Chromatography Forum

On our Agilent 1200 we are using 0.2 micron disposable precolumn filters (SECC)
Every time the rotor switches from mainpass to bypass it causes an increase in back pressure.
Therefore in a sequence each injection causes an increase in backpressure, so that when a large sequence is run, the system will eventually over pressurize and not be able to complete the sequence.

I am thinking some proteins are getting stuck on the instrument somewhere and the rotor change is causing them to be dislodged each time and being caught in the filter?

If this is the case, does anyone know of a recommended solution I can run through the system to clean it?

Or does anyone have a suggestion as to why this might be happening? I have cleaned the rotor, stator, and replaced the neadle seat, but the problem still persists.

Any help would be appreciated.

Does this still happen when you inject just water or solvent? I think you need to first isolate whether something is happening just from the valve switching or from your sample.

Does this still happen when you inject just water or solvent? I think you need to first isolate whether something is happening just from the valve switching or from your sample.

It even happens when NOTHING is injected. Just the valve switching from mainpass to bypass causes the increase. I have tested it just switching the valve back and forth and the pressure continues to increase.

Sounds like it could be an injection rotor seal issue. When have you replaced it, and cleaned the injector valve?

Sounds like it could be an injection rotor seal issue. When have you replaced it, and cleaned the injector valve?

A couple of months ago it was replaced. But I cleaned it ( sonicated and blew air through stator holes) and it still has the same problems....

The lifetime of the rotor is generally measured in the number of valve acuations which is proportional to the number of samples run. When running samples with high salt or other solid content the lifetime will be reduced.

I dont have any concrete information about the expected lifetime of the stator but my understanding is it lasts longer than the rotor.

Hopefully someone on this forum will share their knowledge of the stator material of construction and why it lasts longer than the rotor.

Another wearable part to remember is the sample metering pump seal. It too must be replaced periodically and since mobile is flowing through the pump head durng a run it can also contribute particlulates.

My experience with Rheodyne injectors is that parts coming off the rotor plugged the capillaries attached to the valve, especially the one going to the column (which was usually 0.1 mm inner diameter). As far as I remember this plugging/restriction always happened at the entrance of the capillaries only, not the exit. To cause the described restrictions of a frit/prefilter by particles from the rotor one would then either have to have larger capillaries or extremely fine rotor disintegration, which would have to be disseminative in either case. I therefore wonder whether the observation is really only connected to actuating the valve or whether it is really happening continuously due to critters (etc.) in the mobile phase.

Rheodynes have a rotor made of Tefzel or Vespel (I think, didn´t someone just state that somewhere?), while the stator is a ceramic, never changed one in more than 30 years.