Dear all,
In our lab we have thermal desorption on line with gas chromatography coupled to a mass spectrometer detector for VOC identification and quantification in indoor air samples. The GC used is from Agilent Technologies, model 6890N and the mass spectrometer detector is from Agilent also, model 5973. The thermal desorption system was from DANI, model STD 33.50.
We recently bought an ATD 350 to replace the old equipment from Dani Instruments (that worked for almost 25 years) but we are having some (a lot) problems...
Since the day the ATD was installed our baseline has much more noise than the one with the old TD equipment and for temperatures of the oven higher than 200ºC we have an intense bleeding of the column.
Moreover the o-rings in the ATD that 'hold' the tube seems to have a life time really short (about 50 analysis) which is unacceptable for us since it is about one week of work before they are completely damaged.
Does anyone has experience with this?
I would appreciate any help.
Thanks,
Anabela
Hi Anabela,
I've found a discussion thread here:
https://www.chromforum.org/viewtopic.php?t=5573
Regards
Markus
Thanks Markus Christ
The problem is not exactly the same, however the behaviour of the technician is. He is always suspecting of our "side", the GC column, the oven program, the helium...the ATD is never the problem!
Anabela,
It looks like different issue's.
The bleeding is not related to the sampler, columns do age and this can be accelerated by contamination (O2, H2O,...). You can always monitor the lower masses (4,18,28,32) with the msd.
About the O-rings, there are two type's, low and high temperature one's. We always use the high temperature one's, this may also reduce the background. As he are doing quiet rough stuff on our TD, we had troubles with the filter between the tube and the valve (and everything behind!!!) so we backed up the normal (teflon?) filter with a metal one (also from PE). We have the impression (no routine work) that this increases the live of the o-rings. Often a leak at the lower seal is created by 'dust' on the o-ring, a cotton swap moistened with methanol solves the problem. Also check your tubes, they may be 'deformed' towards the Dani.
Last remark, the inlet split has a huge influence on contamination and carry over
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