CbD - Gas-liquid chromatography Flashcards
What is gas-liquid chromatography good for?
Separating and identifying components.
What is chromatography used for?
To separate stuff in a mixture.
What can you do once stuff has been separated out in a mixture using chromatography?
Identify the components.
What are the symbols/shorthand way for writing gas-liquid chromatography?
GLC
What are the 2 phases in chromatography?
A mobile phase
A stationary phase
How many phases are there in chromatography?
2
What is a mobile phase?
Where the molecules can move. This is always a liquid or a gas.
What state is the mobile phase always in in chromatography?
Liquid or gas.
What is a stationary phase?
Where molecules can’t move. This must be a solid, or a liquid on a solid support.
What state must the stationary phase be in in chromatography?
This must be a solid, or a liquid on a solid support.
What is the relationship between the mobile and stationary phase in chromatography?
The mobile phase moves through the stationary phase.
What happens as the mobile phase moves through the stationary phase?
The components in the mixture separate out between the phases.
What are gas-liquid chromatograms great for showing?
The proportion of esters in oils used as binding mediums in paint.
Because gas-liquid chromatograms are great for showing the proportion of esters in oils used as binding mediums in paint, what does this help to do?
Identify the oil present.
Why are gas-liquid chromatograms great for showing the proportion of esters in oils used as binding mediums in paint?
Only a very small sample of paint is needed.
What is the stationary phase in GLC?
A solid, or a viscous, high boiling point liquid (such as an oil), which coats a porous support inside a long tube.
What is the tube with the stationary phase like in GLC?
Coiled to save space, and built into an oven.
What is the tube also known as in GLC?
A column (even though it is coiled).
What is the mobile phase in GLC?
An inert (unreactive) carrier gas such as nitrogen or helium.
How do you carry out GLC?
- The sample to be analysed is injected into the stream of carrier has, which carries it through the tube and over the stationary phase.
- The components of the mixture constantly dissolve in the stationary phase, evaporate into the mobile phase and then redissolve as they travel through the tube.
What happens to the components of the mixture as GLC is happening?
The components of the mixture constantly dissolve in the stationary phase, evaporate into the mobile phase and then redissolve as they travel through the tube.
What does the solubility of each component in the mixture determine?
How long it spends dissolved in the stationary phase and how long it spends moving along the tube in the mobile phase.
What about each component in the mixture determines how long it spends dissolved in the stationary phase and how long it spends moving along the tube in the mobile phase?
The solubility of each component in the mixture.
Explain how substances with a high solubility will spend their time in GLC
They will spend more time dissolved, so will take longer to travel through the tube to the detector than one with a lower solubility.
Which level of solubility would substances that spend more time dissolved, so will take longer to travel through the tube to the detector have?
A higher solubility.
What do GLC chromatograms show?
The proportions of the components in a mixture.
What does a GLC chromatogram look like?
A series of peaks at the times when the detector senses something other than the carrier gas leaving the tube.
What can the peaks on a chromatogram be used for?
To identify the substances within a sample and their relative proportions.
What is the time taken to reach the detector in GLC called?
The retention time.
What is the retention time in GLC?
The time taken to reach the detector.
What does each peak on a chromatogram correspond to?
A substance with a particular retention time.
How are retention times measured?
From zero (in time) to the centre of each peak.
Where can you use retention times/what are they useful for?
They can be looked up in a reference table to identify the substances present.
What has to be the same when you look up retention times in a reference table to identify substances present?
The conditions of the test and reference table are the same.
What can you look up in a reference table to identify the substances present from GLC?
Retention times.
What do you have to be careful about when identifying substances from retention times?
Similar compounds often have similar retention times, so they’re difficult to identify accurately.
What is the area under each peak on GLC chromatograms proportional to?
The relative amount of each substance in the original mixture.
What are the axis on a GLC chromatogram?
X-axis = Time/min
Y-axis = Recorder response
What can GLC be combined with?
Mass spectrometry
Why is it good pairing GLC and mass spectrometry?
GLC is very good at separating a mixture into its individual components, but not so good at identifying those components.
Mass spectrometry, however, is great at identifying unknown compounds, but would give confusing results from a mixture of substances.
So putting these two techniques together gives an extremely useful analytical tool.
What is gas-liquid chromatography-mass spectrometry (GLC-MS)?
Combines the benefits of GLC and MS to make a super analysis tool.
How is GLC-MS used/how is it carried out?
A sample is separated using GLC, but instead of going to a detector, the separated components are fed into a mass spectrometer. The spectrometer produces a mass spectrum for each component, which can be used to identify each one and show what the original sample consisted of.
