Chapt12_MS

Chapt12_MS - MS-MS-1Mass SpectrometryMass...

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Unformatted text preview: MS-MS-1Mass SpectrometryMass SpectrometryChapter 12MS-MS-2Mass Spectrometry (MS)Mass Spectrometry (MS)◆An analytical technique for measuring the mass-to-charge ratio (m/z) of ions in the gas phase•mass spectrometry is our most valuable analytical tool for determining accurate molecular masses•also can give information about structure•proteins can now be sequenced by MSMS-MS-3Mass Spectrometry (MS)Mass Spectrometry (MS)MS-MS-4A Mass SpectrometerA Mass Spectrometer◆A mass spectrometer is designed to do three things•convert neutral atoms or molecules into a beam of positive (or negative) ions•separate the ions on the basis of their mass-to-charge (m/z) ratio•measure the relative abundance of each ionMS-MS-5A Mass SpectrometerA Mass Spectrometer◆Electron Ionization MS•in the ionization chamber, the sample is bombarded with a beam of high-energy electrons•collisions between these electrons and the sample result in loss of electrons from sample molecules and formation of positive ions+++CHHHHCHHHe-2e-HMolecular ion(a radical cation)MS-MS-6Molecular IonMolecular Ion◆Molecular ion (M):Molecular ion (M):a radical cation formed by removal of a single electron from a parent molecule in a mass spectrometer◆For our purposes, it does not matter which electron is lost; radical cation character is delocalized throughout the molecule; therefore, we write the molecular formula of the parent molecule in brackets with•a plus sign to show that it is a cation•a dot to show that it has an odd number of electronsMS-MS-7Molecular IonMolecular Ion•at times, however, we find it useful to depict the radical cation at a certain position in order to better understand its reactionsCH3CH2OCH(CH3)2CH3CH2OCH(CH3)2..MS-MS-8Mass SpectrumMass Spectrum◆Mass spectrum:Mass spectrum:a plot of the relative abundance of ions versus their mass-to-charge ratio◆Base peak:Base peak:the most abundant peak•assigned an arbitrary intensity of 100◆The relative abundance of all other ions is reported as a % of abundance of the base peakMS-MS-9MS of dopamineMS of dopamine•a partial MS of dopamine showing all peaks with intensity equal to or greater than 0.5% of base peakMS-MS-1010Other MS techniquesOther MS techniques◆What we have described is called electron ionization mass spectrometry (EI-MS)◆Other MS techniques include•fast atom bombardment (FAB)•matrix-assisted laser desorption ionization (MALDI)•chemical ionization (CI)•electrospray ionization (ESI) MS-MS-1111ResolutionResolution◆Resolution:Resolution:a measure of how well a mass spectrometer separates ions of different mass•low resolution:low resolution:refers to instruments capable of separating only ions that differ in nominal mass; that...
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This note was uploaded on 09/19/2011 for the course CHM 262 taught by Professor Staff during the Spring '08 term at Purdue.

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Chapt12_MS - MS-MS-1Mass SpectrometryMass...

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