shift of retention time with new column

I did the annual maintenance of my HPLC 1200.

All tests are passed (pressure, leak, intensity).

I installed a new column to do the calibration of the HPLC and analyzed a standard to check the retention time.

The standard Tr is shifted from 0.7 min respect to normal Tr. I tested a second new column (from the same batch) and Tr is shifted from 0.7 min here again.

I tested an old column (with 1800 injections) changed in June 2019 and Tr is good.

In July, I had the same problem with 2 columns from the same batch: one had a shift of 0.4 min and the the other of 0.7 min) and I had to use the one with a 0.4 min shift since that time.


What protocole do you recommend to condition the new column ?  I do 100% methanol for one hour.

Is there a drift due  to zorbax columns fabrication ?

Before I change tubing and filters, what would you recommend to test ?


Many thanks for your help

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