Flashcards in Mass Spectrometry and Chromotography Deck (18):
What is chromatography used for?
To separate things in a mixture for identification of the components.
What are two types of chromatography?
Thin layer chromatography (TLC) Gas chromatography (GC)
What are the two phases in TLC and GC?
A mobile phase- where the molecules can move (always liquid or gas)A stationary phase- where the molecules can't move (must be a solid, or a liquid on a solid support)The mobile phase moves through the stationary phase, as this happens, the components in the mixture separate out between the phases.
In thin-layer chromatography (TLC)...
1) The mobile phase is a solvent, such as ethanol, which passes over the stationary phase.2) The stationary phase is a thin layer of solid powder, on a glass or plastic plate.
TLC separates components by...What is an Rf value?
AdsorptionRf value = distance travelled by spot/distance travelled by solvent
How does gas chromatography (GC) work?
The sample to be analysed is injected into the stream of carrier gas, which carries it through the tube over the stationary phase.The components of the mixture constantly dissolve in the stationary phase, evaporate into the mobile phase then redissolve as they travel through the tube.The solubility of each component determines how long it spends dissolved in the stationary tube and how long it spends moving along the tube in the mobile phase.The time taken to reach the detector is called the retention time.
What is a gas chromatogram?
This shows a series of peaks at time when the detector senses something other than the carrier gas leaving the tube.
How can a gas chromatogram be used to identify substances within a sample and their relative proportions?
1) Each peak on a chromatogram corresponds to a substance with a particular retention time.2) Retention times are measured from zero to the centre of each peak, and can be looked up in a reference table ot identify substances present.3) The area under each peak is proportional to the relative amount of each substance in the original mixture.
What are some limitations to gas chromatography?
Compounds which are similar will often have very similar retention times, so they're difficult to identify accurately.Can only be used to identify substances you already had reliable reference retention times for.
What is the mobile and stationary phase in gas chromatography?
The stationary phase is a viscous liquid, such as an oil, or a solid, which coats the inside of a long, coiled tube.The mobile phase is an unreactive carrier gas such as nitrogen or helium.
When is a mass spectrum produced?
When a sample of a gaseous compound is analysed in a mass spectrometer.
How does mass spectrometry help to identify compounds?
A sample is bombarded with electrons, causing other electrons to break off from the molecules.If the electrons remove a single electron from a molecules, the molecular ion, M+ peak is formed.To find the relative molecular mass of a compound you look at the molecular ion peak on its mass spectrum.The mass/charge value of the molecular ion peak is the molecular mass of the compound.The electrons also break up some of the molecules up into fragments.The fragments that are ions will show up on the mass spectrum giving a fragmentation pattern.
What is gas chromatography-mass spectrometry (GC-MS)?
Combines the benefits of gas chromatography and mass spectrometry.The sample is separated using gas chromatography but instead of going to a detector, fed into a mass spectrometer.
What is high pressure liquid chromatography (HPLC)?
1) In HPLC, the stationary phase is a solid that is packed into a glass column, like tiny silica beads.2) The mobile phase (a solvent) and the mixture are pushed through the column under high pressure, allowing the separation to happen much faster than if just dripped through. 3) As with GC, HPLC is more useful for separating mixtures than identifying hem- so its combined with mass spectroscopy.
What is GC-MS used in real life?
ForensicsAirport securitySpace probesEnvironmental analysis
Define Rf value
The distance moved by a solute / distance moved by solvent
Define retention time
The time between injection and emergence of a component.