Retention time and system suitability

[pharma80]

Could you please help on defining system suitability criteria regarding retention time? I am used to work upon RSD < 1% regarding 6 replicate injections, but there is no evaluation provided in the current phamacopoeias. I assume it is a rational deviation, but no theoritical information is provided.

[tom jupille]

The rationale for 1% is essentially "because we can".

If you want to set a looser spec and you have the robustness data to back it up that should be OK (you may have to do some convincing of a reviewer). If you have a complex sample or close potential interfering peaks, then you might have to set your spec a bit tighter. You can't go too much tighter because many HPLC pumps only spec flow accuracy to something like 0.25%