Chromatography Forum

I have an old 5890 II GC attached to 5972 MS. The instrument has been working and tuning fine. However, since couple of days ago the pressure gauge shows 0 (helium pressure). This usually happens when the helium is low, or during inlet maintenance. the helium is definitely not low and I couldn't detect any leaks. Samples are running as usual meaning there is sufficient helium flow. Turning the knobs (column head pressure, split, etc.) makes no difference. Is it possible that the gauge just stopped working?

That is really strange. If you adjust the split flow, you should see more or less of your sample. If you adjust the pressure, you should see a retention time shift,. This will sound crazy, but do you have two injectors on the GC? If so, is it possible that the gauge reading zero is for the injector you're not using? Just a thought.

I'd confirm the zero pressure using a needle pressure gauge inserted into the septum. Measure flow at the split vent and septum vent too.

I'm thinking you have a leak and just can't find it. Make sure the stainless steel nut under the inlet (accessible from the column oven compartment is tight, and that the ferrule on it is not leaking.

Also, what about leakage at the gold seal inside that nut? Are you using the traditional type with the thin sealing washer or the newer ones with vespel ring?

Samples are running as usual meaning there is sufficient helium flow. Turning the knobs (column head pressure, split, etc.) makes no difference. Is it possible that the gauge just stopped working?

If the retention times are not shifted then you still have the same head pressure as before. Sounds like the gauge has stopped working. I have had a few that got to the point you had to tap them gently with the handle of a screwdriver to make them read pressure after doing maintenance. The gauges are mechanical so they will wear eventually and on a 5890II it is at least 15 years old if original so it could simply be that it needs to be replaced.

Until you can replace it you will have to set the split and septum purge flows where you want them then adjust the head pressure until you get the correct retention time which you had previously, then do a final adjustment on the purge flows and that will get you back to where you were before.

could it be a problem with the electronics that control the EPC?