By Anonymous on Thursday, October 9, 2003 - 09:08 am:
Hi all!
I am using a Dionex Summit HPLC System and seem to experience high back pressure problems!
My mobile phase is composed of 0.025M KH2PO4 pH3 Buffer:Acetonitrile 90:10 and I am using a Genesis Phenyl 120 4ĩ 150x4.6mm with a 1 ml flow rate. I started with a pressure of 65 bars which is reasonable but overnight it rose up to 140 bars. Now, when the samples are injected the pressure drops to 100 and rise again to 140.
I did use a brand new column which I was conditionned with 60% Acetonitrile and 40% H2O. I prepared a fresh mobile phase as usual.
After my run I flushed the column with H2o for 10 minutes then with 60% Acetonitrile and 40 % H2O for 30 minutes and the pressure was still high. I do not understand. It is not a plugged frit as the column was used as new unless there is some precipitation somewhere?
It never happens usually.
Help please!
Thanks.
By HW Mueller on Thursday, October 9, 2003 - 11:57 pm:
Can your column be run backwards? If yes, what is the pressure, forwards, after running the column in reverse? Why are you so much worried about a backpressure of 140 bar? Donīt you use a pre-frit or guard column? The starting 65 bars... was that before the column was equilibrated?
By mbg on Friday, October 10, 2003 - 11:30 am:
Assuming the 65bar was after the column was equilibrated...
The plug may be in the capillaries before the column or the injector loop/system. A clue to this is the pressure drop as the sample is loaded.
Remove the column and see if the pressure drops to less than 10bar (pressure will vary depending on your system set up). If pressure is significantly high w/o column, isolate the plugged part and replace (or sometimes tubing can be unplugged by reversing it and washing the particulate out).
Last time I had this problem in my Agilent 1100, it was the autosampler syringe that was plugged. Replacing it cured the problem.
Should this not be the problem, I suggest contacting the HPLC manufacturer tech support to assist.
By Anonymous on Monday, October 13, 2003 - 03:03 am:
just change the column and check either problem in column or in the instrument
By SA on Wednesday, October 15, 2003 - 01:02 am:
If you wanna be sure where the problem comes from, you may open column end connection and watch if is there any changing on the pressure. When column is plugged, pressure shouldn't change i guess.In my opinion there is a plugged part in your HPLC system.Some systems have inlet filters apart from solvent filters. Also you may check solvent filters. Another thing if pressure rises up during or after injection, you can check sample solvent. Maybe it's too viscos or there is a immisciblity problem between your mobile phase and sample solution.
By Anonymous on Wednesday, October 15, 2003 - 04:55 am:
Does the pressure drop to 100 bars during the injection sequence, or only when the valve cycles to actually inject the sample? The reason I ask, is that the sample loop is taken out of the flow path during the injection cycle and then is put back in the flow path to actually inject. If your pressure drops when the loop is taken out of the path, then there is probably a blockage in the loop itself.