Competing ion decomposition channels in matrix-assisted laser desorption ionization
Guanghong Luo1, Ioan Marginean, Louise Ye
1Department of Chemistry, The George Washington University, Washington, D.C. 20052, USA.
The Journal of Physical Chemistry. B
|May 21, 2008
Summary
Matrix-assisted laser desorption ionization (MALDI) internal energy transfer was studied using the benzyltriphenylphosphonium (BTP) thermometer ion. Picosecond lasers show lower energy transfer than nanosecond lasers, impacting ion fragmentation pathways.
Area of Science:
- Analytical Chemistry
- Mass Spectrometry
- Physical Chemistry
Background:
- Matrix-assisted laser desorption ionization (MALDI) is a key technique for analyzing biomolecules.
- Understanding internal energy transfer in MALDI is crucial for controlling ion fragmentation.
- The benzyltriphenylphosphonium (BTP) ion serves as a thermometer to probe energy deposition.
Purpose of the Study:
- To compare internal energy transfer in MALDI using nanosecond and picosecond lasers.
- To investigate the influence of different MALDI matrices (CHCA, SA, DHB) on ion fragmentation.
- To elucidate the mechanisms governing ion formation based on laser excitation and matrix properties.
Main Methods:
- Utilized the benzyltriphenylphosphonium (BTP) thermometer ion to quantify internal energy.
- Employed both nanosecond (4 ns) and picosecond (22 ps) laser excitation.
- Analyzed fragmentation patterns (F1: tropylium ions, F2: triphenylphosphine ions) and branching ratios (I F1/I F2) in CHCA, SA, and DHB matrices.
Main Results:
- Picosecond laser excitation resulted in lower internal energy transfer compared to nanosecond excitation across all matrices.
- The branching ratio (I F1/I F2) showed a moderate preference for tropylium ion formation (1 < I F1/I F2 < 6) in SA and DHB, and CHCA at low fluences.
- At higher fluences, CHCA exhibited a dramatic shift towards tropylium ion production (I F1/I F2 ≈ 30) with both laser types, correlating with increased BTP internal energies.
Conclusions:
- The mechanism of desorption differs between nanosecond (phase explosion) and picosecond (stress-confinement) lasers.
- CHCA matrix, particularly at higher fluences, facilitates greater internal energy deposition, leading to enhanced fragmentation compared to SA and DHB.
- The findings provide insights into optimizing MALDI conditions for controlled ion fragmentation and analysis.
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