Chromatography Forum

Hi people!

I work at a GC6890/MSD5973 (with a turbo pump and cuadrupole).
I have a recurrent situation.
I must change the column once per month. And every time I have the same problem: the autotune don't finish ("cannot achieve constant peak widths") or that is horrible (a lot of peaks in the mass spec, deformed peaks of PFTBA ions). Always I finish of the same way: cleaning the ion source.

When I remove the column I put a septum in the ends. And then I install the other column, by conditioning to max temperature for 1-2 hours.

I always use the same ferrules, because of that can not be removed of the column.

The vacuum is ok, but I notice that the air levels are higher than before (but inside the limits).

Can anybody help me?

You should not reuse the transfer nuts and ferrules, clip off the end and use a fresh nut and ferrule. Your air should disappear. I would also clip the injector end of the column. This would total less than 20 cm which for a 30M column will not affect much of anything.

If the samples are dirty enough that you have to change the column every month, and the system doesn't tune properly until you have cleaned the source, it is probably safe to assume the source is contaminated also. Why not just clean the source when the column is changed? The instrument is already cooled down and vented.

You can try to clean the column by passing sequencially methanol, dicloromethane and hexane. We work with salmon (a very fatty matrix) and after cleaning the column (and tunes) were well again.

Warning: You must check if your columns are solvent-washable!!!!!!!!

You need to condition the column before you couple it to the MS.

If you plug the column ends with a septum there is a significant chance that you get bits of setum into the ends of the column, so you need to trim the ends back, and then reset the nut and ferrule positions. If you want to leave the nuts and ferrules in position it is better to cap the ends with pieces a capillary tube pulled down to a taper like a press fit connector, and fused closed at one end. At one stgae one of the column companies used to ships its columns with these caps on the ends.

Peter

I use an HP 5890 and a HP58971A (older than yours). When I change column, I only can start working on the other day, because the ion source has a lot of air and water - it is normal. Instead to change the columns monthly why don't you clean only the injector and change the liners and septums?
I you vent the system to change the column, do not vent on the pump - the oil of the difusion pump goes to the font and you will need to clean everything...

atroguille,

Two things just occurred to me about this post. First, I had the same exact problem the other day when I shoved the column too far into the detector (probably beyond the source zone) on a 5973. At first I thought a dead EM (moment of panic) then I realized the error of my ways.

Second, why not put in a no-vent from SGE, Restek,???... Seems perfect fit for this problem.

Best regards.