample on the probe is ionised when bombarded by the fast atom beam. However, ionisation of the matrix also occurs, leading to a very large background signal. The technique is thus limited for the analysis of small molecules. Fast-moving ions (Cs+ or Ar+) can be used instead of fast-moving atoms, which is the basis of a technique called liquid secondary ion mass spectrometry (LSIMS). 

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