Front Inlet Flow Shutdown on HP 6890 MSD 5973

[Oliver007]

We currently have a GC-MS 6890-5973 that we are using in our studies. I did some routine maintenance on it yesterday, changing the septum, inlet liner, and UHP He tank. After re-equilibrating the system, some experiments were run using an HP-5 column. We are constantly getting an error reading when the oven temp reaches about 270 degrees C (the max. allowable temp. is 280). This error is a front inlet flow shutdown error, and it is occurring, I think, because the front inlet pressure is becoming too high. The default, i.e. standard, setpoint inlet pressure for the experimental runs is 7.6. Near the end of the runs when the instrument shuts down, it has increased all the way to 19+. I can prevent this shutdown from happening by merely starting the run at a lower pressure (such as 6.0), but I've never experienced this problem before and I don't understand why it is happening. I tried changing the septum and inlet liner again, thinking that they perhaps may be faulty, but this did not help.

If anyone else has experienced this problem or knows what could be the problem, I would greatly appreciate your help, advice, or input. Thank-you in advance your time!

[Consumer Products Guy]

I think you need to supply more information. First of all, sounds like a GC issue, not affected by the MS. If you're running constant pressure mode, the pressure should stay the same throughout with your EPC.

If you're running constant flow mode where the pressure increases with higher temperatures to keep the carrier flow constant, the my guess is that the issue is a small leak, and your EPC can't keep up to the designated pressure required, so it shuts down. Since you just worked with the inlet, I'd re-tighten the inlet bottom a little so the O-ring is compressed further, maybe use a new O-ring. Make sure the septum nut is tight as well, and maybe your septum is leaking a little due to piercing it.

[chhubert]

Front inlet pressure shutdown does happen when the preset column head pressure cannot be reached due to some reasons, in most case, system leaking. Also when you set the EPC in constant flow mode, column head pressure will increase when oven temperature increases to compensate the drop of flow rate due to the increase in carrier gas viscosity. I suggest you'd check whether everything is tightened to prevent gas leak, say the septum, o-ring inside the liner, and inlet ferrule connecting the capillary column. Also do not tighten the septum nut too much, finger-tight is enough, or leak may happen after it's pierced by syringe needle.

[Peter Apps]

Assuming that you have checked for leaks (using a leak seeker, not just by tightening every nut) there are a couple of other potential causes.

On the method screen, check that the column outlet is selected to MS vacuum.

Set the linear flow rate not the pressure, and use constant flow mode.

You can select inlet pressure as a data output, and plot out the results at the end of the run to see when the pressure rises.

Check that the gas saver flow and the split flow are not too high - 20 ml/min is plenty for gas saver.

Check that the pressure in you helium feed lines is high enough (3 bar or so at least).

Good luck

Peter

[Rick]

You have change your He tank...have you change the pressure of your tank exit?
If not, suspect inlet leak or column leak at the injector, or maybe, He tank don't contains He....label error!!!