Atomic Structure- Mass Spectrometry

Question 1

what is mass spectrometry used for

Answer 1

-finding abundance and mass of isotope
-finding relative molecular mass

Question 2

what happens in time of flight/ acceleration

Answer 2

ions are accelerated by electric field so they all have the same kinetic energy

Question 3

what are the 2 types of ionisation

Answer 3

electron impact and electrospray ionisation

Question 4

what happens in electron impact

Answer 4

-sample is vaporised
-electron gun fires high energy electrons at it
-electron gun is hot wire filament w/ current
-this knocks off 1 electron forming a 1+ion
-the 1+ ion are attracted towards negative electric plate

Question 5

equation for electron impact

Answer 5

X(g)—> X+(g) + e-

Question 6

what happens electrospray ionisation?

Answer 6

-sample is dissolved in volatile solvent
-injected through fine hypodermic needle to give fine mist (aerosol)
-tip of needle has high-voltage power supply
-particles are ionised by gaining a proton (H+ ion) from solvent and produce XH+ ions
-solvent evaporates while XH+ ions attracted to negative charge plate

Question 7

equation for electrospray ionisation

Answer 7

X(g)+ H+ —> XH+ (g)

Question 8

how is a h+ ion formed in electrospray ionisation

Answer 8

H has 1 electron and 1 proton. Ionisation looses an electron, leaving a positive charged proton

Question 9

when is electrospray ionisation used

Answer 9

-for substances with high molecular mass including biological molecules eg. proteins
-fragmentation rarely takes place

Question 10

when is electron impact used

Answer 10

-for elements and substances with low formula mass eg organic/inorganic molecules

Question 11

when molecules are ionised in electron impact, the 1+ion formed is known as

Answer 11

a molecular ion

Question 12

equation for kinetic energy

Answer 12

KE= 1/2 x m x v²

Question 13

equation for velocity

Answer 13

v= √ (2KE / m)

Question 14

lighter particles will have ____ velocity
heavier particles will have ____velocity

Answer 14

faster
slower

Question 15

what happens in stage 2 acceleration

Answer 15

positive ions are attracted to negative charged plate

Question 16

what happens in stage 3 flight tube

Answer 16

-positive ions travel thru a hole in negatively charged plate
-ToF depend on velocity and mass

Question 17

equation for time of flight

Answer 17

t= d/v

Question 18

rearrange time of flight equation with velocity

Answer 18

t= d √(m/2KE)

Question 19

what happens in stage 4 detection

Answer 19

-positive ions hit negatively charged plate
-positive ions get discharged by gaining electrons from plate
-this generates movement, causing an electric current to be measured
-size of current gives measure of no. of ions hitting plate

Question 20

what does the mass spectrum show

Answer 20

-mass to charge ratio (mass) (m/z)
-abundance of ion

Question 21

equation for relative atomic mass *******

Answer 21

(abundance 1x mass 1) + (abundance 2x mass 2) / mass 1+ mass2

Question 22

what does high m/z value in electron impact graph mean

Answer 22

means its from the molecular ion and gives relative molecular mass

Question 23

why are there small peaks in m/z graphs

Answer 23

molecular ions contain different isotopes

Question 24

why is a negative charged plate used

Answer 24

for positive ions to attract to negative plate

Question 25

how is abundance measured

Answer 25

abundance is proportional to size of current

Question 26

why would there be peaks on m/z graph

Answer 26

presence of isotopes

Question 27

in electrospray ionisation what should you do to the answer

Answer 27

-1 because it looses a electron in ionisation

Question 28

what is the state symbol every time for electron impact and why

Answer 28

(g) because it vaporises