01. Atomic Structure

Question 1

what are the stages of mass spectrometry

Answer 1

1. vaporisation
2. ionisation
3. acceleration
4. deflection
5. detection

Question 2

what happens in stage one of mass spectrometry

Answer 2

vaporisation:
the sample is heated, reduced in pressure or dissolved in a volatile solvent (e.g. dichloromethane)

Question 3

what happens in stage two of mass spectrometry

Answer 3

ionisation:
the sample is bombarded with a beam of high energy electrons, which knocks off an electron to ionise it. this forms postitive ions and sometimes breaks up molecules (fragmentation)

Question 4

what is fragmentation

Answer 4

the breaking up of molecules during the ionisation phase of mass spectrometry

Question 5

what happens in stage three of mass spectrometry

Answer 5

acceleration:
the ions are put in an electric field, which accelerates them to the same kinetic energy. this means that lighter molecules speed up and heavier molecules are slower (Ek=1/2mv^2)

Question 6

what happens in stage four of mass spectrometry

Answer 6

deflection:
the ions are placed in a magnetic field. this causes the faster and lighter ions to move around the bend in the mass spectrometer first, and then the slower and larger ions bend around the spectrometer last. the magnetic field slowly increases in strength over time as the faster molecules will require less strength to bend and the larger ones will require more.

time of flight:
the faster and lighter ions hit the detector first, and then the slower, heavier ones second

this is given that all of the ions are 1+, if they have more charge, they will be deflected more i.e. act as a lighter ion due to the m/z ratio

Question 7

what happens in stage five of mass spectrometry

Answer 7

detection:
the ions are detected electronically via electric or photographic, where and when they are detected can determine the mass to charge ratio of the ion/molecule/isotope. the resultant data is displayed as a mass spectrum

Question 8

what is the purpose of mass spec

Answer 8

• to identify molecular formulae,
• to identify the abundance of isotopes
• to identify the molecular masses and characteristics of a new compound
• based on their mass to charge ratio

Question 9

how do you interpret a mass spectrum

Answer 9

• position along the x axis gives atomic mass
• peak intensity gives its relative abundance
• the highest abundance is scaled to 100% and the other values are adjusted accordingly
• calculate average relative atomic mass by using the equation for