internal standards in HPLC

[rerecicht]

I need some help in understanding the use of Internal standards and the use of them and what does it mean in the end.
I am working on AA in a revearse phase, Accq-tag method. and I am introducing internal Standard, noroleucine. I don't know much on the logistics with analyzing the internal standard. I will try to explain.
With one study I got about 20% difference lower of the nor internal standard, and I corrected it but one sample had a 60% difference it was corrected but what does that mean? Also I analyzed another study and it was completely different the 20% difference is higher on the other side the nor internal Standard.
Is there something wrong in the way I process the samples? Or is the internal standard the correction for that? Could some one explain a little, I feel I am doing something wrong?
Thanks Tracy

[tom jupille]

First of all, for an understanding of what internal standards do, look in the FAQ section:

http://www.lcresources.com/wiki/index.p ... alStandard

If that doesn't answer your question, please re-post with more details (e.g., what were the actual peak areas for the internal standard and analyte peaks in your calibrators and in some of the samples you are referring to.

[rerecicht]

Thanks for your help!
Tracy