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- Posts: 2
- Joined: Sun Oct 04, 2020 7:36 pm
Firstly, thanks to all, admin and users for the work, this is always a good place for information. Sorry if it is not the appropriate place for posting, I was in doubt between this and sample preparation, and also I look for something similar but find nothing.
There I go. Briefly, I want to quantify some sample previously trapped in a cold trap, basically a u shape tube in liquid nitrogen. I want to raise temperature and quantify what was trapped before, but I have serious doubt about how to do it and do it in a precise and reproducibly way.
Explaining a little more, I want to make some treatment to a sample trough inert flow, it will desorb some gases at ambient temperature, like ammonia, in a small quantity (around 0.5ml STP) wich would be freeze in the nitrogen trap. I have an online chromatograph with a valve injection and a FID detector wich could be connected (or not) to the end of the trap.
I have experience with GC for quantifying from continous reactors and manual injections of liquid samples but when I think in this issue I see obvious troubles. If I raise temperature and push the gases previously trapped they would not be in the loop for the injection (at least not at the same quantity). Taking into account the typically layout of a injection valve(at least for me), while loop is filling with sample flow chrom carrier is going into column, when switch to the other position, carrier pushes sample from the loop into column. So if I raise temperature and inject nothing assures sample goes into column in a reproducible manner. The same thing applies for using a continous flow as standard.
I thought in how to fix it and maybe it could be done in a very unusual way, for me, changing valve ports and making sample inert act as "carrier" of the chromatograph when switch the valve, and inject all the sample into the column but anyone who has change or fix an injection valve knows that is a very annoying stuff, so small and dedicated the tubes, and this is not a operation to do with regularity in order to keep equipment versatility. Chromatograph is an old one, manual gas valves, so I think there wouldn't be electronics/software problems. By the way i would like to ask to you: do you think there would be any column/detector problem by injecting 1STP ml of gas sample into a 1/8" packed column ( for example tipical porapak q, p or N)? Taking into account that there would be not too much resolution problem (only 2 or 3 compounds with diferent polarity)... I think there's no problem, but would be nice knowing your opinion.
On the other hand I thought in calibrate volume of the trap (with pressure system), put a septum and take some known volume sample with a syringe and inject manually but possibly temperature-pressure variations in trap, human errors with volume of sample taken mixed with absolute calibrate makes me mistrust with the precision of quantification.
I have seen something similar for concentrate and quantifying VOCs but only comercial ones and can not find how it works.
Sorry for message length, maybe it is more simple than i am thinking. I try to synthesize to the fullest and make it understable (maybe do not achieve), so omitted some thecnical aspects like flow, equipment, but if you consider it relevant, please do not hesitate in asking and i will try to explain it better. Also sorry about probably technical mistakes
All ideas, advice or reports would be very welcome.
Thanks in advance for your response