Chromatography Forum

We are looking at using the Restek EZ No-Vent System with our Agilent GC(6890N)-MS(5975B) so we do not need to vent the MS when changing columns. In the past we have used a microfluidic switch, but found that it greatly reduced the sensitivity, which was a problem for trace analyses of environmental contaminants.

Does anyone have experience with this system and have you found any major and/or recurring issues (e.g. decreased sensitivity). I have seen it mentioned somewhere that the ferrules get stuck in the EZ no-vent and it needs to be replaced regularly. Has anyone else experienced this?

Finally, our system uses EPC. Has anyone had any issues setting up the EZ no-vent with EPC software (which cannot compensate for the changes in flow) - or is this only an issue for software that uses retention time locking.

Thanks.

We tried one of those maybe 10 years ago and didn't have that much luck, but they could have changed the design since then.

If I need to change the column but not clean the source(mostly with the instruments used for Volatiles analysis) what I do it drop the source/quad temperatures by doing the vent cycle. Once the vent cycle completes I leave the rough pump running, remove the inlet of the old column and plug it with a septa, install the new column in the inlet and let it flush while I set the nut and ferrule on the outlet end with the tool, then quickly remove the old column and insert the new one with the carrier flowing and tighten it up. You only get a small amount of air sucked into the analyzer and with it still under vacuum and relatively warm it will pump down and heat back up very quickly.

It is not the recommended method, but when you have a ton of samples waiting and you have to be back up as quickly as possible it does work.

I have had some luck with the same approach James outlined. I assume it is still risky and only do it occasionally.

I have had some luck with the same approach James outlined. I assume it is still risky and only do it occasionally.

As long as the high vacuum turbo/diffusion pump is off and in vent mode it shouldn't damage those, just don't try it with them at full speed/hot.

Biggest problems would be oxidizing the source if the temperature is too high and the moisture that gets in, but it is way less than when bringing the system to atmospheric pressure.

Another shortcut that I was shown by an Agilent service engineer that I have only tried once was changing the rough pump oil while it is still running. As long as it doesn't go completely empty before you begin adding new oil it will maintain vacuum. The one time I tried it I let it drain too much and the instrument kicked over into vent mode, but came right back up once I put more oil in it. Mostly though I do a full vent when changing the rough pump oil because I run molecular sieve moisture traps on the lines before the pump and it is best to change out the molecular sieve each time I change the pump oil.

Thanks for the replies.

I was just wondering how you guage the length of column to insert through the GC-MS interface? There is very little wriggle room when installing the column at the interface (i.e. 1-2 mm of column protruding from the interface on the MS side) and tightening the interface nut could push the column through further and seems a little risky...

Cheers

Thanks for the replies.

I was just wondering how you guage the length of column to insert through the GC-MS interface? There is very little wriggle room when installing the column at the interface (i.e. 1-2 mm of column protruding from the interface on the MS side) and tightening the interface nut could push the column through further and seems a little risky...

Cheers

Normally the tool kit that comes with the Agilent 5973/5975s has a tool that looks like the inlet fitting with a long narrow tube attached that is the same length as the interface. You insert your column with the nut and ferrule attached, let it protrude from the other end of the tube, cut it off then slide it back so that it is even with end and mark your column at the nut. Slide it back a little and remove the nut from the measuring tool then insert into the interface and slide it up to the mark and tighten. It should not protrude more than about 1mm after it is tight.

I have seen some instruments, especially used ones, that do not come with the tool kit or it is missing the tool.

"Column installation tool (not supplied with the MSD)(G1099-20030) "

Just copied that from the 5973 manual online, seems they stopped shipping the tool with the instruments, but you should be able to order it with that part number. You can also just use the old portion of column as a measuring device, leave it in the old nut, have a second one for the new column then compare the new one to the old one, mark and you have your depth set.

Next time repeat using the first nut that has had the column and ferrule removed. You can use a simple push pin if you need to force out the old ferrule, and always use graphite/vespel ferrules not the graphite ones used for the inlet.

I use the Agilent quickswap system which is an auxilary gas fed insert that sweeps column effluent through a 100um restrictor through the transferline. The sample is diluted as the Quickswap aux gas flow is typical ~1.3ml/min and the column flow is 1.0 ml/min.

Getting that insert to form a seal on the transferline was a total nightmare for me. I haven't touched it in a year.

Agilent recommends using a two way splitter with makeup. I spoke with an Agilent apps person this week. They have a new flexible metal ferrule that replaces the siltites. I've never has an issue with the siltites connecting to the column or insert.

I use the quickswap a lot. I use a dedicated db5ms for 3-mcpd analysis in the back with the autosampler and on the front I switch between a general use db-5ms or Innowax column to support flavors dupplications typically manual SPME. I just hook up the rear column to the quick swap at night and let it go overnight and do the duplication samples during the day. Naturally I have to remove the innowax from the front if I was using it. and I just keep a flow on the front column if it is the gen use db-5ms.