By nopcbs on Monday, May 3, 2004 - 09:05 pm:
Consider:
Agilent 1100 series LC with autosampler, binary (or quat) pump, degasser, UV detector @ 260 nm.
Gradient separation going from a hexafluorisopropanol/diethylamine/EDTA/pH 7.4 mix to 95/5 EtOH/isopropanol.
Kromasil c18 column (good to pH 9.4)
50 C operating T.
With some batches of eluent, and no injection made, there is a large peak observed about 1/3 of the way through the gradient program. Sometimes it happens and sometimes it does not on several 1100 systems.
On some systems, the peak only occurs after the system has been standing for a day or two unused, but not once the system is running regularly.
One individual thinks it is a result of EDTA complexation with iron or Cr or Ni (or other minor metal species) from the 316 SS of the system. The idea is that the complex is retained on the column until the gradient pulls it off.
Problem with that is the great lack of reproducibility we see.
Anyone observe anything like this with EDTA as modifier?
By Andreas Neumaier on Tuesday, May 4, 2004 - 08:01 am:
Do you purge the degasser before running the gradient? I guess the degasser is running all the time and your solvent partly evaporates.
By Chris Pohl on Friday, May 7, 2004 - 05:25 pm:
It is definitely possible that the EDTA is causing the problem. You might want to try rinsing the system to remove EDTA from the flowpath before shutdown. By the way, be careful with the hexafluorisopropanol. It's quite dangerous and can cause clouding of the cornea!