chemistry year 1 atomic structure

Question 1

What is a mass spectrometer?

Answer 1

• It is an analytical tool used to measure the mass-to-charge ratio (m/z) of ions.

Question 2

what is the most common mass spectrometer?

Answer 2

Time Of Flight (TOF) mass spectrometer.

Question 3

what are the four main parts of a TOF mass spectrometer.

Answer 3

1.Ionisation
2. Acceleration
3. Ion drift
4. Detection

Question 4

What is ‘Ionisation’?

Answer 4

• This process turns the sample into positive gaseous ions. There are two common methods of ionisation:
  Election impact- Used for elements and low Mr compounds.
• High energy electrons are fired at the sample from an electron gun.
• This knocks off one electron from each atom/molecule to form 1+ ion. X(g) = X+(g) + e-
  Electrospray ionisation - Used for high Mr compounds (e.g proteins)
• The sample is dissolved in a volatile (evaporates readily) solvent (eg methanol, water) and injected through a fine hypodermic needle as a fine spray into a vacuum in the ionisation chamber.
• A very high voltage is applied to the end of the needle where the spray emerges (the needle is positively charged)
• The particles gain a proton and become ions as a fine mist. x(aq) + H+(g) = XH+(g)
• solvent evaporates leaving 1+ ions.

Question 5

What is the ‘acceleration’ process?

Answer 5

• The positively charged ions are accelerated towards a negatively charged plate by an electric field, giving them identical kinetic energy. This means lighter ions will move faster than heavier ones.