Dear all members,
Recently I try to install a column of dimension 0.15mm x 25m x 0.12um in the Agilent GC 6890-5973 MSD and try to build up a column head pressure of about 30psi (equivlent to about 0.7ml/min). However, when I configure my GC to the above column dimensions, the column head pressure cannot build up to that value fast enough that the instrument goes to "safety shutdown". When I change it to 0.25mm x 25m, the column pressure can reach such value. I know that the column head pressure in the GC should be independent on the column dimension. The dimensions are only used for calculation of the linear velocity and column flow. Is there any limitation or restraints that Agilent initially set up in the GC so that I cannot use minibore column? Would someone has similar experience that could share with me?
By Anonymous on Tuesday, December 3, 2002 - 06:47 am:
I'd first check to make sure that you don't have an inlet leak; are you using the same ferrules for both columns, likely you need a smaller ferrule for the 0.15mm column unless you're using 100% graphite ferrule. Here we use 0.20mm columns everyday in a 5890/5971 and 6890/5972, both with EPC.
By Uberto on Tuesday, December 3, 2002 - 04:36 pm:
Thanks for your advice. I did check the inlet leak and it didn't show up any problem. Also I guess I didn't make it clear. I install a column of 0.15mm i.d. x 25m to the GC and configure the GC as is the dimension of the column and find that the column head pressure could not build up to, say 30psi fast enough that the instrument automatically shut down. However, when I configure or "cheat" the GC to the column dimension of 0.25mm i.d x 25m, the column head pressure increased normally to 30psi without instrument shutdown. I really don't know why. Could someone has similar experience?
By Anonymous on Wednesday, December 4, 2002 - 12:58 pm:
I sometimes experience this problem even with columns of 0.32 mm. What I do is increase the split ratio temporarily until the head pressure reaches the desired level. When I reduce the split ratio back to normal the pressure is usually maintained.
By Uberto on Wednesday, December 4, 2002 - 04:31 pm:
Thank you very much for your advice. Yeap, you are pretty right. I increase the split flow, i.e. the total flow of the column. The column head pressure increases to set value normally.
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