Chromatography Forum

On an Agilent 6890/HP5973N with a 10m AT-1(100%dimethyl) .25mmID.

This column was installed 11/25. A conditioning program 40-350 with 45 minute holds at both ends and a 5 per min ramp was run six times before installing column. The column has run fine since installation. Today(12/2), the instrument was unable to reach starting pressure for our screen method(1 min @100-325(1 min hold) ramped at 50/min), so we changed the septum and swabbed out inj. port with MeOH. Did not solve problem. Pulled capillary adapter and cleaned gold seal at bottom of injection port and changed liner, this solved the pressure problem but the next run has massive column bleed that increases during the run. I thought perhaps a part of the column rested against the oven when the adapter was out so I cut about 1/3 of meter off the head of the column. Still has same problem. I'm stumped on this. Any ideas? I don't have a new column to put in. I have the old one, but it was starting to bleed a little before it was switched.

PS I know the method and column are not optimizing theoretical plates but this method has worked for several years on this instrument.

Syfir,

I hope I'm wrong but your column is probably dead. Is the bleed siloxane related?

If yes your pressure problem (i.e. air leak) has likely damaged the column on the entire lenght. The only thing you might do is to test the old one.

You are using quite a fast temperature gradient. After 2-3 runs you may have a leak at the detector side (if you use standard ferrules....). Maybe you need to consider/check that.

Regards.

bhuvfe

Yes, column is dead. We use vespel ferrules on the interface. Trying out the old one now to see if we can limp by with it until the new column comes in. The pressure problem was not a leak though. The inlet could not get low enough to start the method.