Introduction to Mass Spectroscopy

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Presentation Transcript

Mass Spectroscopy (MS) : 

Mass Spectroscopy (MS) Determine the relative amounts and masses of: Isotopes Fragments of large molecules Sample is propelled by electrical & magnetic fields Particles separated on the basis of particle mass Peak height indicates relative amount Usually used in conjunction with another instrumental method (FTIR or GC)

Mass Spec for IsotopesChlorine : 

Mass Spec for IsotopesChlorine What do we know? Chlorine is diatomic Chlorine has 2 isotopes Chlorine-35 (~75% abundance) Chlorine-37 (~25% abundance) How many peaks would we get if we tested chlorine? Which peaks would be strongest? 5 35 (atomic Cl) 70 (molecular Cl)

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A B C D E

Identity of Peaks in Chlorine’s Mass Spectrum : 

Identity of Peaks in Chlorine’s Mass Spectrum A B C D E Monatomic chlorine (35Cl) Monatomic chlorine (37Cl) Molecular (diatomic) chlorine (35Cl- 35Cl) Molecular (diatomic) chlorine (35Cl- 37Cl) Molecular (diatomic) chlorine (37Cl- 37Cl)

Interpreting Mass Spectra for Compounds : 

Interpreting Mass Spectra for Compounds Like a jigsaw puzzle (what fragments/ions could have this mass?) Highest mass peak with highest intensity is probably the non-fragmented molecule (most common isotopes) Both fragments of a “split” should be present Fragmentation commonly occurs at: Branched carbon atoms

Mass Spectrum of Methylpropane : 

Mass Spectrum of Methylpropane A B C

Identity of Peaks in Methylpropane’s Mass Spectrum : 

Identity of Peaks in Methylpropane’s Mass Spectrum A B C Methyl propane Propyl fragment Methyl fragment

Interpreting Mass Spectra for Compounds : 

Interpreting Mass Spectra for Compounds Like a jigsaw puzzle (what fragments/ions could have this mass?) Highest mass peak with highest intensity is probably the non-fragmented molecule (most common isotopes) Both fragments of a “split” should be present Fragmentation commonly occurs at: Branched carbon atoms Carbonyl groups

Mass Spectrum of Acetone : 

Mass Spectrum of Acetone A B C

Identity of Peaks in Acetone’s Mass Spectrum : 

Identity of Peaks in Acetone’s Mass Spectrum A B C Acetone Carbonyl-methyl fragment Methyl fragment

Interpreting Mass Spectra for Compounds : 

Interpreting Mass Spectra for Compounds Like a jigsaw puzzle (what fragments/ions could have this mass?) Highest mass peak with highest intensity is probably the non-fragmented molecule (most common isotopes) Both fragments of a “split” should be present Fragmentation commonly occurs at: Branched carbon atoms Carbonyl groups Look for “characteristic” differences in the peaks Difference of 35  Probably chlorine Difference of 19  Probably fluorine

Mass Spectrum of Chloromethane : 

Mass Spectrum of Chloromethane Difference of 35, which is characteristic of a chlorine atom

Interpreting Mass Spectra for Compounds : 

Interpreting Mass Spectra for Compounds Like a jigsaw puzzle (what fragments/ions could have this mass?) Highest mass peak with highest intensity is probably the non-fragmented molecule (most common isotopes) Both fragments of a “split” should be present Fragmentation commonly occurs at: Branched carbon atoms Carbonyl groups Look for “characteristic” differences in the peaks Difference of 35  Probably chlorine Difference of 19  Probably fluorine If you know possible structure, look for fragments that might match peaks that appear