Atomic Structure: Mass Spectrometer steps

Question 1

What are the 2 ways an sample can be ionised?

Answer 1

= electron impact
= electrospray ionisation

Question 2

How does electron impact work?

Answer 2

= sample is vaporized
= high energy electrons are fired at it from an electron gun (hot wire filament with a current running through it that emits electrons)
= knocks off one electron forming a +1 ion
(sometimes 2+ ions can form as it is completly random and 2+ ions cause the m/z to be halved).

Question 3

What can this technique be used for?

Answer 3

= elements and smaller molecules
= have a low formula mass
= the 1+ ion is known as a molecular ion

Question 4

What are fragments?

Answer 4

= usually appear in this method
= moleculor ion can break down into smaller fragments
= can be detected by mass spectrometer

Question 5

How does electrospray ionisation work?

Answer 5

= Sample is dissolved in a volatile solvent (E.G water or ethanol)
= injected through a fine hypodermic needle to give a fine mist (aerosol)
= tip of needle is attached to the positive terminal of a power supply
= particles are ionised by gaining a proton from the solvent
= produces a XH+ ion.

Question 6

What is electrospray ionisation used for?

Answer 6

= higher molecule mass substances
= ‘soft’ ionisation
= does not produce fragments

Question 7

How does acceleration happen?

Answer 7

= positive ions are accelerated using an electric field and are attracted to the negativley charged plate
= energy is transferred to the sample ions.
= ions with the same charge have the same kinetic energy

Question 8

What is the eqaution of kinetic energy?

Answer 8

= mass x velocity^2

Question 9

What does the velocity of the ions depends on?

Answer 9

= mass

Question 10

What happens during the flight tube stage?

Answer 10

= positive charge ions travel through a hole in the negative charge plate
= time of flight depends on the velocity which is dependant on the mass

Question 11

What happens to ions of different masses?

Answer 11

= seperate out

Question 12

The time it takes to travel through the flight tube is porportional to what?

Answer 12

= mass

Question 13

What hapens during the detection scene?

Answer 13

= positive ions hit a negativley charged plate
= when they hit they gain an electron so are discharged
= generates a movement of electrons and an electric current is measured

Question 14

What does the size of the current measure?

Answer 14

= Abundance of each isotope
= size of current it measure of number of ions hitting the plate

Question 15

What does the time it takes to hit the plate determine?

Answer 15

= Relative atomic mass
= porportional