mass spectrometry Flashcards
what is a mass spectrometer
it separates molecules according to their charge and mass
what does mass spec allow you to do
identify a sample chemical by measuring its molecular weight
what are the three main parts of mass spectroscopy
the ionisation source
the analyser
the detector
describe the process of the time of flight mass spectrometry
sample inlet = gases/liquids are injected but solids are heated to vaporise them
ionisation area = a heated element produces high energy electrons. these electrons bombard any atoms or molecules in the sample and knock electrons out. positive ions (cations) are formed of the sample
acceleration area = a electric field is used to accelerate the ions so that they all have the same kinetic energy
drift region = here there is a vacuum (no air molecules for the ions to collide with and change their direction)
Since KE=1/2mv2 and all the ions have the same kinetic energy, therefore the lighter ions will move more quickly than the heavier ions
Ion detector = the lighter ions will reach the detector before the heavier ions. a computer turns this into a mass spectrum
what does a mass spectrometer show
the mass spectroscopy of an element
how to calculate relative atomic mass from the mass spectrum
1) multiply the abundance and the mass for each isotope. this gives the total mass of each isotope.
2) add up the totals
3) divide the total by 100
why are there many peaks shown in the mass spec
fragments of original molecule ions are formed in the ionisation chamber. if the fragments have a positive charge it will be accelerated by an electric field and detected.
what is the biggest peak in the mass spectrum
it is called the base peak which is the most intense peak. it is the most stable fragment
what does it mean if it is the most stable
its the most detectable and made most often.
how can you tell if the mass spec shows isotopes or fragments
if there is a 1 or 2 mass unit difference it is an isotope not a fragment
what information is given by the height of the peaks
intensity
what is the molecule ion known as
the original parent molecule
