16.2- MASS SPECTROMETRY Flashcards
What is mass spectrometry used to do?
measure relative atomic masses of atoms
What is mass spectrometry the main method of?
main method for finding relative molecular mass of organic compounds
How do the compounds enter the mass spectrometer?
in solution
What happens to the compounds when it enters a mass spectrometer?
ionised + positive ions accelerated through instrument as beam of ionised molecules
What happens after the compound is ionised + positive ions accelerated through instrument as beam of ionised molecules in the mass spectrometer?
these then fly through instruments towards detector
What is measured of the compound by the mass spectrometer?
times of flight
What does the time of flight depend on?
mass to charge ratio m/z of ion
What is the output of the mass spectrometer presented as?
graph of relative abundance (vertical axis) against mass/charge ratio (horizontal axis)
Why is the horizontal axis (mass/charge ratio) effectively relative mass?
as charge on ion normally +1
What is the graph from the mass spectrometer called?
mass spectrum
What does mass spectra often show?
masses to nearest whole numbers only
What do mass spectrometers that can measure to three or four decimal places be used to do?
allow us to work out molecular formula of parent ion
What does high resolution mass spectrometry make us of the fact?
makes use of the fact isotopes of atoms don’t have exactly whole number atomic masses (except carbon-12 which is exactly 12 by definition)
What can be used to identify molecular formula from the accurate relative molecular masses from high resolution mass spectrometry?
computer database can be used to identify molecular formula from accurate relative molecular mass
