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Topic: First GC problems  (Read 3718 times)

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Offline Synnr01

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First GC problems
« on: October 21, 2009, 10:59:58 AM »
I did a practical on gas chromatography (determination of fatty acid profiles for two cooking oils by gas chromatography) two weeks ago and now has come the time to write it up and complete certain tasks with the results. However I have a few problems.
I am attempting to calculate the DRF for the components present in my chromatogram.
The formula for this is:
A being peak area and C being concentration.
X being analyte and IS being internal standard.
I have the peak areas however I am unsure of the concentration of either.
My chromatogram states the mass of the IS and of the oil used as 260.3 mg and 493.7 mg respectively.
I do know how to work out concentration, however I don't know the volume that that mass is in.
Sample volume is 1 µl but that's not it, surely.
Help would be much appreciated.
Quote from: this is the method
0.511g of olive oil was put into a 100 mL round bottomed flask and 0.195 g of pentadecanoic acid was added. A solution was made up of 2.0 g sodium hydroxide dissolved in 100 mL methanoic acid and 10 mL of this solution was added to the reaction flask. A few anti-bumping granules were also introduced. The flask was attached to reflux apparatus and reflux was maintained for 20 minutes, until all globules of oil had disappeared. 10 mL boron trifluoride solution ( 12% w/v BF3 methanol) was slowly introduced to the by syringe via the reflux condenser and the system was maintained in reflux for a further 20 minutes. 15 mL hexane was then added in the same way and reflux continued for a final 5 minutes before being allowed to cool. Once the reaction mixture had cooled to 35°C (±5°C) the condenser was removed and 15 mL of saturated NaCl solution was added. The vessel was shaken and after settling, further saturated NaCl solution was added, bringing the solvent layer into the neck of the flask for easy removal. A sample of the less dense hexane layer was removed with a glass pipette and placed into the GC vial, filtering through cotton wool to take out any solid particles. The vial was labelled and the sample analysed with the GC.

Offline Synnr01

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Re: First GC problems
« Reply #1 on: October 22, 2009, 06:15:32 AM »
please. Any idea what I need to do??

Offline marquis

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Re: First GC problems
« Reply #2 on: October 23, 2009, 08:30:10 PM »
Can you define the DRF?  It looks like a response factor, although I'm not sure what the "D" is for.

A couple of other questions.  It looks like your internal standard is the pentadecanoic acid.  Is this correct? 

Your calibration may have been done with identical volumes, in which case a volume calculation may not be needed.  Here are a couple of questions.  You put in 511mg of olive oil and got out how much?  You put in 195 mg of pentadecanoic acid and got out how much?  How do the final weights of the unknowns relate to the amount put in originally?

A starting point.  Lets see where it goes from here.  Good luck.

Offline chiralic

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Re: First GC problems
« Reply #3 on: October 24, 2009, 01:22:27 PM »
DFR means Detector Response Factor


Offline Golden_4_Life

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Re: First GC problems
« Reply #4 on: January 07, 2010, 03:40:09 PM »
Suggest just using RF "response factor"---the use of "detector response factor" is a bit superfluous given that we all know that the Detector is the component of the system doing the "responding".

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