mass spectroscopy

Question 1

name the 4 stages in a time of flight mass spectroscopy

Answer 1

ionisation
acceleration
drift
detection

Question 2

explain what happens during the ionisation stage in terms of electron impact

Answer 2

high energy electrons are fired at sample causing a electron to be removed creating a positive ion

Question 3

explain what happens during the ionisation stage in terms of electrospray

Answer 3

sample is fired through a fine needle so it gains a proton to form a H+ ion

Question 4

electron impact equation

Answer 4

X (g) —-> X+ (g) + e-

Question 5

electrospray equation

Answer 5

X (g) + H+ —-> XH+ (g)

Question 6

explain what happens during the acceleration stage

Answer 6

electrons accelerated by electric plates so they have the same kinetic energy

Question 7

explain what happens during the drift stage

Answer 7

heavier ions travel more slowly through tube

Question 8

explain what happens during the detection stage

Answer 8

the size of the current is proportional to the number of ions (draw a graph - shows mass and abundance of particles)

positive ions hit the negative plate and produce an electric current

Question 9

define relative atomic mass (Ar)

Answer 9

average mass of 1 atom divided by the 1/12 mass of 1 atom of carbon 12

Question 10

define relative molecular mass (Mr)

Answer 10

average mass of molecule divided by 1/12 mass of 1 atom of carbon 12

Question 11

why are mass spectrometers used

Answer 11

to determine the mass of seperate atoms (or molecules)

or to identify the different isotopes that make up an element

Question 12

why is a time of flight mass spectrometer kept under a vacuum

Answer 12

to prevent the ions that are produced colliding with molecule’s from the air

Question 13

what happens after the ions have been detected in time of flight mass spectrometry

Answer 13

data analysis

the signal from the detector is passed to a computer which generates a mass spectrum

Question 14

what is on the x and y axis for a mass spectrum graph

Answer 14

x axis - mass/charge ratio

y axis- relative abundance

Question 15

what is he difference between high resolution mass spectrometry an low resolution mass spectrometry

Answer 15

high resolution mass spectrometry - measuring relative atomic mass to 5 decimal places

low resolution mass spectrometry - measuring relative atomic mass to 1 decimal place