By Budiy Susanto on Tuesday, July 13, 2004 - 05:36 am:

I have different retention time about 0.2 minutes for the same system and procedure, is it ok?
if not Ok, what can I do to solve this problem?

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By David Blais on Wednesday, July 14, 2004 - 11:48 am:

Do you mean you get a different retention time when you run the same procedure on the same system, but just on different days? If so, 0.2 minutes is not a huge difference, especially if you are running a gradient. Are all of your suitability requirements met?

Now, if you have a requirement in the procedure that states retention times must be within 0.1 minutes, then you have a problem. Please provide more information (isocratic or gradient? an increase or a decrease of 0.2 minutes? or a fluxuation back and forth? column held at a constant temp or uncontrolled temp?) so more detailed help can be given.

Regards,
David

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By James on Thursday, July 15, 2004 - 03:08 am:

and usually its a % retention time difference you want to look at

a peak coming out at 32.2 minutes instead of 32 is not a problem
but one coming out at 2.2 instead of 2minutes could be a problem.

as David says, its all to do with your run acceptance critera..
But if you are not running to GLP (or similar) and have no official limits, then it is your call.

James