Another note: for any material from the TC/EA, such as phosphates, that
might travel with the carrier gas, we use a stainless steel 1/16 inch loop
trap at liquid nitrogen temperature. After the runs are over we have a
valve that diverts the He flow before it reaches the Conflo. The trap is
then thoroughly baked out and left to vent for the rest of the evening.
There were no changes in peak shape or isotopic compositions using the
trap with either dry ice/ethanol or liquid nitrogen.
> 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
> as well as the diluter since the bake-out will release of lot crap from
> 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
> "condensation" of bake-out eluents.
> 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
>> only just reach 250 C, it may be that I will need to use a different
>> that will reach at least 300 C to properly bake out these columns. It
>> 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.