mass spectrometry

Question 1

what is the mass spectrometry?

Answer 1

methods which gives accurate information about isotomic mass, abundance, and relative molecular mass of certain isotopes in an element

Question 2

what is a method of mass spectrometry?

Answer 2

time of flight

Question 3

what is stage 1 of TOF?

Answer 3

ionisation

Question 4

what are the two ways that a sample can be ionised?

Answer 4

electron impact and electrospray

Question 5

how is the sample ionised using the electrospray method?

Answer 5

a sample is dissolved in a volatile solvent (where it evaporates easily) and injected through a hyperdermic needle with a high voltage tip

Question 6

how are the particles in the sample ionised?

Answer 6

the particles are ionised by gaining an proton (H⁺) from the solvent as they leave the needle producing XH⁺ ions (ions with a single positive charge and a mass of Mr + 1)

Question 7

what is the equation for the ionisation of a sample using the electrospray method?

Answer 7

X(g) + H ⁺ –> XH⁺ (g)

Question 8

what is stage 2 of TOF?

Answer 8

acceleration

Question 9

where are the positive ions accelerated and why?

Answer 9

through an electric field in an ion drift so that they all have the same kinetic energy

Question 10

why do the positive ions need to have the same kinetic energy?

Answer 10

so the particles separate to their according masses

Question 11

what is the velocity of each particle dependant on?

Answer 11

dependant on it’s mass. lighter particles have a faster velocity and heavier particles have a slower velocity

Question 12

if particle is lighter will it reach the detector first?

Answer 12

yes, as the lighter particle has a faster velocity so it will reach the detector first

Question 13

what is the equation that links kinetic energy, velocity and mass?

Answer 13

ke= mv² / 2

Question 14

what is the equation for v²

Answer 14

d² / t²

Question 15

how to calculate the mass in kg of one ion (mass needed for TOF calculations)

Answer 15

Mr (which is in grams) / 1000 = kg
then ans / 6.022x10²³

Question 16

what is stage 3 of TOF?

Answer 16

detection

Question 17

what does the positive charged ions hit in order to be detected? why?

Answer 17

a negative plate to produce a electrical current as they gain electrons from the plate which generates a movement of electrons hence why it produces an electrical current

Question 18

why is the detector connected to produces the results?

Answer 18

the detector is connected to a computer which produces a spectrum

Question 19

how is abundance determined?

Answer 19

size of current is proportional to abundance

Question 20

what does a mass spectrum show?

Answer 20

the mass to charge ratio (m/z) and the abundance of each ion

Question 21

what does the m/z represent?

Answer 21

the mass to charge ratio. however, as the ions are produced by gaining an proton (1+ charge), the m/z is the mass of the ion

Question 22

what is another type of mass spectometery?

Answer 22

electron bombardment

Question 23

how is an ion form using the electron impact method?

Answer 23

the sample is hit using high energy electrons which leads to the sample molecule losing an electron

Question 24

what is the equation for the ionisation of a sample using the electron impact method?

Answer 24

X(g) + e⁻ –> X⁺ (g) + 2e⁻

Question 25

how are ions accelerated using an electromagnet?

Answer 25

• ions are accelerated and all have the same kinetic energy
• ions are deflected by a magnetic field according to their masses
  —-> the lighter the ion, the more the ion deflects.
• the amount of deflection depends on the number of positive charges on the ion
  —-> the more charged the ion is, the more the ion deflects

Question 26

what is the definition of relative atomic mass?

Answer 26

weighted average mass of an atom of a element relative to 1/12th the relative atomic mass of an atom of carbon 12

Question 27

what actually is the mass spectrometer?

Answer 27

a vaccum

Question 28

why is the mass spectrometer a vaccum?

Answer 28

prevent the ions from colliding with the molecules in the air