In the Electron Impact MS the organic compound is introduced in theion source (under high vacuum) and bombarded with an high energyelectron beam (70 eV)organiccompoundElectron beame(70 eV)GasMChromatographIon source chamberPressure=10-5-10-7torranodeM + e-M+ + 2 e'the collision of electron beam transfer to the organic compound alarge energy content thereby releasing one electron and producing apositively charged radicalIREEA-NanjingAgricultural University/April2008
In the Electron Impact MS the organic compound is introduced in the ion source (under high vacuum) and bombarded with an high energy electron beam (70 eV) M Gas Chromatograph Electron beam (70 eV) Ion source chamber Pressure = 10-5-10-7 torr e- e- e e - - anode M + e- M + + 2 eorganic compound the collision of electron beam transfer to the organic compound a large energy content thereby releasing one electron and producing a positively charged radical IREEA-Nanjing Agricultural University/ April 2008
the positive charged radical is highly unstable and it startimmediately to loss the excess of energy by breaking down(fragmentation) in small positively charged fragments with lowermasses (positive mass fragments) of smaller molecular weightmtm+mtmtmmtmtfragmentationmtM+mtmtmtmtmtmtthe various mass fragment (ions) are then collected by electroniclens and accelerating slit and pushed in the mass analyzer whichprovides a separation with respect to their molecular weightthe various fragments are then collected by sampling at regularinterval (usually1 second)and forwardedtothedetector systemMass spectraIREEA-NanjingAgriculturalUniversity/April2008
the positive charged radical is highly unstable and it start immediately to loss the excess of energy by breaking down (fragmentation) in small positively charged fragments with lower masses (positive mass fragments) of smaller molecular weight the various mass fragment (ions) are then collected by electronic lens and accelerating slit and pushed in the mass analyzer which provides a separation with respect to their molecular weight m + m + m + m + m m + + m + m + m + m + m + m + m + m + the various fragments are then collected by sampling at regular interval (usually 1 second) and forwarded to the detector system M + fragmentation Mass spectra IREEA-Nanjing Agricultural University/ April 2008
Ion sourceElectronic lens andIsabpeaccelerating slitSadPawFunstacceshtEhectronFOOSSeccndcceta5OnbeaEGCMsecdiaPepedFeeacceterntirgonmlansnotinregiontacyonbeante.seOTiwmocopeMass analyzerMagpetic fechiougentireanernblyCoilectae AssamblyCollector and+Okons inamplifiergisteAnasturtTengefCoaecNemowsitoDo?IREEA-NanjingAgricultural University/April 2008
Ion source Electronic lens and accelerating slit Mass analyzer Collector and amplifier IREEA-Nanjing Agricultural University/ April 2008
Example of mass spectra:linear hydrocarbon /alkaneHentriacontane C3,H64 m.w. 436the smaller masses arethe higher masses areenrgetically stable and henceenergeticallyunstableandand have a short lifetimeare more abundantMass spectram# 82757100Mass fragments43718550M+12799,13436、25228130933 3373513653793931411691972242中业计608040100120140160180200220240260280300320340360380400420440IREEA-NanjingAgriculturalUniversity/April2008
Example of mass spectra: linear hydrocarbon /alkane Hentriacontane C31 H64 m.w. 436 Mass spectra 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 0 50 100 43 57 71 85 99113127 141 169 197 224 252 281 30933 337351365379393 436 M + Mass fragments m+ 57 m + m+ 127 85 the smaller masses are enrgetically stable and hence are more abundant the higher masses are energetically unstable and and have a short lifetime IREEA-Nanjing Agricultural University/ April 2008
the main advantage of EI-MS is that each compound classeshavethesamefragmentationpatternthe mass spectra are fingerprint of specific organic compounds classesIREEA-NanjingAgriculturalUniversity/April2008
the main advantage of EI-MS is that each compound classes have the same fragmentation pattern the mass spectra are fingerprint of specific organic compounds classes IREEA-Nanjing Agricultural University/ April 2008