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# Gas Chromatography

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## Matt Cannon

on 4 April 2017

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#### Transcript of Gas Chromatography

Gas Chromatography
Here is where your sample for analysis is injected into the GC.

It's not advisable to use large compounds in GC as it can lead to blockages forming in the column
Different types of carrier gas can be used but Neon is a good choice as it is unreactive, helium or nitrogen are also used.

The carrier gas is the
mobile phase
in GC.
In the oven is a column, which contains an extremely thin layer of either a liquid, polymer or inert solid. This is the
stationary phase!

As samples are carried through the column by the carrier gas they interact with the sides of the column. The more they interact the longer it takes for them to get through the column (elute).

The oven is there to keep samples gaseous. It's temperature can be altered in order to ensure the sample always remains this way

Housed inside the oven is the column
The detector is there to recognise when samples elute. This information is then plotted onto a graph
How can Gas Chromatography be used in Quantitative Analysis
Area Percent Method
This technique is the simplest but also the most prone to errors. It assumes that the detector responds equally to all samples however this is not strictly true.
To calculate area percent firstly take the area of the peak and then divide it by the sum of all the areas of analytes in the chromatogram
For cholesterol
peak area
total peak area
____________
320
850
____
=
=
0.38
therefore 38% of the sample is cholesterol
Single Point External Standard
To do this you have to use the following two equations
response
factor
=
peak area
__________
sample amount
amount of
analyte
=
peak area
________
response factor
Firstly analyse a sample containing a known amount of analyte or analytes and record the peak area. \use this to calculate the response factor

Inject a sample with the unknown analyte concentration and record the peak area. Use the equation to calculate the amount of analyte
An injection containing benzene at a concentration of 1,000 micrograms/ml is made and results in a peak area of 50,000. Calculate the response factor for benzene.

An injection of the sample with the unknown concentration of benzene has a peak area of 37,000. Calculate the amount of benzene present
Multiple Point External Standard
For this method we assume that analyse reponse is linear over a range of concentrations
Best used when concentration range is large or single method is not linear
Place in the GC solutions of known concentration and plot peak areas on a graph.

Then run your unknown concentration and where it breaks the line of best fit will tell you the solution concentration
Single Point Internal Standard
An internal standard can be used which has a predictable retention time and area, this way if abnormalitites occur they can be detected
The SPIS method requires at least two analyses. The first of which contains a known amount of internal standard and a sample your analysing. You would then calculate the response factor using the following the equation
Internal Response
Factor
=
area of internal standard x amount of compound of interest
_________________________________________
amount of internal standard x area of compound of interest
Then add a known amount of the internal standard tot he sample containing analytes of unknown concentrations. Then calculate the amount of unknown analyte using the following equation
amount of compound
of interest
=
amount of internal standard x area of compound of interest x Internal Response Factor
__________________________________________________________________
area of internal standard
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