Mass Labels

While Mass Spectroscopy is not covered in our texts, other mass/density dependent technologies including X-ray Spectroscopy, Gamma Spectroscopy, & Ultrasound Analysis are covered in Guy & ffytche, An Introduction to The Principles of Medical Imaging, Imperial College Press, 2000, Chapters 4,5 & 7.

Other coverage is also found in Shung, Chapters 1, X-ray, & 2, Ultrasound, in Shung, Smith, Tsui, Principles of Medical Imaging, Academic Press, 1992.

This method uses one of several means to:

• vaporize a sample

• ionize &/or fragment it

• introduce it into a low vacuum space

• sort the fragment ions based on charge to mass ratio, m/z

• detect the ions impinging on a charge or photosensitive device, e.g., film or photodiodes

Mass Spectroscopy/Spectrometry

Note that heavy isotopes yield higher m/z for a given compound, yielding multiple MS peaks with heights proportional to the abundance of the isotopes.

A Basic Mass Spectrometer Schematic

Animations of MS (& other techniques):http://spider-dev.pharmacy.strath.ac.uk/mscpharmanal/sample.htm

http://www.chemistry.ccsu.edu/glagovich/teaching/472/ms/images/spectrometer.gif

A More Detailed Mass Spectrometer

Mass Spectrometry Bulletin:http://www.rsc.org/Publishing/CurrentAwareness/msb/index.asp

MS Basics: http://web.njit.edu/~hsieh/ene669/gc_ms.html

MS Basics in Denmark: http://130.237.33.129/klab/Kvantfysik_5A1450/var_labbar.htm

MS Basics PPTs, College of Charleston, Dept. of Chemistry:

http://www.cofc.edu/~chem/organic/Slides/MS1/index.htmhttp://www.cofc.edu/~chem/organic/Slides/MS2/index.htmhttp://www.cofc.edu/~chem/organic/ Slides/MS3/index.htm

University of Calgary MS Basics:http://www.chem.ucalgary.ca/courses/351/Carey/Ch13/ch13-ms.html

MS Basics & Theory

http://www.astbury.leeds.ac.uk/facil/MStut/mstutorial.htmhttp://www.udel.edu/chem/koh/chem333docs/MSlect1pp.pdf

http://www.files.chem.vt.edu/chem-ed/crossref/ac-mass-spec.html

MS methods differ with respect to complexity of the molecules that can be evaluated & with respect to the sensitivity of the methods. The more energy introduced in volatilizing & ionizing the sample the more likely molecules, especially large ones, will fragment. While smaller molecules may be introduced directly into the MS ionization chamber as pure compounds or as simplified mixtures resulting from the use of gas chromatographs upstream from the ionization chamber, this is not possible for most high polymers. The parent peak from the ion formed when the entire molecule looses only 1 electron provides molecular mass information. It is often vital to the analysis to find this peak which may only form under relatively “gentle” conditions.

Volatilizing & Ionizing Samples

Macromolecules may be introduced into the ionization chamber as pure materials or as simplified mixtures filtered through upstream high performance or liquid chromatographs. They may also be lifted from surfaces directly & used to examine surface compositions. The surface itself may be modified to assist volatilization & ionizatin by absorbing much of the thermal energy of the ionization source (laser, microwave, …) &/or by capturing electrons from the macromolecules to generate ions secondarily. MALDI, matrix assisted laser desorption ionization, uses easily volatilized & ionized organics such as cinnamic acid, gentisic acid, & sinapinic acid to improve movement of macromolecules such as peptides from a surface to the ion stream. Nucleic acids may be examined similarly.

Getting Polymers to Take Flight

Calibration for accuracy requires examination of molecules with known parent peak m/z & known fragmentation patterns. For more complex molecular mixtures it also requires inclusion of internal calibration molecules that provide reference peaks from which to mark m/z positions, e.g., digestive enzyme fragmentation peaks in protein digestion experiments. Note that MS methods may not have uniform sensitivity across the entire m/z range of interest; thus, multiple calibration or reference peaks may be needed. Fragmentation is also frequently run as a series of pulses each of which generate a set of data & noise peaks. Digital accumulation of pulse results accentuate true peaks & enhance sensitivity by increasing precision & specificity.

Validation Issues

Introduction to MS, Scripps:http://masspec.scripps.edu/information/index.html

More Advanced Treatments of MS

http://www.psrc.usm.edu/mauritz/maldi.html

Introduction to MALDI:

http://prospector.ucsf.edu/

Protein MS Tools:

http://winter.group.shef.ac.uk/chemputer/isotopes.html

http://www-methods.ch.cam.ac.uk/meth/ms/theory/sector.html

Double Focusing MS Schematic

http://www.york.ac.uk/depts/biol/tf/analbio_ms.htm

Applied Biosystems 4700 Proteomics Analyzer, MALDI -TOF/TOF™ tandem mass spectrometer

http://www.fastcomtec.com/

fwww/tofmas/wrecmas.htm

Example of MS/MS

Schematic

In MS/MS the initially ionized sample is passed through a 2nd ionization stage to further fragment initially formed ions yielding more structural detail.

MS vs MS/MS Analysis:http://www-helix.inrialpes.fr/article386.html

Use of MALDI-TOF 1st followed by MS/MS in proteomics:http://bmbus6.leeds.ac.uk/www/presentations/MassSpec/index.htm

http://www.ionspec.com/Applications/applications_info.htm

Proteomics & nucleic acid work often require use of MS/MS after initial MS.

www.chm.bris.ac.uk/pt/diamond/image/mwmbms.gif

Plasma Injector

www-methods.ch.cam.ac.uk/.../ theory/iontrap.html

The Ion Trap

http://www.ansto.gov.au/ansto/environment1/ams/index.html

ANTARES Accelerator Mass Spectrometer

http://www.elementalanalysis.com/icp/

ICP-MS Detection Limits

Epigenotyping using MS:http://www.epigenome.org/index.php?page=epigenotyping1

Biological Mass Spectrometry: http://www.amolf.nl/research/biological_mass_spectrometry/main.html

Archaeometry Laboratory U. of MO Research Reactor:http://www.missouri.edu/~rjse10/home.htm

Proteomics & MS: http://www.mrc-dunn.cam.ac.uk/research/proteomes.html

DNA Sequencing: http://www.cs.sunysb.edu/~skiena/648/presentations/massspec/dna.html

Pesticide Analysis: http://www.epa.gov/nerlesd1/chemistry/org-anal/reports/regmsf/regmsf.htm

BioMS at UMass:http://www.umass.edu/karbon13/index.htm

Mass SpectroscopyApplications

Analytical Microscopy: http://www.nrel.gov/measurements/analytical.html

Fragmantation patterns of organic ions:http://poohbah.cem.msu.edu/courses/CEM924JA/Fan_Shuan2/organic/index.htm

Related Topics

Crystallography: Heavy Atom Substitution:http://cns.csb.yale.edu/v1.0/tutorial/text.html

TEM Staining: http://www.lehigh.edu/~ols0/tem/staining.htmlhttp://www.aecom.yu.edu/iag/samples/files/TEM.htmlhttp://www.cimc.cornell.edu/Pages/Gallery.htmhttp://www.pegacat.com/cbetts/phd/index.html

X-ray, Ultrasound, & MRI Contrast Media

Other Mass-Dependent Methods