Chromatography Forum

Hello all!

I am encountering a problem with extremely high back pressure. I have isolated the cause of the high back pressure to the flowcell and believe there is a blockage somewhere in the tubing. Before I open up the flowcell, are there any washing/cleaning methods that work particularly well on a blocked flowcell? 1 cm analytical flowcell, Dionex U3000 HPLC.

Thanks in Advance

-mant0

Please consult your operating instructions. Page 103 for the VWD-3000 series, Page 86 for the PDA-3000. These pages descibe the different cleaning options.
Another recommendation: Reverse the flow direction (backflush the cell) and carefully increase the flow rate, so you remain below the maximum pressure rating of the flow cell.

A physical blockage in a flowcell is very unusual. For something (either particle or chemical compoun) to precipitate in the flow cell, first it has to travel through the injector, then the tubing before the column, through the column, through the tubing after the column, and then suddenly stop in the flow cell. I do not believe this happens very often, but if it does, you may have some serious method problems that should be fixed.

There are two other possible explanations:
1. If your compound is photosensitive, the low wavelength UV light from a diode array detector could cause polymerization, which might precipitate in the flow cell. But this would take many injections, since you are injecting ng each time.
2. The tubing that is connected to the flow cell may be bent. PEEK tubing can develop very high back pressures if it has a "kink." Stainless steel tubing can sometimes show the same problem.

Thanks hfranz and mbicking for your responses.

I have tried the cleaning with 50% MeOH as suggested in the manual (have not tried the nitric acid) as well as backflowing at 0.05-0.1 ml/min. At these flowrates pumping 50% MeOH, my backpressure is high at around 20 bar. Neither of these approaches have lowered the backpressure unforutunately.

The connecting tubing to the flow cell is PEEK, however, after taking apart the inlet and outlet tubing and running solvent through them, the pressure for both the inlet and outlet tubing is normal. I'm really curious to how a blockage could have occurred. (Also, i have been injecting ug of sample)

Thank you,

-mant0

What is the normal flow resistance of your cell?
Remember: these resistances in series are additive, so your 20 bar will just add to the other back pressures at the same flow rate.