Clean your split vent line people!

[MSCHemist]

So for the first time I decided to take the split line off my 6890's main injector. I noticed some black gunk on the end so I dripped some MeCl2 down the line into a beaker and an insane amount of the most foul looking black and brown crud flowed out of the line. I was amazed all that crap even fit into the line. I cleaned out the injector and split port while I was at it.

I gave up trying to clean the line and just cut a nice new one off my GC copper spool.

Definitely have clean the split line on your maintenance schedule from now on.

[cleh]

Agree!!! It is often forgotten and gets very nasty!

[MSCHemist]

What I don't get is why it doesn't need to be replaced almost weekly. The line is unheated so of course everthing that gets split from the hot injection port will condense in the cool line and just stay there and build up.

[Yama001]

I would clean it monthly if you inject a lot of crap - its actually pretty easy on the 6890 - just disconnect at the filter end and rinse some solvent (I would use methanol as well) in - keep the end high enough and let gravity wash it into your inlet (column disconnected of course), then finish cleaning the inlet. Blow dry with whatever you have available (an empty squirt bottle will work in a pinch).

If it is clogged a syringe pushed through a septum can help block the filter holder and give you some pressure.

I agree it is odd that anything even gets through the line rather than just condensing at the split elbow. One of our people managed to clog his split elbow with glass splinters, so all manner of gunk built up.

[Forse]

I identify solvents in glue by GC, so my split line gets filled with the worst kinds of crap, often engineered to be solvent resistent.

My cleaning process involves heating the inlet to 300C while I try to poke a needle throu the vent opening from inside the liner chamber. I dont need to get it clean, I just want to get gas throu.

Right now one of my GC's is down due to a blocked pressure sensor line. (Perkin Elmer Autosystem XL)

[James_Ball]

I have found that when the split lines gets very dirty you can also get more breakdown when using splitless injections. Amazing how the analytes manage to travel up into the split area before coming back into the column but it does happen. If doing EPA 8270 semivolatiles and you begin to lose pentachlorophenol, sometimes cleaning the split line will fix it.

[Peter Apps]

Clogged vent lines are an inevitable consequence of back-pressure regulated inlets. With fancy pneumatics downstream of the inlet there has to be a split line filter to sieve out the crud, and it all has to be at room temp. When it was first introduced, back-pressure regulation was promoted as providing inlet pressures (and therefore retention times) that are robust to leaks at the inlet. This advantage applied particularly strongly to instruments which fed carrier gas to the inlet through long pieces of narrow bore tube, but if the upstream pressure regulator had a 1/8 inch connection to the inlet, then the inlet pressure stayed the same even with a leak. Leaks large enough to shift retentions will let in enough air to fail MS leak tests, and to damage columns.

Unless there is some major advantage to back-pressure regulation, going back to front-pressure regulation, with the split ratio and the septum purge set by simple needle valves in the inlet hot zone would be the most straightforward solution for clogged vent lines.

Peter

[Yama001]

That was an excellent explanation, Peter. I have always wondered about that, thanks.

[BMU_VMW]

I'm reading this topic with a lot of interest and I'm wondering if this problem will occur with a PTV-injector as well?

In our system there is a small filter between the PTV-split and the split-valve itself to prevent little glass beats from the liner to enter, and block the valve. This filter is not actively heated (but is on top of the GC so will get warmer during a GC-run) but when replacing the filter it never occured dirthy.

BMU

[Peter Apps]

If operated from below the solvent boiling point a PTV does not suffer from the pressure pulse that squirting solvent into a hot inlet produces, and so there is less chance of "raw" sample blowing up into the split line, which is what James Ball's results clearly point to. If I recall there have been other threads that lead to similar conclusions - the sample (even that part of it that ultimately ends up on the column) is going into some very strange places with flash vaporization injections.

What system do you have ?

Peter

[BMU_VMW]

We inject 50µl CH2Cl2 into a liner with sintered glass-beads at 50°C. This is slightly higher than the DM boiling point (40°C) but we are counting on the cooling effect of the DM evaporating in the liner.

BMU

[Peter Apps]

The higher than atmospheric pressure in the inlet will also increase the BP of the solvent. I think that there are some online calculators for this - try googling vapour volume caculator gas chromatography.

Peter

[MichaelVW]

How? :\

I have the care of a severely neglected Varian 3800 with (I think) a 1079 injector. We're still getting to know each other. It seems that the split vent outlet is permanently attached to the injector. If it's full of nastiness (and judging by the liner I just took out, it probably is) - is there any way to clean that? Or to do anything further downstream?

I think there is a blockage somewhere at any rate. Our service tech (who openly prays for this thing to just die) says the injector is a consumable that will have to be replaced if there is a clog. That's fine with me but I want to try cleaning stuff first.

The control panel on the instrument doesn't work (the display does but non of the buttons - this has been replaced numerous times). So I can't do much there to try and diagnose things. Should be getting the nth panel soon.

[MSCHemist]

Is it a case of brass/copper welded onto steel by corrosion? sometimes ammonia can help dissolve the salts.

Can you get either end of the line detached? If so drip some MeCl2 down the tube and through the injector.

[chromatographer1]

It has been a few years since I worked on a 1079 injector, but I think it is replaceable. And if replaceable, it can be removed, cleaned, and returned to service.

That would be my suggestion.

Rod