time of flight mass spectrometry

Question 1

what can the mass spectrometer be used for

Answer 1

determine relative atomic mass (based on mass and abundance of isotopes) and relative molecular mass

Question 2

what does a spectrum show

Answer 2

mass/charge ratio against abundance

Question 3

what can the spectrum be used to find

Answer 3

relative isotopic abundance, atomic and molecular mass and structure of a compound

Question 4

molecular ion peak

Answer 4

peak with the highest mass

Question 5

base peak

Answer 5

peak with the largest abundance

Question 6

ions all particles analysed must be

Answer 6

1+ ions

Question 7

stages on mass spectrometry

Answer 7

1-ionisation
2-acceleration
3-ion drift
4-detection

Question 7

how does electron impact ionisation work

Answer 7

sample is vaporised and bombarded with high energy electrons fired from an electron gun. this knocks of one electron off each particle forming a 1+ ion

Question 7

types of ionisation

Answer 7

electron impact, electrospray

Question 7

what is electron impact ionisation suitable for

Answer 7

elements and substances with a lower molecular mass

Question 8

electron impact ionisation equation

Answer 8

X(g) –> X+(g) + e-

Question 9

how does electrospray ionisation work

Answer 9

sample dissolved in volatile solvent and injected through a fine hypodermic needle to create an areosole. needle attached to positive terminal of a high voltage power supply and particals gain a proton from the solvent as they leave the needle.

Question 10

electrospray ionisation equation

Answer 10

X(g) + H+ –> XH+(g)

Question 11

what type of substances is electrospray ionisation used for

Answer 11

substances with a higher molecular mass

Question 12

what do all ions have the same in acceleration

Answer 12

kinetic energy

Question 13

acceleration

Answer 13

the 1+ ions are accelerated using an electric field to the same kinetic energy. the same kinetic energy means velocity will depend in mass

Question 14

speed of light ions

Answer 14

faster

Question 15

speed if heavy ions

Answer 15

slower

Question 16

why does ionisation occur

Answer 16

so they be accelerated as they need to be attracted towards the negatively charged plate

Question 17

ion drift

Answer 17

the 1+ ions will pass through a hole in the negatively charged plate and move into the flight tube. The time of flight will depend on velocity

Question 18

detection

Answer 18

once pass through the mass spectrometer the ions will hit a negatively charged plate and gain an electron. this discharges to the ion and a current is produced, the size of this current is proportional to the abundance if ions hitting the plate and gaining an electron

Question 19

time of flight equations

Answer 19

mass = (Mr/Avagadros)/1000
kinetic energy=1/2mv2
velocity=distance/time

Question 20

equation units

Answer 20

kinetic energy= joules (J)
mass= kg
velocity=m/s
time of flight=seconds(s)
distance=m