Desorption Ionization Doping with Alkali Metal Salts

3 Desorption Ionization Doping with Alkali Metal Salts 

In desorption ionization methods, like field desorption [11], fast-atom bombardment [12], and matrix-assisted laser desorption (MALDI) [13], adding small amoimts of alkali metal salts to the sample on the emission wire (in field desorption) or target (in fast-atom bombardment and MALDI) may result in the observation of adduct ions [M + Alkali] (see also Sect. 7.2). This is generally termed doping with alkali metal salts. In principle, when a platimrm or tungsten wine, to be used in thermoionic emission, is doped with alkali metal salts, gas-phase alkali metal ions may be produced as well. It may be questioned whether this is due to a thermoionic or desorption/ionization effect. 

A typical example of this type of doping is a fragmentation stutfy of the flavo-noid glycoside ratin, adducted with different alkah metal ions (LL, Na% or K+), by post-soirrce decay MALDI time-of-flight (TOF) MS [14]. Differences in fragment ions and especially the relative abimdance of fragment ions were observed (see Sect. 7.5.2). Nitmerous other examples of this type of studies are available. 

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