Chromatography Forum

Hi all,

I had a serious trouble with my autosampler 2777C coupled to a Xevo-TQ. The system works as usually but during the injection step, I have a peak of the pressure (about 3000 PSI without column during 0.4 min).

I targeted the origin of this trouble and it is only in the injection valve during the switch. When I switch and let the valve in injection mode I maintain this overpressure.
I had washed (overnight and in injection mode) the system with several organics solvent. The pressure decrease but at each injection, I observe the same phenomena, a peak of pressure ..
If someone has any idea that could help me, it will be very nice, because I have no more solutions ..

Thanks!

If you are seeing the excessive pressure whenever the valve is in the "inject" position, that points to a partial blockage in the sample loop. I don't know if that system uses an external or an internal loop.

If it's external, the easiest fix is to replace the loop. If that doesn't fix the problem, you can try backflushing the valve (disconnect the pump and the column line and temporarily connect the pump where the column used to be.

If it's an internal loop, then your only option is to backflush.

If all the above fail, the valve will have to be rebuilt or replaced.