Agriculture Reference
In-Depth Information
Figure 2.3.
MALDI ion source and ionization process. The matrix-analyte crystal impacted by laser beam
excites the matrix, which in turn ionizes the analyte. Analyte ions are collected, analyzed, and detected by
the mass spectrometer.
proposed by Ehring et al., the absorbed energy migrates into the matrix molecules and
focuses on the
event [62]. The matrix ions are formed as a result of the
interactions between electrons excited to singlet and higher states. The secondary
matrix
“
pooling
”
analyte reactions yielding analyte ions comprise proton transfer, electron
transfer, and gas-phase cationization through interactions with alkali metals [63].
MALDI is a soft ionization technique, with mass spectra that are typically characterized
by either [M
-
H]
ions. Depending on the
properties of the matrix and analytes, as well as some other experimental conditions
(e.g., matrix/analyte ratio, crystallization conditions, or sample deposition method),
multiply charged species can also be formed [64].
H]
+
and alkali metal adducts or [M
+
2.3.1.2 Optimization of Key Parameters
In order to achieve the desired outcome of MALDI-MS analysis, a number of factors
have to be considered. The most important parameters to be optimized are the
following:
Type of matrix.
Isolation of target analytes and sample cleanup.
