Flashcards
Mass Spectrometry
Cards in this deck (21)
- 1What is a mass spectrometer?A machine that can be used to analyse elements or compounds.
- 2Define mass spectrometry.An analytical technique that gives information on relative mass and relative abundance of atoms or molecules in a sample.
- 3What can a mass spectrometer give you information about?Relative atomic mass, relative molecular mass, and the relative abundance of isotopes.
- 4What are the four things that happen when a sample is squirted into a time of flight (TOF) mass spectrometer?Electrospray ionisation, acceleration, ion drift and detection.
- 5What happens in electrospray ionisation (mass spectrometry)?The sample's dissolved in a polar solvent and pushed through a small nozzle at high pressure. A high voltage is applied to it, causing the particles to lose an electron. The ionised particles are separated from the solvent, leaving a gas made up of positive ions.
- 6What happens in acceleration (mass spectrometry)?The positive ions are accelerated by an electric field. This gives the same kinetic energy to all the ions. The ions with a lower mass/charge ratio experience a greater acceleration – they’re given as much energy as heavier ions but they’re lighter so accelerate more.
- 7What happens in ion drift (mass spectrometry)?The ions leave the electric field with a constant speed and constant kinetic energy. They enter a region with no electric field and drift through it at the same speed as they left the electric field. So the ions with lower mass/charge ratios will be drifting at higher speeds.
- 8What happens in detection (mass spectrometry)?As ions with a lower mass/charge ratio travel through the drift region at higher speeds, they reach the detector in less time than ions with a higher mass/charge ratio. The detector detects the current created when the ions hit it and records how long they took to pass through spectrometer. This data is then used to calculate the mass/charge values needed to produce a mass spectrum.
- 9What does a TOF mass spectrometer look like and where do each of the four stages happen?
- 10What is a mass spectrum?A chart produced by a mass spectrometer which can give you information about the relative masses and relative abundances of particles in a sample.
- 11If the sample is an element what does each line on a mass spectrum represent?A different isotope of the element.
- 12What does the y-axis on a mass spectrometer give?The abundance of ions, often as a percentage (percentage abundance).
- 13For an element what does the height of each peak give?The relative isotopic abundance.
- 14Define relative isotopic abundance.The relative amount of each isotope present in a sample of an element.
- 15What are the x-axis units given as on a mass spectrometer?‘Mass/charge’ ratio
- 16What can you usually assume the x-axis is the same as? Why?The relative isotopic mass because the ions are mostly 1+ (and the x-axis is mass/charge).
- 17How can mass spectrometry be used to identify elements?Elements with different isotopes produce more than one line in a mass spectrum because the isotopes have different masses. This produces characteristic patterns which can be used to identify certain elements.
- 18How do you calculate the relative atomic mass, Ar, of an element from a mass spectrum?• For each peak, read the % relative isotopic abundance from the y-axis and the relative isotopic mass from the x-axis. Multiply them together to get the total relative mass for each isotope.
• Add up these totals.
• Divide by the total relative abundance (should be 100 if they are percentages). - 19How do you calculate relative molecular mass from a mass spectrum?A molecular ion, M+(g), is formed when 1 electron is removed from the molecule. This gives a peak in the spectrum with a mass/charge ratio equal to the Mr of the molecule.
- 20What can the relative molecular mass be used for?To help identify an unknown compound.
- 21What will the spectra be like if you have a mixture of compounds with different Mr values?You’ll get a peak for the molecular ion of each one.
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- A2 Chemistry Flashcards on Mass Spectrometry, created by Jasmine Bayliss-Dagg on 20/09/2017.
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- Jasmine Bayliss-Dagg
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