Chromatography Forum

6890/5973/purge&trap.

Today I cleaned the source and changed my vacuum pump oil. I haven't done a source cleaning on this particular instrument again so I ran an air & water check beforehand to get some idea of what to expect after I put the source back in. Did that, gave it a couple hours to pump down and did an air & water check.

Before:
mass 69 abundance = 543488
%water = 6.56
%nitrogen = 5.27
%oxygen = 1.28
%CO2 = 2.82

After:
mass 69 abundance = 620224
%water = 120.27
%nitrogen = 8.40
%oxygen = 2.23
%CO2 = 27.12

Maybe it just needs to pump more overnight - I'll see what it looks like in the morning. But I'm not used to seeing this on my other instruments... if I have a leak, Nitrogen is huge. I've never seen water over 10%. Any thoughts?

Hello

You have huge air leaks and water in the system.

1.Make sure that there is no leak between column and transfer line (MSD Interface) - the most common place for leaking. I'd change column nut.
2.Make sure that you have carrier gas trap in good condition (perhaps it is saturated) - replace if necessary.
3.Bake out MSD (there is function in drop down menu in chemstation) - if not: ion source 300deg, Quad 200deg and leave it for 3-5 hours.
4.Perform autotune and check air and water content

Regards

Tomasz Kubowicz

If there was a large air leak the nitrogen and oxygen would be higher than they are.

Depending on ambient humidity the surfaces inside the MS can pick up a lot of water while it is opened up, and it will take a lot longer than 2 hours to pump it out. A bakeout will help.

Peter

As Peter mentioned,
the adsorption of water onto the surfaces contributes to the water background.

A trick I use, is to keep the side plate closed, and to put the source in a GC oven @ 100'C for 30 minutes after I clean it.

A discussion with a Agilent Service engineer queried if the source gets oxidised at that
temperature, I replied that I never had any issues after doing this.

The only time I had an issue was when I reassembled the source and it wouldn't tune,
I disassembled it, and found a strand of my hair was lying across the entrance lens orifice.

Alex

Thanks everyone.

While I'm asking, does anyone have an opinion on solvents and rinse steps to use when cleaning a source? I use an aluminum oxide paste. The document I have been following has you make it with water, then do water -> MeOH -> Acetone -> Hexane sonications on the cleaned parts. But I've seen other places suggest using MeOH to make your paste, or use different solvents, or use them in a different order. Any pros or cons to doing it one way over another?

Thanks everyone.

While I'm asking, does anyone have an opinion on solvents and rinse steps to use when cleaning a source? I use an aluminum oxide paste. The document I have been following has you make it with water, then do water -> MeOH -> Acetone -> Hexane sonications on the cleaned parts. But I've seen other places suggest using MeOH to make your paste, or use different solvents, or use them in a different order. Any pros or cons to doing it one way over another?

As Peter mentioned,
the adsorption of water onto the surfaces contributes to the water background.

A trick I use, is to keep the side plate closed, and to put the source in a GC oven @ 100'C for 30 minutes after I clean it.

A discussion with a Agilent Service engineer queried if the source gets oxidised at that
temperature, I replied that I never had any issues after doing this.

The only time I had an issue was when I reassembled the source and it wouldn't tune,
I disassembled it, and found a strand of my hair was lying across the entrance lens orifice.

Alex

I do a similar process when cleaning the source. Keep the side plate closed except when removing and installing the source helps a lot.

If I am running semi-volatiles I sonicate the metal parts last in Methylene Chloride then bake at 50C for a few minutes and have very little water after pump down. If I am cleaning the Volatiles/Purge and Trap instrument I do my final sonication of the metal parts in Methanol before reassembly and bake at 50C for about 15-20 minutes, cool and put it back together. If you sonicate the metal parts in water last, it will take days to get it all out. Also never put any of the insulators into solvent or water because they will take forever to bake out.

(I kinda miss the insulators back on the 5970, you could bake those out in a muffle furnace at 500c and never have much water to worry about.)

As for the aluminum oxide solution, I use Citranox to make the paste, it works better than water or methanol. When you use water or methanol the aluminum oxide tends to just settle to the bottom and not stick to the swab well. It was an Agilent engineer who got me to using Citranox and it works really well. After cleaning I wash with hot water, then sonicate with a Critanox solution in hot water to shake loose any remaining aluminum oxide, then sonicate in water, then methanol. I do a final in Methylene Chloride if it is not being used for volatiles. I don't use that for volatiles so I don't have to wait for it to be vacuumed out, since it is a target compound and I don't want to have a high background for those ions.