Reactions at the interface between source and analyser

Atmospheric pressure sources need to have a device for the desolvation of the ions, such as a heated capillary, a heated gas curtain, collisions at intermediate pressure in a focusing multipole. The increase in internal energy induces the dissociation of the associated ion-molecules. Furthermore, the ions are at low pressure and thus the probability of the reverse reaction is strongly decreased. For example, if a molecule forms a complex with an 

This reaction occurs even if M is less basic than ammonia. So, the protonated molecular ion of a sugar may be formed by desolvatation of its ammoniacal complex. 

In negative ion mode, the acetate ion is used and acetic acid can be evacuated by pumping to obtain the deprotonated molecular ion of the analyte  

Bentley, T.W. and Johnstone, R.A.W. (1970) Mechanism and structure in mass spectrometry a comparison with other chemical processes, in Advances in Physical Organic Chemistry, vol. 8 (ed. V. Gold), Academic Press, London. 

Harrison, A.G. (1983) Chemical Ionisation Mass Spectrometry, CRC Press, Boca Raton, FL. 

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