Hello, I have some GC and PLFA questions!

[Methane-nin]

I am a student worker who is working with a Shimadzu GC-2010, and I am fairly new to Gas Chromatography. I have read up on many pages of information but there are two things that i have been trying to find that would really help me out.

The first regards area response. What is it and what units is area response measured in?

The second question regards PLFA analysis. I also will be doing PLFA analysis of soil samples, and I have been having tremendous difficulty in finding a way of searching for the correct Molecular Weights of various fatty acid methyl esters.
I will often get Peak Names for FAMEs that are impossible to find (I had been using the Sigma-Aldrich site to search for them, I only found a few of the compounds.)

The results I am given often only tell me the formula, but only in the FAME nomenclatures such as 16:0 or 13:0 ISO, with the chemical names not even given with many of the FAMEs I find.

[skunked_once]

This web site should answer many of your questions.
http://www.lipidlibrary.co.uk/GC_lipid/ ... index1.htm
I hope it helps!

[Methane-nin]

I had found that website before, but on closer inspection there was a link helping explain some more of the FAMEs I needed to know. Thanks for the link! Area response is still much of a mystery still...

[chromatographer1]

The area response goes back to the early methods of measuring the analytes eluting from a GC column. Some means of detection and an electrical signal output were established.

The signal was generated by means of an pre-amp and the output was generally in 0-10V or 0-1 volt maximum output.

The signal was recorded on a strip chart recorder (think of an EKG machine or an old time adding machine).

The peaks were 'integrated' by cutting the peaks out of the paper and weighing them, or by trianglation of the peak (1/2 height times width at base), a measurement of the "AREA" of the peak.

Later when computers (electronic integrators) were more common the height (µV) and the width (seconds) of the peaks were actually mathematically calculated more accurately. The dimensions of the area of the peak are still ...... µV x sec.

I hope this is helpful.

best wishes,

Rod

[Methane-nin]

Thanks for the information!

[Jumpshooter]

And to further elaborate on that explanation: Now, ALL analtytical software packages present this relationship in terms of "milli absorbance units" or mAU versus "minutes to the hundreths place". But still when you get back to it---if you were to cut out and weigh the paper---then you could do what our ancestors did---compute "weight of paper" vs. "amount of compound on column"!

[zokitano]

And to further elaborate on that explanation: Now, ALL analtytical software packages present this relationship in terms of "milli absorbance units" or mAU versus "minutes to the hundreths place".

I suppose you meant "milivolts units" instead of "mili absorbance units", because this is a GC question (presuming FID detection).

Regards