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 phasemass spectrometry is our most valuable analytical tool for determining accurate molecular massesalso can give information about structureproteins can now be sequenced by MSMS-MS-3Mass Spectrometry (MS)Mass Spectrometry (MS)MS-MS-4A Mass SpectrometerA Mass SpectrometerA mass spectrometer is designed to do three thingsconvert neutral atoms or molecules into a beam of positive (or negative) ionsseparate the ions on the basis of their mass-to-charge (m/z) ratiomeasure the relative abundance of each ionMS-MS-5A Mass SpectrometerA Mass SpectrometerElectron Ionization MSin the ionization chamber, the sample is bombarded with a beam of high-energy electronscollisions 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 IonMolecular ion (M):Molecular ion (M):a radical cation formed by removal of a single electron from a parent molecule in a mass spectrometerFor 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 witha plus sign to show that it is a cationa dot to show that it has an odd number of electronsMS-MS-7Molecular IonMolecular Ionat 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 SpectrumMass spectrum:Mass spectrum:a plot of the relative abundance of ions versus their mass-to-charge ratioBase peak:Base peak:the most abundant peakassigned an arbitrary intensity of 100The relative abundance of all other ions is reported as a % of abundance of the base peakMS-MS-9MS of dopamineMS of dopaminea partial MS of dopamine showing all peaks with intensity equal to or greater than 0.5% of base peakMS-MS-1010Other MS techniquesOther MS techniquesWhat we have described is called electron ionization mass spectrometry (EI-MS)Other MS techniques includefast atom bombardment (FAB)matrix-assisted laser desorption ionization (MALDI)chemical ionization (CI)electrospray ionization (ESI) MS-MS-1111ResolutionResolutionResolution:Resolution:a measure of how well a mass spectrometer separates ions of different masslow resolution:low resolution:refers to instruments capable of separating only ions that differ in nominal mass; that...
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Chapt12_MS - MS-MS-1Mass SpectrometryMass...

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