Chromatography Forum

Hi @ all,

we have some trouble with a high water and air content in our system. We did a leak check with Argon and 1,1,1,2-Tetrafluoroethane but there is no leak detectable. Our water content today was around 20%. The same for Nitrogen. We are using a special software for our system and not the Chemstation. One problem is that our pressure gauge seems to be broken because the values sometimes jump from 5x10^-6 to 3x10^-3 Torr in Milliseconds. Now we have a flow of 2.8mL/min and a pressure of 1.16x10^-5 Torr (The Agilent Guide says it should be at least 1.86x10^-5 Torr). If we can trust the pressure gauge this value would be ok.

Picture 1 shows the abundances from last Friday. The system is only flushed with Helium as carrier gas. So shouldn't Helium have the highest Abundance if we don't find any leak? Because Nitrogen and Oxygen are much higher.
1)


Picture 2 shows the abundances from today. Yesterday we putted the gas bottle out of our gas bottle cabinet to connect it with a 2m long tubing directly to the GC and heated it out over night (we thought that the Air/Water might come from the lines in the wall). When tho oven was opened the water signal became some oscillations.
2)


Picture 3 shows the tuning results from the last days. The air-water parameters on Friday 151127 1456 seemed good. The tuning parameters before changing was 151130 0800. Actually we increased the system temperatures (MS source 230°C, quad 210°C, oven 200°C and interface 200°C, the default temperatures before the run were MS source 150°C, quad 130°C, oven 40°C and interface 200°C) to clean the system overnight. But the air-water parameters seemed bad when we did the tuning test this morning and we didn't detected any leak.
3)


All in all we have these poor results since we cleaned the source and exchanged both filaments but we are quite sure that we did everything correct.
We hope that anyone can give us some hints and help us. Thank you very much.
The Medusa-Team

If the air and water increased only after cleaning the source, it could be that the side plate seal is leaking. Even a tiny piece of lint or a hair across the o-ring can cause a leak like this. Also sometimes the side plate will have trouble seating flat against the o-ring and you have to hold pressure on it as the vacuum is turned on.

I have had to use a light film of Apezion L grease to coat the o-ring to get a complete seal if the instrument is older. It will not contaminate the instrument and will help seal any microscopic cracks in the o-ring.

Also, did you change the ferrule on the column interface when you cleaned the source? Those can shrink over the first couple days after changing and cause small leaks also, you just have to turn the nut about 1/8 turn to reseal it if it does.

Hi James,

thank you for your reply. We are quite sure that the interface nut is tightened because we did a leak check with Argon and 1,1,1,2-Tetrafluoroethane and there was no peak for these masses.

We did the same with the side plate and didn't get any peak. One possibility what we're thinking of is the back part of the side plate/ seal because if some Argon or 1,1,1,2-Tetrafluoroethane could go in there its directly sucked away by the turbopump and not getting into the source and ionized.

Another possibility is we're using an old He pressure regulator at the gas bottle because we putted it directly next to the gcms to do some tests. This pressure regulator wasn't used for a long time. With snoop and a He leak detector we didn't find any leak at the pressure regulator or the tubing. Do you think that this could also be a reason for the high water content?

We only have Apiezon N grease and reopen the ms chamber today and put a new light film on it. We hope that this will help.

Hi James,

thank you for your reply. We are quite sure that the interface nut is tightened because we did a leak check with Argon and 1,1,1,2-Tetrafluoroethane and there was no peak for these masses.

We did the same with the side plate and didn't get any peak. One possibility what we're thinking of is the back part of the side plate/ seal because if some Argon or 1,1,1,2-Tetrafluoroethane could go in there its directly sucked away by the turbopump and not getting into the source and ionized.

Another possibility is we're using an old He pressure regulator at the gas bottle because we putted it directly next to the gcms to do some tests. This pressure regulator wasn't used for a long time. With snoop and a He leak detector we didn't find any leak at the pressure regulator or the tubing. Do you think that this could also be a reason for the high water content?

We only have Apiezon N grease and reopen the ms chamber today and put a new light film on it. We hope that this will help.

Another place I have checked and also had to tighten is the end plates on the analyzer chamber. The four torx bolts on each end of the analyzer, you can get a leak there sometimes. Another place that is difficult to find a leak is where the interface attaches to the analyzer because it is covered with the aluminum cup and insulation that goes into the GC oven. The washer there can leak sometimes too.

If it was the old regulator, you should be able to disconnect the line and let it flush at high flow for a few minutes and get it to go away.

Hi James,

Thank you for your advice.

We putted the Helium cylinder back to the gas bottle cabinet yesterday. Today we detected a leak from the Union connecting main column and deactivated column. We changed it to a new one. No leak from the Union now.

Another question is water abundance went like a wave after we injected argon near the interface nut at 120s (see Picture 2). Do you think the unstable water abundance after 400s is still influenced by the temperature variance of interface nut?