MS Flashcards
(22 cards)
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
Proteomics
Pharmaceutics
Environmental
Proteomics
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
Astrochemistry
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
