Mass spec

Question 1

MS requires generation of analyte ions in order to measure the relative mass of molecules. True or false?

Answer 1

True

Question 2

What is on the x and y axis?

Answer 2

Y is abundance of each ion

X is m/z ratio

Question 3

What are the four major stages of MS?

Answer 3

sample vaporisation
ion generation
ion separation
ion detection

Question 4

What are the three ways in which sample volatilisation can be achieved?

Answer 4

Heat
Placing sample in a vacuum
Using fast atom bombardment

Question 5

How can sample ionisation be achieved?

Answer 5

Bombarding the volatilised molecules with electrons from an electron gun. This will knock an electron out of the molecule, leaving it with a positive charge. Charged plates then accelerate the ionised molecules into the deflection chamber

Question 6

In electron impact ionisation, the sample is vaporised by heat. True or false?

Answer 6

True

Question 7

In electron impact ionisation, how is ionisation achieved?

Answer 7

By bombarding the volatilised molecules with an electron beam

Question 8

When an analyte molecule loses an electron, does its mass change?

Answer 8

No

Question 9

In electron impact ionisation, what are the fragments analysed based on?

Answer 9

mass to charge ratio

Question 10

How does chemical ionisation work?

Answer 10

Uses a stream of electrons to ionise a reagent gas (ammonia or methane). The ionisation of the reagent gas produces a strong acid. Volatilised analyte molecules are ionised by strong acid via protonation

Question 11

Electron ionisation and chemical ionisation are gentle methods and produce very little fragmentation. True or false?

Answer 11

False - not gentle methods and produce a lot of fragments

Question 12

Electron ionisation and chemical ionisation are suitable for small volatile molecules with molecular weight more than 1000 Da. True or false?

Answer 12

False - less than 1000 Da

Question 13

What atom does fast atom bombardment involve?

Answer 13

Xe

Question 14

What is the role of the matrix in fast atom bombardment?

Answer 14

Protect the analyte from fragmentation

Question 15

In FAB, do analyte molecules need to be evaporated beforehand?

Answer 15

No - bombardment by Xe atoms has dual action:
desorption of analyte molecules into gas phase and
ionisation

Question 16

FAB only generates positively charged ions. True or false?

Answer 16

False - generates both positive and negative ions

Question 17

Does the molecular weight of molecule change in FAB?

Answer 17

Yes - loss/gain of proton will change mass as protons have a weight

Question 18

Is FAB a gentle technique? Does it produce fragments?

Answer 18

Yes, a gentle technique with very little fragmentation

Question 19

FAB is suitable for the analysis of molecules up to 6000 Da. True or false?

Answer 19

True

Question 20

In FAB, energy transfer takes place from the matrix to Xe atoms. True or false?

Answer 20

False - from Xe to matrix

Question 21

What is the main difference between FAB and MALDI?

Answer 21

In MALDI, energy transferred from laser beam to matrix, whereas in FAB, energy is transferred from Xe to matrci

Question 22

FAB is a more expensive technique than MALDI, True or false?

Answer 22

False

Question 23

MALDI is suitable for biomolecules of up 500,000 Da. True or false?

Answer 23

True

Question 24

What is the role of the pH modifier in electrospray ionisation?

Answer 24

to produce ions - this will determine whether ionisation proceeds via protonation or deprotonation

Question 25

In which type of ionisation is the analyte dissolved in a mixture of organic solvent and water?

Answer 25

Electrospray ionisation

Question 26

In electrospray ionisation, a high voltage is applied to the capillary. Why?

Answer 26

To disperse the droplets into the air

Question 27

The droplets formed in electrospray ionisation are big, how are they diminished in size and why is this done?

Answer 27

a warm gas is applied (nitrogen) - creates smaller ions which are easier to ionise

Question 28

Electrospray ionisation is used for non-polar analytes. True or false?

Answer 28

False - used for polar analytes

Question 29

Atmospheric pressure chemical ionisation is similar to electrospray ionisation in that an organic solvent and a pH modifier is used. True or false?

Answer 29

True

Question 30

APCI is more effective at analysing less polar species than electrospray ionisation. True or false?

Answer 30

True

Question 31

The advantage of APCI is that the molecular mass range is typically less than 2000 Da. True or false?

Answer 31

False - this is a disadvantage

Question 32

Out of all the ionisation techniques, which one creates the most fragmentation?

Answer 32

Electron impact ionisation, followed by chemical ionisation

Question 33

Why does fragmentation take place?

Answer 33

Because the molecular ion produced by ionisation is in an excited state. This corresponds to excess vibrational energy leading to fragmentation

Question 34

Neutral species can be seen in MS. True or false?

Answer 34

False - only ionised species can be seen

Question 35

What does the process of ion separation involve?

Answer 35

once ionised, the analyte ions are separated by their interaction with an electrical or magnetic field in high vacuum

Question 36

How can the mass-to-charge ratio of fragments be changed?

Answer 36

By varying the strength of the magnetic field

Question 37

How are ions detected?

Answer 37

the positive ions and molecular fragments produced in the ionisation chamber are accelerated into an analysing tube. The path of the charged molecules is bent by an applied magnetic field

Question 38

In ion detection, high momentum ions are deflected the most and collide with the walls of the analyser. True or false?

Answer 38

False - deflected the least and collide with the walls. Low momentum ions are deflected the most, but too collide with the walls.

Question 39

Ions have to have the proper mass-to-charge ratio to collide with the collector and generate an electrical current. True or false?

Answer 39

True

Question 40

Analysis of MS involves re-assembling of fragments, after identifying their molecular structure, and working backwards to generate the original molecule. True or false?

Answer 40

True