2.1.4 Determining masses using mass spectrometry Flashcards
what is a mass spectrometer?
a piece of apparatus that can be used to find out about molecules
what can a mass spectrometer be used to find out?
-identify a new compound
-find the relative abundance of each isotope of an element
-determine structural information about molecules
how does a mass spectrometer determine the mass of a molecule/isotope?
it causes substances to become positive ions and then measures the mass-to-charge ratio.
what is a mass spectrum similar to?
a complex bar graph
what does the mass spectrum give info of?
of the abundance of ions present in sample
what is on the y axis on a mass spectrum?
percentage abundance
what is on the x axis on a mass spectrum?
mass to charge ratio
how is the mass to charge ratio labelled on the mass spectrum?
m/z
what are the three steps in analysing a mass spectrum?
-the number of bars represents the number of isotopes
-the number under the bar represents the isotopic mass
-the number above the bar represents the relative abundance
how to work out the relative abundance if there isn’t any values or no scale on the y axis?
measure each line and use the formula height of singular isotope/ heights of the isotopes x100
what can the relative abundance and individual isotopic masses be used to find out?
the relative atomic mass of the sample
what is the formula for relative atomic mass?
(isotopic mass of A x abundance)(‘B”) (“C”) / 100
in A level mass spectrometry, what is charge always?
1
as charge is always 1, what is mass + charge equal to?
mass
what are the four steps of mass spectrometry?
-ionisation
-acceleration
-deflection
-detection
what is the ionisation step of mass spectrometry?
molecules/isotopes become positive ions (after being placed in a volatile substance)
what is the acceleration step of mass spectrometry?
the ions are accelerated so they have the same kinetic energy
what is the deflection step of mass spectrometry?
the ions are then deflected by a magnetic field, depending on their masses and their charges
in the deflection stage, how are the ions deflected?
the lighter they are, the more they are deflected and the more charge they have (the electrons they lost), the more they are deflected
what happens in the detection stage?
The beam of ions passing through the machine is detected electrically and a mass spectrum is produced
how does a mass spectrometer determine the mass of a molecule/isotope?
by measuring mass-to-charge ratio
why is there a need for a vacuum?
the ions produced in the ionisation chamber must have a free run through the machine without hitting air molecules.
