Mass Spectrometry 12-1 to 12-4

What does MS do?

Analysis technique that reveals:

• Molecular Weight of a pure compound

• Molecular Formula (High Resolution MS)

• Some structural information

• “Chemical Fingerprint” that can be matched to a known compound.

Advantages

+ Very very small sample size

+ Can be coupled with Gas Chromatography

+ Complementary to UV/vis, IR, NMR

+ Versatile: many techniques have been

developed, from small organics to proteins and DNA.

+ Data base friendly

Disadvantages

- Destructive to sample

- Limited structural information

- Too sensitive – background noise a problem

- Expensive & Sophisticated instrument

http://www.epa.gov/ada/about/pics/gc_lc_ms.jpg

Take that, you foul machine!http://www.underthepier.com/images/16_smashing-fruits.jpg

Applications

•Detect and identify the use of steroids in athletes

•Monitor the breath of patients by anesthesiologists during surgery

•Determine the composition of molecular species found in space

•Determine whether honey is adulterated with corn syrup

•Locate oil deposits by measuring petroleum precursors in rock

•Monitor fermentation processes for the biotechnology industry

•Detect dioxins in contaminated fish

•Determine gene damage from environmental causes •Establish the elemental composition of semiconductor materials

http://www.asms.org/whatisms/p1.html

How does MS work?

• Electron Impact Ionization if most popular fragmentation technique

• A stream of high energy electrons are directed towards organic molecules

• The electrons fragment the molecules in rational and repeatable ways

• Positive ions that are produced are separated by their mass to charge ratio

Gas Chromatography and Mass Spectrometry (GC-MS): A match made in analytical chemistry heaven

Detailed Fragmentation of Methane

H C

H

H

H

Methane 16 g/mole

+ e H C

H

H

H

Methane radical cation 16 m/z

+ 2e

H C

H

H

H = H C

H

H

H

H C

H

H

H H C

H

H

+ H

15 m/z

Fragmenation

Billiards Analogy?

http://www.albany.edu/news/photo_archive/albums/reslife/images/billiards.jpg

Piniata?

http://www.roystory.com/images/Jimmy%5F5/pages/piniata_jimmy2.html

Spectra and Data Table for the Electron Ionization of Methane

High Resolution MS can determine molecular formula

Isotope Atomic Mass (amu) 12C 12.000000 1H 1.007825 16O 15.994914 14N 14.003050

M.W. = 44

C3H8 3(12) + 8(1.007825) = 44.0626

N2O 2(14.003050) + 15.994914 = 44.001014

C2H4O 2(12) + 4(1.007825) + 15.994914 = 44.026214

CO2 12 + 2(15.994914) = 43.989828

Some atoms reveal their presence by isotope patterns

79Br

H2C

CH281Br

H2C

CH2

MW = 107MW = 109

79Br

H2C

CH2

H2C

CH381Br

H2C

CH2

H2C

CH3

MW = 136 MW = 138

MW = 57

H2C

CH2

H2C

CH3

Fragmentation of Alkanes

http://www.lobos.nih.gov/cbs/img/alkane.jpg

MS fragmentation of pentaneH3C

H2C

H2C

H2C CH3 + e H3C

H2C

H2C

H2C CH3 + 2e

m/z = 72

H3CH2C

H2C

H2C CH3

H3CH2C

H2C

H2C CH3

H3CH2C

H2C CH2 CH3

m/z = 57

H3CH2C CH2 H2C CH3

H3CH2C CH2 H2C CH3

m/z = 29

m/z = 43

MS fragmentation of pentaneH3C

H2C

H2C

H2C CH3 + e H3C

H2C

H2C

H2C CH3 + 2e

m/z = 72

H3CH2C

H2C

H2C CH3

H3CH2C

H2C

H2C CH3

H3CH2C

H2C CH2 CH3

m/z = 57

H3CH2C CH2 H2C CH3

H3CH2C CH2 H2C CH3

m/z = 29

m/z = 43

Dimethylpentane

hexane

Alkyl fragments. general formula: CnH2n+1

m/z formula structure(s)

15 CH3

C2H5

C3H7

C4H9

C5H11

C6H13

C7H15

29

43

57

71

86

99

CH3

H3C

HC

CH3 H2C

H2C

CH3

H3CC

CH3

CH3

H2C

H2C

CH2

CH3 H3C

HC

CH2

CH3

H3CCH

CH3

CH2

H3CCH2

Fragmentation of molecules with oxygen and/or nitrogen

http://www.chemistry.unimelb.edu.au/staff/chutton/research/Image15.gif

H3CH2C

H2C

H2C OH + e

+ 2e

m/z = 74

H3CH2C

H2C

H2C OH

Unshared Electrons on “O” and “N” usually get knocked off first

H3CH2C

H2C CH OH

H

H3CH2C

H2C

HC OH + H

m/z = 73

Fragmentation occurs in a chemically rational and predictable way

H3CH2C

H2C

H2C OH + e

+ 2e

m/z = 74

H3CH2C

H2C

H2C OH

H3CH2C

H2C

H2C OH

H3C

H2C CH2 H2C OH

m/z = 31

H3CH2C

H2C CH OH

H

H3CH2C

H2C

HC OH + H

m/z = 73

H3CH2C CH

H2C OH

H

H3CH2C

HC CH2 + H2O

m/z = 56

However, Fragment abundance is difficult to predict

H3CH2C

H2C

H2C OH + e

+ 2e

m/z = 74

H3CH2C

H2C

H2C OH

H3CH2C

H2C CH OH

H

H3CH2C

H2C

HC OH + H

m/z = 73

H3CH2C

H2C

H2C OH

H3C

H2C CH2 H2C OH

m/z = 31

H3CH2C CH

H2C OH

H

H3CH2C

HC CH2 + H2O

m/z = 56

Favored Fragmentation Pathway

Gas ChromatographyMass Spectrometry

GC

GC

MS

MS Molecular Structure

C

CH

C

HC

HC

C

O

CH3

HO

H2C

CH2

C

O

CH3

C11H14O3

M.W. 194

C

CH

C

HC

HC

C

O

CH3

HO

H2C

C9H11O2

M.W. 151

CH2

C

CH

C

HC

HC

C

O

CH3

HO

CH2

C8H9O2

M.W. 137C

CH

C

HC

HC

C

C6H3O

M.W. 91O

MS fragmentation of 2-pentanone

H3C C

O

H2C

H2C CH3 C

O

CH3

H2CH2C CH3

m/z = 43

H3C C

O

H2C

H2C CH3

CH3

O CH2C

H2C CH3

m/z = 71

H3C C

O

H2C

H2C CH3

+ eH3C C

O

H2C

H2C CH3

+ 2e

m/z = 86

H3C

C

O

CH2

CH2

CH2

H

McLafferty

H3C

C

OH

CH2

CH2

CH2

m/z = 58

m/z = 43

m/z = 87

m/z = 71m/z = 58

MS fragmentation of 2-pentanone

H3C C

O

H2C

H2C CH3 C

O

CH3

H2CH2C CH3

m/z = 43

H3C C

O

H2C

H2C CH3

CH3

O CH2C

H2C CH3

m/z = 71

H3C C

O

H2C

H2C CH3

+ eH3C C

O

H2C

H2C CH3

+ 2e

m/z = 86

H3C

C

O

CH2

CH2

CH2

H

McLafferty

H3C

C

OH

CH2

CH2

CH2

m/z = 58

Time-of-Flight Instrumentshttp://www.uibk.ac.at/ionen-angewandte-physik/umwelt/research/pics/animation.gif