Mass spectrometer

Question 1

What is the first stage of mass spectrometer ?

Answer 1

ionisation

Question 2

Why does a sample need to be ionised before entering a mass spectrometer ?

Answer 2

mass spectrometry measures the mass of charged particles, only ions will be detected,

Question 3

What are the two methods of ionisation in mass spectrometer?

Answer 3

Electron impact and electrospray ionisation

Question 4

how does electrospray ionisation work ?

Answer 4

— in this method the sample is dissolved in a solvent and pushed through a small nozzle at high pressure. A high voltage is applied to it, causing each particle to gain an H+ ion. The solvent is then removed, leaving a gas made up of positive ions.

Question 5

How does electron impact ionisation work ?

Answer 5

— in this method, the sample is vaporised andan ‘electron gun’ is used to fire high energy electrons at it. This knocks
one electron off one each particle, so they become +1 ions.

Question 6

What is the 2nd stage of mass spectrometery ?

Answer 6

Accelaration

Question 7

Explain acceleration in mass spectrometer ?

Answer 7

The positive ions are accelerated by an electric field. The electric field gives the same kinetic energy to all the ions. The lighter ions experience a greater acceleration — they’re given as much energy as the heavier ions,
but they’re lighter, so they accelerate more.

Question 8

what is the eqaution for electron impact ionisation ?

Answer 8

X(g) + e– -> X(g) + 2e–

Question 9

when is electron impact ionisation used ?

Answer 9

low formula mass

Question 10

what is the equation for electrospray impact?

Answer 10

X(g) + H+ -> XH+(g)

Question 11

when is electropray ionisation used ?

Answer 11

for high formal mass

Question 12

What is the formula for kinetic energy ?

Answer 12

KE =𝟏/𝟐𝒎𝒗^𝟐
KE = kinetic energy of particle (J)
m = mass of the particle (kg)
𝑣 = velocity of the particle (m s–1
)

Question 13

how would you rearrange the kinetic energy formula to obtain velocity ?

Answer 13

𝒗 = √𝟐𝑲𝑬/m

Question 14

what is the third stage of mass spectrometer ?

Answer 14

Ion drift /flight tube

Question 15

what happens in ion drift?

Answer 15

Next, the ions enter a region with no electric field. They drift through itat the same speed as they left the electric field. So the lighter ions will be drifting at higher speeds.

Question 16

give the two equations and the units for time ?

Answer 16

𝒕 =𝒅/𝒗
𝒕 = 𝒅√𝒎/𝟐𝑲E
t = time of flight (s)
d = length of flight tube (m)
𝑣 = velocity of the particle (m s–1
)
m = mass of the particle (kg)
KE = kinetic energy of particle (J)

Question 17

What is the fourth stage of mass spectrometry ?

Answer 17

detection

Question 18

how does detection work ?

Answer 18

Because lighter ions travel through the drift region at higher speeds, they
reach the detector in less time than heavier ions. The detector detects the current created when the ions hit it and records how long they took to pass through the spectrometer. This data is then used to calculate the mass/charge values needed to produce a mass spectrum

Question 19

what is a detector ?

Answer 19

a negatively charged electric plate

Question 20

why may their be small peaks in a mass spectra ?

Answer 20

electron impact ionisation was used and fragments have fragmented

Question 21

what does the hight of each peak in a mass spectrometer mean ?

Answer 21

the relative isotopic abundance

Question 22

what is the y axis in a mass spectrum ?

Answer 22

% abundance

Question 23

what is a x axis in a mass spectrum?

Answer 23

mass/charge ratio

Question 24

how do you identify a element from a mass spectrum ?

Answer 24

Step 1: For each peak, read the % relative isotopic abundance from they-axis and the relative isotopic mass from the x-axis. Multiply them together to get the total relative mass for each isotope.
ƒ Step 2: Add up these totals.
ƒ Step 3: Divide by 100 (since percentages were used).
this will give you an Ar which you can fond the mass from

Question 25

how do you identify the element from the mass spec if the relative abundance is not in percent ?

Answer 25

don’t divide by 100

Question 26

how do u find the Mr of a molecule on a mass spectra?

Answer 26

the mass/charge ratio of its peak

Question 27

How do u calculate distance

Answer 27

Velocity xtime