Mass Spectrometry (Chapter 20): Based on ionization of gas phase molecule followed by analysis of the masses of the ions produced The Mass Spectrum: Graph of ion intensity versus mass-to-charge ratio (m/z)(units daltons,Da) Fig 20-1 91 100 Base peak 80 Mw=106 60H 106 Molecular 40 ion peak YCH2CH, 20 04 0 102030405060708090100110 m/ molecular ion peak (M+)m/z corresponds to MW of singly- charged molecule fragment peak m/z less than MW of singly-charged molecule base peak most intense m/z CEM 333 page 18.1
Mass Spectrometry (Chapter 20): Based on ionization of gas phase molecule followed by analysis of the masses of the ions produced The Mass Spectrum: Graph of ion intensity versus mass-to-charge ratio (m/z) (units daltons, Da) Fig 20-1 molecular ion peak (M+) m/z corresponds to MW of singlycharged molecule fragment peak m/z less than MW of singly-charged molecule base peak most intense m/z CEM 333 page 18.1
Instrument Components: 10-510-81 Readout Fig20-10 sample introduction system-vaporize sample ion source -ionizes analyte gas molecules mass analyzer-separates ions according to m/z detector counts ions vacuum system-reduces collisions between ions and gas molecules CEM 333 page 18.2
Instrument Components: Fig 20-10 • sample introduction system - vaporize sample • ion source - ionizes analyte gas molecules • mass analyzer - separates ions according to m/z • detector - counts ions • vacuum system - reduces collisions between ions and gas molecules CEM 333 page 18.2
Ion sources: TABLE 20-1 Ion Sources for Molecular Mass Spectrometry Basic Type Name and Acronym lonizing Agent Gas phase Electron impact(ED) Energetic electrons Chemical ionization(CI Reagent gaseous ions Field ionization(Fl） High-potentialelectrode Desorption Field desorption (FD) High-potentiaeeoe Electrospray ionization(ESI) High electrical field Matrix-assisted desorption/ionization (MALDI) Laser beam Plasma desorption(PD) Fission fragments from252Cf Fast atom bombardment(FAB) Energetic atomic beam Secondary ion mass spectrometry(SIMS) Energetic beam of ions Thermospray ionization(TS) High temperature CEM333 page 18.3
Ion sources: CEM 333 page 18.3
Hard ion sources leave excess energy in molecule-extensive fragmentation Soft ion sources little excess energy in molecule-reduced fragmentation Fig 20-2 CH:(CH2)sCH2OH Hard Ionization 112 20 120 T140 160 141 CHj(CH2)gCH2OH (M-OH)* Soft CHCH,CH时 69 Ionization (M) 84 100 140 160 6 CEM 333 page 18.4
Hard ion sources leave excess energy in molecule - extensive fragmentation Soft ion sources little excess energy in molecule - reduced fragmentation Fig 20-2 CEM 333 page 18.4
Gas Phase Ion Sources: (A)Electron Impact (ED)Ion Source: Electron bombardment of gas/vapor molecules M+e(~70eV)→Mt+2e (about 10%ionized) Fig 20-3 Shield Heater Electron slit Pirst acce Molecular Filamen I slit leak 三( To mass analyzer Repelle onizing region Electron lon accelerating beam Anode Electron energy ~70 eV 1eV=1.6x10-19Cx1V (1V=1J.C-1 =1.6x10-19J =96.486 kJ.moli-1 CEM 333 page 18.5
Gas Phase Ion Sources: (A) Electron Impact (EI) Ion Source: Electron bombardment of gas/vapor molecules M + e - (~ 70 eV) ® M+ + 2e- (about 10-4 % ionized) Fig 20-3 Electron energy ~70 eV 1eV º1.6x10-19 C´1V (1V = 1 J×C -1 ) =1.6x10-19 J = 96.486 kJ×mol-1 CEM 333 page 18.5