Chromatography Forum

Hi Tryfan

I have printed out your chromatograms so I can see them more clearly - your peak 14 is not good, the extra area at the front and the tail could easily account for the discrepancy. One way round this would be to try calculating by height which avoids this problem.

To further resolve this problem it would be useful to have full details of the calculation as I can't fully understand how the final figure is arrived at.

It would be more helpful to see "typical" chromatograms run per method directions from both labs, preferably of the same sample.

Out of interest or ignorance, surely if the retention times were different, the areas under the peaks would still be comparable with others?

Only to a certain extent. If you are dealing with overlapping elution of different analytes, things are going to get worse as you stray farther away from the low point in the VanDeemter curve for your setup.

You have not yet told us about the instruments in use or the kind of column. Based on the chromatograms, it appears to be an isocratic method.

Hi Tryfan

you say:

Except in the method they gave me it has a trace which is the same as what i get, not what they get now

can you please specify what the same is?
is it the retention time, the peak shape?
does it look like the picture you provided here?

i think that you should show us a chromatogram of what you get when you do exactely according to their method.
can you say exactely what you changed in order to get to the picture that you showed us already?

the details of your method would be nice and also like DR said the type of instruments used by both labs.
so as to not over look any thing could you also provide the sample preparation method?

not as to put you in the blues too much, but in some labs they don't stick to their own protocols, they twick them sometime a bit because nobody can catch them on it and they don't want to revalidate; but they will never tell you about it; hopefully this is not your case

Hi Tryphan

Have you made any progress with resolving your problem