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Mass Spectrometry. Courtesy www.lab-initio.com. Purpose of Mass Spectrometry. P roduces spectra of masses from the molecules in a sample of material, and fragments of the molecules. U sed to determine the elemental composition of a sample the masses of particles and of  molecules

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Mass spectrometry

Mass Spectrometry

Courtesy www.lab-initio.com


Purpose of mass spectrometry
Purpose of Mass Spectrometry

  • Producesspectra of masses from the molecules in a sample of material, and fragments of the molecules.

  • Used to determine

    • the elemental composition of a sample

    • the masses of particles and of molecules

    • potential chemical structures of molecules by analyzing the fragments

    • the identity of unknown compounds by determining mass and matching to known spectra

    • the isotopic composition of elements in a molecule


Stages
Stages

The ionizer converts some of the sample into ions.

Mass analyzers separate the ions according to their mass-to-charge ratio.

The detector records either the charge induced or the current produced when an ion passes by or hits a surface


Mass spectrometry methods
Mass Spectrometry Methods

http://www.chem.arizona.edu/massspec/intro_html/intro.html


Mass spectrum of co 2
Mass Spectrum of CO2

Molecular ion peak

[CO2]+ = 44

Fragment Peaks

[C]+ = 12

[O]+ = 16

[CO]+ = 28


Mass spectrum of bromine br 2
Mass Spectrum of Bromine, Br2

Bromine has two isotopes: 50.69% 79Br and 49.31% 81Br

Molecular Ion Peaks

[79Br81Br]+

[79Br79Br]+

Fragments

[81Br81Br]+

79Br+

81Br+



Answers methyl bromide ch 3 br
Answers: Methyl Bromide, CH3Br

[CH381Br]+

[CH81Br]+and[CH379Br]+

[CH281Br]+

[C81Br]+and [CH279Br]+

[CH3]+

[CH79Br]+

[81Br]+

[C79Br]+

[79Br]+


Practice methylene chloride ch 2 cl 2
Practice: Methylene Chloride (CH2Cl2)

Chlorine is 75.77% 35Cl and 24.23% 37Cl


Practice vinyl chloride ch 2 chcl
Practice: Vinyl Chloride (CH2CHCl)

Chlorine is 75.77% 35Cl and 24.23% 37Cl


Spectra of larger molecules
Spectra of Larger Molecules

Spectra of large molecules have many fragments, and the interpretation of their spectra is beyond the scope of this course.

Codeine, C18H21NO3


Toluene c 7 h 8 fragmentation
Toluene (C7H8) Fragmentation

**Note that the molecular ion peak is NOT the dominant peak in the spectrum


Mass spectrometry in forensics
Mass Spectrometry in Forensics

  • Mass spectrometry is used to confirm the identify of unknowns, such as illegal drugs

  • Unknowns are often not pure, and must be separated from a mixture

  • Gas chromatography is used to separate the components of the mixture

  • Mass spectrometry “fingerprints” the components, so that they can be matched to existing known spectra

Gas

Chromatograph

Mass

Spectrometer

Mixture


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