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Dear David,


Further to my earlier message off list, yes, it is absolutely essential to
back out the column at 300 C for at least 12 hours. Anything lower
temperature-wise is a waste of time of helium.

Equally essential is isolating the source during bake-out (needle-valve)
and to increase the carrier gas pressure.

In addition, I strongly recommend to switch on the source and inlet heaters
as well as the diluter since the bake-out will release of lot crap from the
column, especially if for whatever reasons air got into the system at some
stage or time.

After the bake-out, keep heaters and diluter on for a while longer to avoid
"condensation" of bake-out eluents.


Cheers,

Wolfram



On Dec 17 2004, David Harris wrote:

> Thanks for all the ideas. Its looks like 90% of the problem has been
> solved by changing the molecular sieve GC column for a new one. I still
> have some tailing but much improved. I had baked out the old column in
> two overnight sessions at 250 C, it looks like this is not enough, at
> least not to recover the old column. The GC oven I use on this system can
> only just reach 250 C, it may be that I will need to use a different oven
> that will reach at least 300 C to properly bake out these columns. It may
> also be that the slight residual tailing I still see is because this new
> column may also need further bakeout before it is fully functional.