Chromatography
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What does GC stand for
Gas chromatography
In a GC experiment, what is measured
Time
If on a chromatography paper the sample travels far, what is the time recorded if the sample was tested using a GC
Fast time
Reading the graph, with the time for the molecules to pass through the GC, what do the widths of the peaks show
Concentration of molecule
What are the 2 things that chromatography can be used for
-Small scale analysis - Bigger scale purification
In all types of chromatography, what are the 2 phases
• Mobile • Stationary
What does TLC stand for
Thin Layer Chromatography
If a component of the compound has a stronger absorption to the stationary phase, does it more or less time for the component to migrate up the plate
More time, it’s slower
What is the mobile phase in gas chromatography
Gas, unreactive
What is the time taken for each component of a sample to travel through the tube known as
The retention time
In gas chromatography, what is the stationary phase
A liquid absorbed onto an inert solid support
If a component of compound is more soluble, what happens to the retention time
Longer retention time as the component would spend more time in the stationary phase
If the stationary phase is more polar, are polar or non-polar components more soluble
Polar
If compounds have similar functional groups, what are their retention times like
Similar
Reading a gas chromatogram, what does the area under the peak proportional to
The amount of each compound
If we want to know the actual amount of a substance present in a sample, what do we have to do to the GC instrument
Calibrate it
What are the steps when calibrating a GC instrument
• Inject a series of samples containing known concentrations • Measure the peak area • Plot a calibration curve • Run the unknown sample and compare to the calibration curve. • Concentration of sample can then be estimated
What is a GC-MS
Combining Gas Chromatography with Mass Spectrometry
What are 3 advantages of GC-MS
• Very good resolution • Can operate with very tiny amounts of sample mixture • A very large database of mass spectra, so good chance of positive identification
What are 3 limitations of GC-MS
• Similar compounds often have similar retention times so difficult to separate and identify • Unknown compounds in mixture have no reference retention time or mass spectra matching • Equipment is relatively sophisticated and expensive
What are some uses for GC-MS
• Forensic science- analysis tiny traces of matter • Testing organic pollutants • Airport security - detecting explosives • Space missions - looking for life on other planets