Influence of the laser intensity and spot size on the desorption of molecules and ions in matrix-assisted laser desorption/ionization with a uniform beam profile |
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| Institution: | 1. Division of Internal Medicine, Baylor College of Medicine, Houston, Texas;2. Smith Center for Outcomes Research in Cardiology, Division of Cardiology, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Mass;3. Harvard Medical School, Boston, Mass;4. Duke University Medical Center, Durham, NC;5. Duke Clinical Research Institute, Durham, NC;6. Division of Cardiology, Interventional Cardiology and Endovascular Laboratory, Weill Cornell Medical College, New York-Presbyterian Hospital, New York, NY;7. Dobney Hypertension Centre, School of Medicine - Royal Perth Hospital Unit, University of Western Australia, Perth, Australia;8. Departments of Cardiology and Nephrology, Royal Perth Hospital, Western Australia, Australia;9. Neurovascular Hypertension & Kidney Disease Laboratory, Baker Heart and Diabetes Institute, Melbourne, Victoria, Australia;10. Nephrology and Dialysis Unit, Pederzoli Hospital, Peschiera del Garda Verona, Italy;11. Department of Medicine, University of Verona, Italy;12. Division of Nephrology, Department of Medicine, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, Pa;13. Cardiology Division, NYU Langone Health and NYU School of Medicine, New York, NY |
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| Abstract: | The dependence of the number of desorbed particles on laser fluence has been investigated for matrix-assisted laser desorption/ionization (MALDI) of analyte and matrix ions as well as for (photoionized) neutral matrix molecules using a homogeneous “flat-top” laser profile. Laser spot diameters ranging from 10 to 200 μm in size have been used. 2,5-Dihydroxybenzoic acid (DHB) and 3,5-dimethoxy-4-hydroxycinnamic acid (sinapic acid) have been tested as matrices. The threshold (for ion detection) is higher and the dependence of the ion signal upon higher-than-threshold fluences is stronger for directly desorbed ions than for photoionized neutral molecules. Directly desorbed analyte ions exhibit the same dependence on fluence as the matrix ions with only minor differences between the two matrices tested, so both have approximately the same detection threshold. For both ions and photoionized neutral molecules, the fluence threshold increases with decreasing spot size while the slope of the intensity/fluence curves decreases. A quasi-thermal, sublimation/desportion model was found to describe the experimental results with excellent precision. For a complete explanation, non-equilibrium effects had to be taken into account. |
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