water level in GCMS

[kabavik]

Dears,

I am working with Varian 3800:4000 GCMS.
I have problem with high /elevated level of water. Water cant be removed even during few bakeout.
Helium is utraclean, external filter (oxygen/moisture) is new and dont indicate saturation.
Vacum in MS is below 10uTorr showing leakless sytem,
additionaly,
when i disconnected MS from GC, water was removed which show that problem is coming fromGC.

Water cant be removed it is mean that is still supply, but if Helium is clean where can be source of water?

Ill be appreciate for any suggestions.

regards

kabavik

[Yama001]

I had an Agilent 5972 that had elevated water background for months. It eventually went away; I suspect we had left it pumping over night with the column disconnected from the inlet, perhaps gettting a lot of water into the rough and diffusion pump oils. We lived with ours but perhaps changing the pump oils is worth a try. Since you capped off the MS it is likely not the problem, but sometimes the lower vacuum in a capped off MS produces unusual results.

Note also that certain types of tunes can really elevate the water and air background.

Tim

[dim56625]

Hi Kabavik,
since you have already confirm that the problem is coming to the MS you have to check all the connections for leaks. Replace the septa, close the injector nut, check the connections in the oven (column-injector, column-transferline). Condition your column for a few hours by keeping it a bit lower that its maximum temperature limit. Check the He line for leaks.

Good luck
Dimitris

[Peter Apps]

If the water is due to a leak from atmosphere then you will see high oxygen and nitrogen levels also.

Peter

[kabavik]

Hi

Thanks for all,

i had service of pump two days ago, and directly after, bakeout didnt remove water.
yestarday i removed inlet GC filter, which can be source of water if it is saturated => however after 4h of bakeout water was still high.
Next i changed liner, septum, oring in injector, increase temp of column to 120C and didi bakeout during 10h.
this morning is ok.

I cant recognize which factor finally helped, and i'll see it will be permament or trouble of water will come back.

Anyway, Peter, result of water / air check show acceptable level of air and high level of water. It didint change after few bakeouts.
If the source is not atmosphere leakn what it can be ?

[Peter Apps]

The water was very likely to be desorbing from surfaces somewhere in the GC, or from the column stationary phase. It takes a long time to remove water from any system once it has been contaminated.

Another possibility is that the "water" peak that you are monitoring is actually a fragment of something else.

Peter

[kabavik]

Just after 10H of bakeout -ok for air and water.

I analysed blanc test -Helium (and situation from few days repeated).
After blanc analysis again air acceptable, water high level (high intensivity for ions 14,15,18,19,28,32)

[carls]

When you state yopu performed a bake out do you mean an MSD bakeout (with our without GC column installed?) or a GC column bakeout?

ions 18 (H2O), 28 (N2) and 32 (O2) indicate a leak.

Perhaps you have water in your helium. Compressed gas manufacturers have production problems too, especially in conditioning and cleaning cylinders, so maybe you got a bad cylinder? Have you tried replacing the cylinder with one from another manufacturer? Is the water trap on your system an indicating type? If so, does it look OK? It may be worth replacing the water trap just to rule this out. It may take a day or so for the water to come down if your gas lines have been contaminated.

[kabavik]

Hi Carl,

Bakeout was done last night with installed column, which temp was increased to 120C, to remove eventually water from column.

Helium Alphagas 2 from AirLiquid always had good properties, additionaly i use external Gas cleaner with indicator, which doesnt show saturation, so I exclude fault of helium.

I checked all lines, connections in GC and i cant find any leak.

I have some idea but i'm not sure is it right.

I indicated water after blanc analysis when i heat column very high.
So i switch on heating of oven to 280C, and then i observed very high incease of water level.

Is it possible that internal filter in GC was saturated, due to this water gone to column, and is partially removed ?

I switch on regeneration of column.

[Peter Apps]

What kind of column do you have in the GC ?

Peter

[kabavik]

capilary column Porabond Q 25x0.25 0.3

[Peter Apps]

capilary column Porabond Q 25x0.25 0.3

Which my friend Mr Google tells me is a PLOT porous polymer with an upper temperature limit of 320C. Could easily be that it has a high affinity for water and that the 120C you have been using to bake it out is uneccessarily low. Check with the tech sheet that came with the column, or the manufacturer's website.

Peter

[nvalentine]

Agree with Peter. PLOT columns are notorious for soaking up water, but they can be regenerated run to run normally or through an extended bakeout if you saturate them.

I would also use care in using a PLOT column in an MS for fear of particles dislodging under vacuum. I think it depends on column ID on whether you can use them for MS, but you can also employ a guard column to catch any particles.

[carls]

A column "bakeout" is usually performed near the isothermal max of a column which is 300C in this case.

I dont quite follow your problem description.

What do you mean by a blank injection? No injection?

How is a sample injected? Syringe, valve with loop, etc?

What is the temperature program you used for the blank run? Is this the same program used for your analysis?

After allowing the column to sit in the oven at 120C for 10h the water signal is gone but after ONE blank analysis the water is back?

How high is the water relative to the m/z 69 peak? What %water does the MS report when the water is high?

[kabavik]

column "bakeout" is usually performed near the isothermal max of a column which is 300C in this case.

yes you are right of course, I did 4h of column regeneration at 280C, still water is not removed completely, then 3h additionally were switch on

I dont quite follow your problem description.

What do you mean by a blank injection? No injection?

blanck i mean injection of helium

How is a sample injected? Syringe, valve with loop, etc?

by valve with loop, additionaly instrument is equiped in sample preconcetration trap

What is the temperature program you used for the blank run? Is this the same program used for your analysis?

conditions for blanc are the same like for analysis: I use SPT and temp programme for column

After allowing the column to sit in the oven at 120C for 10h the water signal is gone but after ONE blank analysis the water is back?
exactly

How high is the water relative to the m/z 69 peak? What %water does the MS report when the water is high?

mass 19/18 ratio was about 120% after blanc
about 300% during bakeout of column
about 40% after 4h of bakeout