About RT

[aicmen]

Hi,members
There are several questions about RT puzzled me:
1,Many factors could effect RT,for example, RT in AM may be different from PM, so what is the accept criteria of the RT variation?
2,Is there any difference of the RT accept criteria between assay and impurity?
3,Where is the accept criteria from?
Thanks a lot, any comments would be welcome.

[tom jupille]

As with so many things, "it depends". The retention time must be reproducible enough to avoid misidentifying a peak. If it's a simple assay, (only one peak, for example), the retention time can vary by several percent and not cause a problem. If it's a complex sample, then retention times would need to be closer.

That said, look at the specification for flow rate accuracy/reproducibility on your pump. That will put a lower limit on the retention time reproducibility for your chromatography.