Chromatography Forum

Hi,
I running a HP 6890 with a 5973msd for epa 8270 analysis. I'm having a problem with the gc shutting down because it is unable to achieve or maintain the pressure set point. I'm running a pulsed splitless injection with the pulsed pressure at 15psi backing down to 7.4psi. At times the inlet is able to able to achieve the pulsed pressure but when backing down is unable to maintain the 7.4 psi set point until the gc shuts itself down. I tried increasing to total flow to 55ml/min and increasing the pressure at the He tank to 90psi which worked for a few runs but the problem returned after a day. I have leaked checked the inlet and column fittings and have replaced all o rings and the septa and have found no leaks with the leak detector. I'm starting to think that the epc may be the problem. Thoughts?

Re-check for leaks both at inlet and at the inlet fittings inside the GC.

When is the last time the traps in the split line were changed?

Are you using the Agilent "Gas Saver" option or not?

Definitely a GC issue, not an MS issue.

Is the pressure failing to drop to the 7.4 psi setpoint (i.e. staying high ?) or is it below the 7.4 psi setpoint ?, or fluctuatiing ?

Do you have flow out through the split vent, and is it fluctuating ? What about the septum purge ?

Peter

if you can check the split flow please check. i faced many time this problem and found the split valve of EPC is not working properly. agilent engineers showing the EPC problem but you can replace only split valve of EPC.

I have switched off the gas saver option as part of the troubleshooting process. It has stayed off with the problems persisting. I don't believe that the traps have been changed recently.

The pressure is not reaching the set point (too low) it is in the 6 psi range might be able to get up to 6.9-7.0 before shutting down. I'll check the flows when I get in to the lab today.

Thanks

It is very strange that it can reach 15 psi during the pressure pulse, but not 7.5 psi, or am I misinterpreting your first post.

Peter

Peter, that was correct in what I was seeing. The problem ended up being a o-ring degrading between the EPC and the purge carrier line and getting into the interface. I cleaned the bits of o-ring out and the gc seems to be holding at the correct set point. I'm running a bake out method tonight to see if this holds.

Peter, that was correct in what I was seeing. The problem ended up being a o-ring degrading between the EPC and the purge carrier line and getting into the interface. I cleaned the bits of o-ring out and the gc seems to be holding at the correct set point. I'm running a bake out method tonight to see if this holds.

Was it causing a leak or a blockage ?

Peter