Chromatography Forum

Hello everyone,

I would like to ask your opinion about results processing after GC analysis.
For each determination, I have done two injections.
After that, I've made the average of the obtained areas ( averaged analyte area, averaged internal standard area).
With average, I've calculated the ratio: analyte area / internal standard area and then the unknown concentration of the analyte.

Recently a colleague told me that I'm not doing it correctly, that it should be calculated individually (each injection separately to calculate the concentration of the analyte) and finally made the averaged of the 2 concentrations.
I do not understand where is the difference?
Is not the same? Is not the same error?
What do you think?
How do you proceed?


All the best,

Mermeth

Hi Mermeth

The internal standard corrects for analytical variation for one particular injection of one particular sample - which suggests that you should calculate analyte content individually and then take the means.

Nevertheless, a though experiment suggests that doing it your way should not make any difference.

Which then suggests that if it does make a difference then something has gone wrong somewhere. Handy QC.

Peter

Thank you very much Peter,

I'm more comfortable now, knowing that I haven't ruined all my work


Wish you wonderful moments,

Thank you very much Peter,

I'm more comfortable now, knowing that I haven't ruined all my work

You can only be sure of that if the results come out the same for both methods of calculation.

Peter

I agree with Peter and think you should plug in your numbers to verify. I thought this was an interesting question and would have thought that the two methods of calculation would give the same result. But I chose some arbitrary numbers and got two different answers. Maybe it's my math ????

Or it may have to do with the fact that....

A+B
X + Y

does not equal

A +
X

B
Y

Hi again,

Peter, I've done exactly as you suggested and the result was quite resembling.
I found sets of data that gave perfect match according to my first processing method.

Anyway, from now on, I'll do the calculation by every separate injection and in the end the average.

Thank you so much Peter, it is very helpful to me.

Thank you dlbenach,

Mermeth