When is the chromatography you are looking...

[gbalock]

not the chromatography you validated? An issue has come up recently where a method was being run in our QC lab and the retention of all of the components had shifted dramatically shorter. The analysts in the QC lab did not see this as a problem. What guidance can I give them to let them know how much variability is acceptable before the mehod is considered different?

[philippem]

you make your own acceptance criteria. So depending on the results during the method development ( not method validation) you can specify the time window for the retention.
If peaks elutes beyond that window the analyst should be warned. You could also program your software to do so: it will not recognize and not a report your product.

If you have a robust method , windows could be narrower.
But it depends also on the selectivity you obtain, how well resolved are your peaks.
If all retention times have shifted check your solventcomposition , pump flow

so set your criteria, and check look at your chromatogram before you report


regards

philippe

[DR]

Personally, I like to consider k (or N), resolution for my critical pair, tailing for the most tailing-prone peak and RSD. Depending on the type of method I'm working on (and how bad the chromatography is), I may just use one of these criteria, or all 4.

[Nalizer]

We consider the following factors: K prime, resolution between peaks, tailing factor and RSD. In a lot of case we specify mobile phase composition tolerating 2-5% variation. You can change retention by adjusting mobile phase composition. Tolerance for retention, resolution, tailing, and mobile phase composition should be specified in the method.

Temperature might play a critical role, too. We had once a method which was validated during summer time in one of the "warmer" places with "ambient temperature" and when we transferred method to Europe (Sweden) variation of retention time was around 6-8%.

Another possible reasons: proportional valves, equilibration, mobile phas e preparation,