1.1 Mass spectrometry

Question 1

use of mass spectrometery

Answer 1

to determine all the isotopes present in a sample of element and to therefore determine the element

Question 2

why is mass spectrometry done under a vaccum?

Answer 2

So that air particles don’t ionise and register on the detector

Question 3

2 types of ionisatoin

Answer 3

Electron impact and electrospray

Question 4

What happens in electron impact?

Answer 4

• vaporised sample ejected at a low pressure
electron
•electron gun fires high energy electrons towards the sample
•electrons knock off to form positive ions
• e.g. Ti(g) –>Ti+ (G) + e-

Question 5

What happens in electrospray?

Answer 5

• sample is dissolved in a volatile, polar solvent
• ejected through a hypodermic needle producing aerosol
• needle has a high voltage
• as the sample molecule leaves the needle, it again s a proton
• the MH+ ions move towards the negative plate
• M(g) – H+ —> MH+(g)

Question 6

what is electron impact used for?

Answer 6

• lower formula mass

* can cause large organic molecules to fragment

Question 7

use of electrospray

Answer 7

• larger organic molecules

* the conditions mean fragmentation doesn’t occur

Question 8

What happens in accleration?

Answer 8

• positive ions accelerated towards the negative plate

* at a constant EK energy, velocity of each particle depends on mass

Question 9

Flight tube

Answer 9

• heavier particles take longer move through

* ions are determined by different flight times

Question 10

Detection

Answer 10

Electrons transfer from detector to form positive ions, producing current, where the current is proportional to the abundance pf the isotope

Question 11

largest peak on a mass spectra

Answer 11

this is equal to the relative molecular mass