shifting peaks

[Eduardo]

I'm currently using the AMINEX-87H (Mobile phase 4mM H2SO4 @35 C Guard column is outside the oven) column from BIO RAD and I have noticed (can't miss it really) the peak RT shifting (from 10.01min down to 8.90min). I checked for leaks (found one in the mixing chamber and fixed it) and the peak has stabilised at 8.9
I'm using a Shimadzu LC20 system.

Thank you for any help you might provide.

[Bruce Hamilton]

Well, assuming that you have fixed a leak on a chamber that was downstream from the pump, maybe the column flow has increased, resulting in reduced retention time?. Have you checked the flow at the detector or column outlet?

The other main reason for decreased retention time ( assuming your mobile phase composition and flow are constant ), is column temperature. The Biorad 87H is quite sensitive to column temperature, and a column temperature increase could also reduce the retention time.

Biorad offer an excellent publication in pdf form on their website on the 87H and friends, ( Bulletin 1928 - Guide to Aminex Columns ) and you should download it from their website.

Please keep having fun.

Bruce Hamilton

[HW Mueller]

Eduardo, are you trying to find an explanation as to why a leak caused a decrease in RT? To find an answer one would really need more info, for instance, what did you mix in your mixing chamber?

[tom jupille]

One possibility is that you had a leak all along.