9. MS Techniques Flashcards
What is IR-MS?
Isotope Ratio Mass Spectrometry
What is GC-MS?
Gas Chromatography Mass Spectrometry
What is LC-MS?
Liquid Chromatography Mass Spectrometry
What does EI mean?
Electron Impact Ionization.
This is where analyte molecules are directly ionized through collision with a bombarding electron stream
-> removal of an electron to form a radical cation species.
What do we do in mass spectrometry?
We determine the mass-to-charge ratio of ions formed from molecules and fragments of these.
What are the steps in MS?
- Formation of ions
- Separation of ions according to their mass to charge ratio, m/z
- Measuring ion current or counting ions
- Data processing
What is MALDI?
Matrix Assisted Laser Desorption Ionisation
What API?
Atmospheric Pressure Ionization
What is APCI?
Atmospheric Pressure Chemical Ionization
What are some LC-MS solvents?
Water, acetonitrile, methanol, ethanol, propanol isopropanol.
What are some acceptable additives for LC-MS?
Acetic acid, formic acid, ammonium hydroxide, ammonium format, ammonium acetate
The ratio between C-12 and C-13 (i.e. in plants) is…?
not constant. It depends on photosynthesis.
What are the steps in GC-MS?
Typically they include:
- Sample components separation
- Ionization of sample components
- Separation and detection of gas-phase ions
What does the mass spectrometer do?
It separates gas phase ions according to their mass to charge ratio (m/z) value.
Most common ionization methods in GC-MS?
Electron impact ionization (EI) and chemical ionization (CI).
What advantages are there to GC-MS (in comparison to LC-MS)?
- higher chromatographic resolution
- higher peak capacity
- single mobile phase
- fewer issues (solubility and separation)
What is CI?
Chemical ionization.
This is where analyte molecules are charged through reaction processes with a charged reagent gas plasma producing either anion or cation species depending upon the analyte and analyzer polarity.
What is make-up gas?
Make up” gas is a gas flow that is used to sweep components through a detector to minimize band broadening
What are the disadvantages of EI?
It is a relatively harsh form of ionization
-> parent molecule often breaks apart.
How can MS-MS analysis be achieved?
Choose one:
- By coupling multiple analyzers (of the same or different kind)
- With an ion trap and carrying out successive fragmentations of trapped ions.
What are some applications for GC-MS?
- Inorganic chemistry analysis (inorg. compounds with low mol. weight)
- Environmental sciences (analysis of a wide range of contaminants of low mol. weight)
- Food analysis (analysis of molecules of importance in the food industry)
- Pharmacochemistry (drug activity)
- Bioanalysis (quantification/identification of metabolites in biological fluids)
- Polymers (structure from behaviour at elevated temperatures)
