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Surface modification and laser pulse length effects on internal energy transfer in DIOS
Guanghong Luo1, Yong Chen, Gary Siuzdak
1Department of Chemistry, Institute for Proteomics Technology and Applications, George Washington University, Washington, DC 20052, USA.
The Journal of Physical Chemistry. B
|December 27, 2005
Summary
Benzyl-substituted benzylpyridinium chloride salts probed internal energy transfer in desorption/ionization on porous silicon (DIOS). Surface modifications and laser pulse durations influenced ion production and energy distributions, offering insights into desorption dynamics.
Area of Science:
- Analytical Chemistry
- Surface Science
- Mass Spectrometry
Background:
- Desorption/ionization on porous silicon (DIOS) is a soft ionization technique.
- Understanding internal energy (IE) transfer is crucial for optimizing ionization efficiency and minimizing analyte fragmentation.
- Modifying surface properties can influence analyte-surface interactions and desorption characteristics.
Purpose of the Study:
- To investigate internal energy (IE) transfer during desorption/ionization on porous silicon (DIOS) using benzyl-substituted benzylpyridinium (BP) chloride salts as thermometer ions.
- To evaluate the effect of surface derivatization (TMS, NH2, PFA, PFP) on IE transfer and ion production thresholds.
- To compare DIOS with matrix-assisted laser desorption/ionization (MALDI) in terms of IE transfer and plume expansion dynamics.
Main Methods:
- Utilized benzyl-substituted benzylpyridinium (BP) chloride salts as thermometer ions.
- Modified porous silicon surfaces via silylation to create TMS, NH2, PFA, and PFP derivatized surfaces.
- Employed two laser sources: a 4 ns nitrogen laser and a 22 ps mode-locked 3 x omega Nd:YAG laser.
- Measured survival yields and extracted internal energy distributions at various laser fluences.
Main Results:
- Increasing laser fluence generally did not alter IE transfer for DIOS, contrasting with MALDI.
- Surface derivatization minimally impacted survival yields but affected ion production thresholds.
- DIOS consistently yielded lower mean IE values and narrower IE distributions (ps laser) compared to MALDI.
- IE distribution width for DIOS with ns laser excitation varied with surface modification.
Conclusions:
- DIOS exhibits distinct desorption/ionization characteristics compared to MALDI, attributed to plume expansion dimensionality.
- Surface modifications primarily influence the threshold for ion production rather than IE transfer.
- The choice of laser pulse duration significantly affects IE distribution width in DIOS.
- DIOS offers a promising alternative for soft ionization with controllable energy transfer.