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Flashcards in MS Deck (22)
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Electric current

flow of negative electrons


Electromagnetic field

field of force
-electric and magnetic components
-definite amount of electromagnetic energy


Production of an electromagnetic field can result from? can be generated by?

Result from motion of electric charge (wire)

Generated by a flow of positively charged ions (mass spectrometer)


What would happen if a current carrying wire is placed in external magnetic field?

jump as it is deflected when the 2 magnetic fields interact


Mass spectrometry

Powerful analytical tool
-provides info on both molecular mass and molecular structure
-1000x more sensitive than other analytical techniques such as IR or NMR spectroscopy


How MS works/process? General steps

Victor Is A Daft Duck

1) Vaporization
2) Ionization
3) Acceleration
4) Deflection
5) Detection


MS: Vaporization

-positively charged ions are:
1)produced w/an associated magnetic field
2) deflected in a controlled external magnetic field
-atom/molecules of the substance must be free to move
-SAMPLE must be VAPorized if not a gas


MS: Ionization

-bombard the sample with high energy electrons from an electron gun
-electron is knocked off producing a positive ion (Cation)
-sometimes produces:
1) double charged ions
2)molecules to be broken into different fragments
3) radical (dot)


MS: Acceleration

Positive ions are accelerated by an electric field
-focused into a fine beam
-passing through a series of slits with increasing negative potential
-ions must be able to move freely through the apparatus without colliding with air molecules
-system removes air to create a vacuum


MS: Deflection

-The beam of fast-moving positive ions is DEFLECTED by a strong external magnetic field


What 2 factors does deflection depend on?

Mass (m) of the ion
-less mass=more deflection

Charge (z) of the ion
-ions with 2+ charge deflected more than 1+
more positive charge=more deflection

Combined into m/z ratio
small m/z=large deflection


MS: Detection

Ions are detected electronically
-positive ions arrive at detector and pick up electrons to become neutral
-movement of electrons is detected, amplified, and recorded
-external magnetic field in deflection can be ajdusted
-ions with different m/z ratios can be detected
-printout of intensity vs m/z ratio is produced


As the molecule gets bigger...

possibility of fragmentation increases
-Mass spectra become more complex


Final decisions about structure are made after combining evidence from mass spec with other analytical tools such as:

-Infrared (IR) spectroscopy
-Ultraviolet-visible (UV-VIS) spectroscopy
-Nuclear magnetic resonance (NMR) spectroscopy


Liquid Chromatography- Mass spectrometry

Allows complex mixtures to be separated by liquid chromatography using small capillary columns
-Most modern
1) allows use of very small quantities of samples
2) Important since MS destroys the sample

As the separated substances leave the column they are automatically fed into a mass spectrometer
-each component can be identified


Some applications of LC-MS




study of proteins including digestion products


Gas Chromatography-Mass Spectrometry

Growing in popularity due to:
-compact nature of the equipment
-speed of use (less than 90secs)
-relatively low cost

Combines a chromatography step to separate out components
-uses an inert gas as the mobile phase


Some applications of GC-MS

Airport security
Fire forensics


High Resolution-Mass spectrometry

Can distinguish compounds with the same nominal mass but different actual mass caused by different elemental composition


Some applications of HR-MS

analyzing interactions between drugs and body tissues


Common Fragmentations

When a molecule is split during fragmentation
-pieces formed tend to be more stable types
-Height of the detected peaks provide an indication of stablity