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

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 M.W. = 44 C3H8  3(12) + 8(1.007825) = 44.0626 C2H4O  2(12) + 4(1.007825) + 15.994914 = 44.026214 N2O  2(14.003050) + 15.994914 = 44.001014 CO2  12 + 2(15.994914) = 43.989828

Some atoms reveal their presence by isotope patterns

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

MS fragmentation of pentane

MS fragmentation of pentane

Dimethylpentane

hexane

Fragmentation of molecules with oxygen and/or nitrogen http://www.chemistry.unimelb.edu.au/staff/chutton/research/Image15.gif

Unshared Electrons on “O” and “N” usually get knocked off first Fragmentation occurs in a chemically rational and predictable way

However, Fragment abundance is difficult to predict

Gas Chromatography Mass Spectrometry GC GC MS

MS  Molecular Structure

MS fragmentation of 2-pentanone

m/z = 43 m/z = 87 m/z = 71 m/z = 58

MS fragmentation of 2-pentanone

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