An Investigation into the Mechanism of MALDI－. The Correlation between Cation Formation and Anion FormationI. The Effect of Free Electrons on Anion Formation
Date Issued
2008
Date
2008
Author(s)
Liu, Bo-Hong
Abstract
Matrix assisted laser desorption ionization (MALDI) is a soft mass spectrometry ion source. Since invented in the 1980’s, it has been wildly used in various fields. However, its mechanism remains quite unclear. This mechanistic study is done with Dual-polarity time-of-flight mass spectrometer (DTOFMS), which can simultaneously detect both polarities of ions produced in MALDI.In the first part of this work, the variation of anion to cation ratio is monitored in crystallized and decrystallized sample. The variation of the two samples are obviously different. There are two conclusions in this part: (1) crystallization condition of the sample has an influence to the formation of both polarities of the matrix molecular ions. (2) The formation pathways of two polarities of matrix molecular ions are lowly correlated.In the second part of this work, I monitored the laser fluence dependency of the intensity of matrix molecular cation and anion. It was observed that matrix molecular anion formation has lower energy threshold. This observation is consistent with the conclusion in the first part, i.e. the formation pathways of two polarities of matrix molecular ions are lowly correlated. Next I adopt a piece of glass, which is an insulator, as a sample support. It was observed that the energy threshold of matrix molecular anion is no longer lower than that of cation. Therefore it can be conclude that matrix molecular anion may form by direct capture of photoelectron in plume.
Subjects
mass spectrometer
matrix assisted laser desorption ionization
MALDI
dual-polarity mass spectrometry
Type
thesis
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