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Analytical Chemistry 2.2 > Mass Spectrometry > Flashcards

Mass Spectrometry Flashcards

1
Q

What is MS?

A

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

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2
Q

Where does the molecular ion peak occur?

A

Molecular ion mass + 1

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3
Q

Advantage of MS

A
  • 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
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4
Q

_______ requires much lower amount of sample than NMR

A

Mass Spectrometry

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5
Q

Difference between mass spectrometry and mass spectroscopy

A

Mass Spectrometry: based on particle

Mass Spectroscopy: based on frequency

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6
Q

Applications of Mass Spectrometry

A
  • Structural determination of organics, biomolecules, polymers, catalysts etc
  • Mixture Analysis
  • Elemental Analysis
  • Quality Control
  • Environmental Monitoring
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7
Q

What is the most common type of mass spectrometry?

A

Electron Ionisation

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8
Q

What is the process of electron ionisation?

A
  1. Volatile sample is vaporised
  2. The sample is blasted with electrons and excess energy is absorbed (M+)
  3. Uni-molecular decomposition of M+
  4. Produce ions
  5. a- mass analysis of all ions
    b- data recording
    c- plot of bar graph
  6. mass spectrum
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9
Q

What is M+?

A

Molecular ion

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10
Q

What is a mass spectrum?

A

It’s a relative abundance of ions of different m/z produced in an ion souce

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11
Q

What is the purpose of operating mass spectrometers at low pressures

A
  1. Minimise ion/molecule collisions

2. Prevent from high voltage discharges

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12
Q

Disadvantages of rough (vacuum) pump

A
  • The gas to be exhausted outside the lab

- Time consuming: as it requires to heat/cool oil for hours

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13
Q

Disadvantages of diffusion pump

A
  • Expensive
  • The machine requires a constant flow of water
  • Doesn’t do well with power outages (Causes oil to become carbon)
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14
Q

Advantages of Diffusion Pump

A
  • Cheaper as they’re an older machines

-

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15
Q
  1. Method of ionisation

- Electron ionisation

A
  • Introduce sample as a gass/vapourise to a gass
  • Ionise through interaction with 70eV electron beam
  • Can accept sample from a GC
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16
Q
  1. Method of ionisation

- Chemical ionisation

A
  • Chemical ionisation: a progression from EI

- Accept samples from GC

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17
Q
  1. Method of ionisation

Atmospheric Pressure Ionisation (API)

A
  • Spray liquid into the ion source and use hot gas to remove the solvent molecules
  • A voltage gradient will cause ions to be pulled into the mass analyser
  • Can accept sample from an LC
18
Q
  1. Method ionisation

Matrix-assisted laser desorption/ionisation (MALDI)

A
  • put sample on a metal plate and cover with a matrix compound
  • place inside ion source and focus a laser beam onto the surface
  • ions will created and pulled into the mass analyser
  • Mostly performed on built time of flight instruments
19
Q

Whats the typical speed of diffusion pump?

A

Diffusion pump has typical speeds between 500-800 L/sec

20
Q

What’s the pressure of diffusion pump?

A

It has pressure of 10^-9 to 10^-10 Torr but with pump oil background

21
Q

What’s turbomolecular pump

A

A clean vacuum pump that’s suitable as the main pump of a mass spectrometer.

22
Q

What is a turbomolecular pump used for?

A

Used in a wide range of high and ultra-high vacuum applications, covering both clean application.

23
Q

Disadvantages of turbomolecular pump

A
  • Expensive to repair

- Random solids can damage the blades

24
Q

Advantages of turbomolecular pump

A
  • Cheap to operate
  • Dependable
  • Require no re-generation
  • Operate at high pumping speeds in the high and ultra high vacuum range
25
Q

Cyropump

A
  • Gases are frozen (condensed) on surfaces cooled to 10-20K with liquid nitrogen
  • Works well with gasses that freeze
  • Gasses that don’t freeze are absorbed w/activated charcoal traps in the condenser
  • Used in conjunction with turbopumps
26
Q

Disadvantages of Cryopumps

A
  • It has to stay cold

- Nitrogen pump can not be emptied

27
Q

Define volatile

A

A sample can go into the gas phase and remain stable

28
Q

Define direct introduction

A

Sample that is place directly into the ion source region of the mass spectrometer

29
Q

Direct introduction for gases and volatile liquids

A
  1. Syringe, leak valve/pulse valve introduction of sample into a reservoir
  2. Volatile liquids have to be vaporised - through pumping them alone/heating the inlet system
30
Q

Define Hyphenated-MS technique

A

Sample goes from a chromatograph, IR / ICP through an interface and into the MS source

31
Q

Electrostatic focusing

A

Ions are moved and focus by placing voltages on metal components (plates, tubes, etc)

Positive voltages repel positive ions - attract negative ions n vice versa

The higher the voltage, the faster ions are accelerated away from or towards the voltage

Can repel ions by using the same charge

32
Q

Define “Steering beams” of electron ionisation

A

Beams of varying voltages that can be applied to move the ions up, down, left or right

33
Q

Uses of electrostatic

A
  • Photocopies
  • Laser printer
  • Ink jet printer
  • Electrostatic air filters
34
Q

What does electrostatic focusing can do

A
  • Extract ions out the ionisation source
  • Form a focused ion beam that goes into the mass analyser
  • Accelerate ion into the mass analyser
35
Q

Define electron volt

A

The energy acquired by a singly charged particle in moving across a potential difference of 1 volt

36
Q

What is the first ionisation potential

A

Measures of the energy that is required to remove one valence electron from a neutral atom and is an atomic property which reflects the outermost electronic configuration

37
Q

What happen if the electron energy is lower than the ionisation potential?

A

The ions wont be made

38
Q

If the electron energy is too high, it will cause what problem with ions?

A

The number of ions made and the current plateau off because there is so much energy - can break any bond.

39
Q

Why would large electron energies such as 70eV be used in routine analysis?

A
  • At high energies, the ionisation process is saturated (all molecules come into contact with the electron beam and ionise)
  • Small changes in energy have negligible effects on the spectra
40
Q

Advantages of EI

A
  • Good sensitivity
  • Can do + and - ions but negative ion sensitivity is low for most compounds
  • Can withstand pressures to about 10^-5 - too high could result to burning the filament
  • Works with high resolution and MS/MS experiments

Analytical Chemistry 2.2 (3 decks)

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