By Bill on Friday, March 5, 2004 - 03:00 am:
I want to use a validated LC method, involving DMSO,1M HClO4, water as mobile phase and a C18 RP column maintained at 40°C. However, I'm observing a decrease of retention for the compounds of interest run after run. The decrease of the Rt of the main peak for example is about 1' at each run, leading finaly to loss of resolution. The phenomenon is observed using different columns. Any idea about this problem?
By Anonymous on Friday, March 5, 2004 - 03:09 am:
Silica based C18 columns could withstand such a low pH. May try a Zirconia or polymer based columns instead. BTW, check the validation report to see any decreasing RT.
By Bill on Friday, March 5, 2004 - 11:26 am:
Zirconia and Polymer columns resulted in a loss of resolution. And the low pH is needed to get a good separation.
In the report it is stated that the amount of DMSO is adapted in function of the age of the column. But the reduction of Rt run after run seems to be an unexpected result.
By Tom Mizukami on Friday, March 5, 2004 - 03:20 pm:
Something doesn't compute. You are using one molar perchloric acid with DMSO as the mobile phase? If this is accurate I wouldn't expect the column to last long because you will hydrolize the siloxane bond between the C18 and the silica. You are basically turning your C18 column into a silica column and will see exactly what you are seeing a progressive loss of retention and plate count.
By Andreas Neumaier on Monday, March 8, 2004 - 03:31 am:
The agilent (StableBound) SB-C18 is the only column I knew which could handle very low pH at higher temperature.
Maybe you should give column a try.