Mass Spectrometry Flashcards
What is MS?
Separation of ions by mass to charge ratio
Also the production of ions that are subsequently separated of filtered according to their mass to charge (m/z) ration and detected
Where does the molecular ion peak occur?
Molecular ion mass + 1
Advantage of MS
- Provides MW info and structure info
- Very low limits of detection
- Minute amount of sample required (1 nanogram is all you need)
- Fast
- Can be used for a wide variety of possible sample
_______ requires much lower amount of sample than NMR
Mass Spectrometry
Difference between mass spectrometry and mass spectroscopy
Mass Spectrometry: based on particle
Mass Spectroscopy: based on frequency
Applications of Mass Spectrometry
- Structural determination of organics, biomolecules, polymers, catalysts etc
- Mixture Analysis
- Elemental Analysis
- Quality Control
- Environmental Monitoring
What is the most common type of mass spectrometry?
Electron Ionisation
What is the process of electron ionisation?
- Volatile sample is vaporised
- The sample is blasted with electrons and excess energy is absorbed (M+)
- Uni-molecular decomposition of M+
- Produce ions
- a- mass analysis of all ions
b- data recording
c- plot of bar graph - mass spectrum
What is M+?
Molecular ion
What is a mass spectrum?
It’s a relative abundance of ions of different m/z produced in an ion souce
What is the purpose of operating mass spectrometers at low pressures
- Minimise ion/molecule collisions
2. Prevent from high voltage discharges
Disadvantages of rough (vacuum) pump
- The gas to be exhausted outside the lab
- Time consuming: as it requires to heat/cool oil for hours
Disadvantages of diffusion pump
- Expensive
- The machine requires a constant flow of water
- Doesn’t do well with power outages (Causes oil to become carbon)
Advantages of Diffusion Pump
- Cheaper as they’re an older machines
-
- Method of ionisation
- Electron ionisation
- Introduce sample as a gass/vapourise to a gass
- Ionise through interaction with 70eV electron beam
- Can accept sample from a GC
- Method of ionisation
- Chemical ionisation
- Chemical ionisation: a progression from EI
- Accept samples from GC