MS2- instrument design and components

Question 1

Which phase should the sample be in when reaching the MS interior?

Answer 1

The sample should be in gas phase, because the interior of the MS is in high vacuum.

Question 2

what is MS often used in combination with during sample introduction?

Answer 2

• Direct injection (infusion of liquid samples)
• Solid support (assisted solid to gas transition)
• Chromatographic interfase (analyte separation)

Question 3

What is the point of chromatography?

Answer 3

• Separation of complex mixtures of analytes. Fx. Blood samples.
• To introduce an additional dimension to your analysis: time- resolution (retention time)
• Reduce complexity og sample analysis at any time-point
• Improve sensitivty to your analysis by being able to measure different concentration at once.

Question 4

In column chromatography what will be the first compound to reach the bottom? The one with weak or strong interaction?

Answer 4

The one with weaker interaction.

Question 5

What is the phenomenon eddy diffusion in chromatography?

Answer 5

Molecules takes different paths through the column and causes peaks to get broader.

Question 6

What is the phenomenon Logitudinal diffusion in chromatography?

Answer 6

Molecules spread along the longitudinal axis (diffusion over time).

Question 7

What is the phenomenon mass transfer/convection in chromatography?

Answer 7

Delay of equlibrium between phases and causes bad separation at a fast flow.

Question 8

What is the Van Deemter equation?

Answer 8

H=A+B/u+C∗u

Question 9

What happens in the Van Deemter plot of plate height H when the velosity is increased ?

Answer 9

• The eddy diffusion is unchanged
• The longitudinal diffusion decreases
• The resistance to mass transport increases
  And the plate hight first decrease an then increase creating a minimum showing the optimal separation.

Question 10

What is a TIC?

Answer 10

It stands for total ion count and plots the intensity of all ions that are recorded at any given time and the sum of all ions at any time point.

Question 11

What is a EIC/XIC?

Answer 11

It stands for extracted ion chromatogram and its signal is obtained from a spcific m/z value

Question 12

What is a BPC?

Answer 12

It is a way of plotting MS where the intensity of the most intense ion at any time point is given as y

Question 13

Name the most important mass analyzers named during the lectures.

Answer 13

• TOF (time of flight)
• Q (linear quadrupole)
• LIT (linear quadrupole ion trap)
  -Orbitrap

Question 14

What are the 4 problematics with ion behavior in linear TOF mode??

Answer 14

• Different starting times
  ○ Ions are not all generated at exactly the same moment.
• Different starting locations
  ○ Ions originate from slightly different locations in the ion source.
• Different initial kinetic energies
  ○ Even ions with the same m/z may have varied velocities due to energy spread.
• Different initial directions of motion
  Ions do not all travel perfectly straight toward the detector.

Question 15

How can the problematics from linear mode in TOF be solved?

Answer 15

• Through reflector mode, where particles are “smooth out” before returing from the reflector. The downside of this method is that it creates more noice in the spectra.
• A reflectron is an electrostatic mirror (a series of charged plates) that ions enter and are reflected back toward the detector. It corrects for differences in kinetic energy between ions of the same mass-to-charge ratio (m/z).

Question 16

What is post-source decay (PSD)?

Answer 16

A fragmentation process in TOF-MS where ions, after being accelerated, break apart due to internal energy.

Question 17

What is a quadrupole?

Answer 17

A quadrupole in MS is a type of mass analyzer, which is a device that selects ions based on their mass-to-charge ratio (m/z) using electric fields. It consisist of four parallel metal rods whith are paired 2-2 where two rods have a +DC voltage and the other two have -DC voltage. Together these 2 pairs creates an oscillating electric field, which makes it possible to filter out specific molecules to go through the system.

Question 18

Ionization mode directly affects the ionic species generated.
True or false

Answer 18

True

Question 19

Which ionization mode would be useful for investigating small compounds (50-500Da)
EI, ESI or/and MALDI

Answer 19

EI and ESI

Question 20

Which ionization mode would be useful for investigating medium sized compounds (500-5000Da)
EI, ESI or/and MALDI

Answer 20

ESI and MALDI

Question 21

Which ionization mode would be useful for investigating large compounds (>50000Da)
EI, ESI or/and MALDI

Answer 21

ESI and MALDI

Question 22

Assuming an identical charge state of +1, which molecule would reach the detector first in reflector mode TOF analysis?
Lighter or heavier molecule

Answer 22

The lighter molecule

Question 23

A quadrupole can provide:
High resolution or low resolution mass spectra

Answer 23

Low resolution mass spectra

Question 24

What is an iontrap?

Answer 24

An ion trap is a type of mass analyzer that uses electric (and sometimes magnetic) fields to trap ions in space. It allows for Storage, isolation, and fragmentation of ions. It is a method with high sensitivy and is therefore good for small samplesizes.

Question 25

What is an orbitrap?

Answer 25

An Orbitrap is a high-resolution mass analyzer used in mass spectrometry. It traps ions in an electrostatic field, where they oscillate around a central electrode.The frequency of this oscillation depends on the ion’s mass-to-charge ratio (m/z).A Fourier Transform is used to convert the signal into a mass spectrum. Orbitraps provide very high mass accuracy and resolving power, ideal for analyzing complex mixtures like peptides and metabolites.

Question 26

How can the ions be detected?

Answer 26

Through electron multipliers.When an ion strikes the detector surface, it releases one or more secondary electrons. These electrons are accelerated and hit additional surfaces inside the multiplier, releasing even more electrons at each stage. This cascading effect amplifies the signal, producing a measurable current pulse that corresponds to the ion’s presence and intensity.

Question 27

A linear ion trap can by itself also work as a mass analyzer True or false

Answer 27

True

Question 28

An orbitrap determines m/z by determining: -The amplitude of ioninc oscilation along the central electrode axis -The amplitude of ioninc oscilation perpedicularly to the central electrode axis -The frequency of ioninc oscilation along the central electrode axis -The frequenzy of ioninc oscilation perpedicularly to the central electrode axis

Answer 28

The frequency of ioninc oscilation along the central electrode axis

Question 29

Which mass analyzer has the highest resolution and mass accuracy? Quardupole, Orbitrap or TOF

Answer 29

Orbitrap

Question 30

You achieve the highest sensitivity by measuring: - Direct ion current - Generating secondary electrons - Measuring ionic absorbance of light at a given wavelength

Answer 30

Generating secondary electrons

Question 31

What does hybrid instruments consists of and why is it an advantage to use?

Answer 31

Hybrids consists of at least two mass analyzers and is used to control fragmentation instead of avoiding it.

Question 32

How can you reduce fragmentation to increase the signal of precursor ions in mass spectrometry?

Answer 32

- Lower the electron energy in the electron ionization (EI) source by reducing the ion source potential → less fragmentation → more intact precursor ions reach the detector. - Alternatively, use a soft ionization method (e.g., ESI or MALDI), which causes much less fragmentation than EI.