The width of the distribution is strongly decreased with CHCA as matrix, meaning that most probably fragmentation of part of the protein-cluster has occurred. already observed for bare proteins). However, the ion intensity obtained in negative mode are much lower than those reported for positive mode. Concerning processes for ionizing analytes with both ion polarity in MALDI, it was suggested that two matrix molecules were involved in the MALDI process and may yield a pair of protonated and deprotonated matrix ions that produce analyte molecules in protonation or deprotonation states. Energy transfer process was also suggested, where following laser irradiation a nearby excited matrix molecule can transfer its energy to the analyte dimer through a short range energy transfer mechanism and trigger disproportionation, which leads to one protonated and one deprotonated analyte being produced simultaneously. Proteins may have numerous acidic sites and may readily be deprotonated (see Table ).