mass spectrometry and chromatography Flashcards
what can mass spectrometry be used to identify?
mass spectrometry can be used to identify organic compounds. when an organic compound is placed in a mass spectrometer it is bombarded by high energy electrons and different electrons are knocked out of the organic molecule. this is called ionization.
what happens when a sample is bombarded with electrons ?
it forms a cation with an unpaired electron, M+* which is a radical
what is the molecular ion peak?
the peak on the mass spectrum with with the highest mass/charge ratio is called the molecular ion peak or M
what is the base peak
the highest peak
how does the stability of the cation affect the peak
the more stable the cation the higher its peak
what is chromatography ?
how are the components seperated
an analytical technique used to seperate components in a mixture
if the stationary phase is solid the components in the mixture are seperated by adsorption - how strongly each of the components interacts with the surface of the stationary phase
if the stationary phase is liquid the components in the mixture are separated by the relative solubility of each of the components in the mobile phase
in gas chromatography what are the phases?
stationary phase is a liquid or solid on a solid support
mobile phase is gas
what are the phases in tlc?
the stationary phase is a solid
the mobile phase is a liquid
Rf values
Rf values are used to compare the distance that acomponent moves compared with the distance that the solvent fron moves
Rf = distance moved by component/ distance moved by solvent front
Gas chromatography
Gasse chromatography (GC) is used to separate mixtures of volatile liquids. In GC, the components move through the apparatus at different speed, the retention time is the time it takes for a component to pass through the apparatus from the inlet to the detector. In gas chromatography each component produces a sepereate peak. Once separated, the components in the mixture can be identified. GC is so accurate that the area under the peaks indicates the relative amounnt of each component in a sample. It is used to measure the level of alchol in blood or urinine samplesd in court cases/
What are the limitations of gas chromatography
1) similar compounds have similar retention times
2) new compounds will have no reference times for comparison
what is GC-MS?
Mass spectrometry cobined with chromatography.
gas gromatography can be used to seperate the components of the mixture, then mass spectrometry can be used to positively identify each of the components either by analysing the mass spectra produced or by comparing the mass spectra with a spectral database
Where is GS-MS used?
1) in forensic science to identify drugs
2) in environmental analysis to monitor water quality
3) in airpot security to detect explosives
4) by space probes to analyse materials on other planets
