MSD 5975 Tune Problems

[MSCHemist]

It could also be coming from any of the connections in your vacuum system including where the foreline pump hose connects to the foreline pump, the vacuum/turbo pump, the gasket where the turbo/diff pump attaches to the main body etc,

[Absolutdude]

I checked the PFTBA valve, but no change if I close the valve. So no leak there.

Anyway, the O2 is at 1,12%, N2= 2,75%, H2O=5,56%.

So I think this is maybe not to bad and would go back to work. What do you think?

With two columns and and a Y-Splitter there a plenty opportunities for minor leaks (even though I didn't change anything at the second column or the y-splitter)
But as I said the values for O2, N2 and Water were always a bit high since I work here.

If I will get my Argon, I will go on the hunt to see were the leak is...

[tlahren]

I would say those values look fine to start working again. I would keep a close eye on them however. Like you said, considering all the extra connections you have, there is probably bound to be some small additive leaks in a variety of places.

Good luck.

[Bigbear]

Doubt it is an air leak. If it's air the N2 should be about 4X the O2. Maybe it needs more pumping out time. Have you baked out the MS? Should be a bakeout macro in your software.

[Bigbear]

A Y spliter and 2 columns! What is the total gas flow into the MS? Too high a gas flow can cause tuning issues. I'm remembering that somewhere about 2cc/min is the maximum flow for a 73/75.

[Absolutdude]

...thanks for the info.
The total flow to the MS is 4 ml/min. I heard this is the flow the technical service advised us...

After the tunings over the last few days (did not had any runs on the GC/MS) the O2 droped to about 0,5%; N2=2%. So I felt really good about it.

After I did some runs yesterday, the 02 increased to 2% and N2 to 5%. So I think this is an indicator that I have a minor leak somewhere in the GC.

[tlahren]

After I did some runs yesterday, the 02 increased to 2% and N2 to 5%. So I think this is an indicator that I have a minor leak somewhere in the GC.

What kind of splitter is it? The SilTite ferrule based splitters are virtually leak free if you install them correctly. And they are easy to install. The glass Y-splitters have problems often.

I have run 4 mL/min in the past without any noticeable problems. I wouldn't suggest going any higher than this though. Is is possible to reduce the flow of the column you are not using? I'm assuming to get 4 mL/min total flow to MS you are running two inlets to the one MS interface correct? When you aren't using the other injector I would set the flow (for that method) to a low 1 or 2 psi constant pressure. This keeps the total flow to the MS down and prevents your analytes from sneaking up the other column.

[Absolutdude]

It is not a glas Splitter. I don't know the exact name but it is one of the Agilent’s Capillary Flow Technology Splitters.

Yes, it is possible to reduce the flow on the column I am not using.
And yes you are right. Two inlets are going to one MS. Total flow through the MS interface is 4 ml/min.

I will trie to set the pressure (of unused injektor) down. Do you think a lower flow to the MS could increase the sensitivity?

[tlahren]

Yeah that sounds good. I think the Agilent splitters are actually made by SGE. Not sure but I do know that SGE makes the Ultimate Union and Purge Unions for Agilent. If you installed it per the instructions I'm fairly certain you won't have any considerable leaks at this splitter.

Well, theoretically a better vacuum (i.e., lower He flow through the MS) should give you better sensitivity (more ions making it to the detector anyway) but I have not done a comparison of sensitivity from 1 mL/min to 4 mL/min. I have generally not had any problems with sensitivity at higher flow rates. However, you will notice a considerable increase in vacuum when you lower the total flow. Flow reduction may help tuning as well.

[MSCHemist]

Do you have an insert that screws on to the transferline with a capillary with siltite ferrule that the insert compresses against. I have the quickswap system and trying to get a seal on the transferline was a nigtmare. Agilent finally sent us another insert and I had to put oven mits on and crank that sucker down to make it stop leaking. I am not touching that thing ever again just leave it on.

The stiltite column connection gives me no issues though it is very easy and reliable to take off an put on again.

[BCBC]

MSCHemist,
You had a magnet replaced?

[MSCHemist]

Yep I was preparing for possible H2 conversion. At the seminar they mentioned some older 5975's had magnets that didn't work with H2 If your magnet just says S and N and has no serial number it should be replaced.

An Agilent Service engineer did mine for free but I could have done it myself. You vent the system, take the source out and the Magnet is C shaped and the section above the N is held on only with magnetic attraction and it pulls right off and goes right back on.

[Yama001]

That is interesting. My understanding is the magnet enhances ionization by inducing a 'twirl' in the electron beam, allowing for more interaction with the eluting molecules. I would guess a different magnet for hydrogen carrier is related to ionization issues?

[tlahren]

That is interesting. My understanding is the magnet enhances ionization by inducing a 'twirl' in the electron beam, allowing for more interaction with the eluting molecules. I would guess a different magnet for hydrogen carrier is related to ionization issues?

My understanding is that is had more to do with corrosion issues as using H2 can lead to corrosion of MS parts.

[MSCHemist]

especially if you inject a lot of chlorinated compounds as it can form HCl gas.