09 MS 2 - Mass spectroscopy(continued Ionization methods Electron impact(ionization Chemical ionization Desorption ionization(MALDI Spray

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1 Mass spectroscopy (continued) Ionization methods 1. Electron impact (ionization) 2. Chemical ionization 3. Desorption ionization (MALDI) 4. Spray ionization (ESI) Electron Impact (Ionization) • Good for mw< 1000 Da • Good for less polar molecules • 70 eV or greater to cause ionization but 10 eV will break bonds (1 eV 96.49 kJ/mol): M (vapor) + e - M + . + 2 e - Significant fragmentation can occur and the M + . may be missing.
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2 Chemical Ionization • A more controllable method of ionization than EI • The molecule (analyte) reacts with an ion that was generated by EI at high pressure. Various types of molecular ions may be formed: M + Ar + . M + . + Ar Charge transfer M + CH 5 + (M+H) + + CH 4 Proton transfer M + OH - (M-H) - + H 2 O Proton abstraction Reagent gases for proton transfers (+/-)
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3 Example: phenyl propyl ketone • Isobutane (PA=802 kJ/mol) • Methane (PA=544 kJ/mol) • Phenyl propyl ketone (~870 kJ/mol) Non-proton reactions: charge exchange The reagent ion is a radical cation (hard and soft)
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This note was uploaded on 10/08/2009 for the course CHEM 439 taught by Professor Falzone,c during the Spring '08 term at Pennsylvania State University, University Park.

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09 MS 2 - Mass spectroscopy(continued Ionization methods Electron impact(ionization Chemical ionization Desorption ionization(MALDI Spray

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