Processes of Ion Formation in MALDI

In case of UV light-absorbing analytes, direct photoionization can also occur. The ftequently observed positive and negative radical ions M [61,62] and M [63-65] can only be generated by removal or capture of an electron. Thus, M and 

M ions point towards the occurrence of photoionization [61], charge exchange, and electron capture in the gas phase [42,61]. Which of the above processes contributes most to ion formation depends on the actual combination of matrix, analyte, and possibly present additives or contaminants. 

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