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- Posts: 6
- Joined: Mon Mar 13, 2017 4:19 pm
I run 2 Varian CP-3800 chromatographs, they both have Front TCDs and Middle FIDs. I use Helium as a carrier gas and run natural gas samples taken off of various pipelines in a high-volume oilfield area. Both machines look for C1-C6+ natural gas components and also identify Nitrogen and CO2 content on the Front TCDs.
The problem I'm having is, I can run a typical day's worth of samples (about 20 per machine) and run a "blank" using just helium afterwards and get clean results one day, a few days later I run a "blank" using the same procedures and get peaks that contain the same gases I look for in my results. The peaks mainly show up on my Front TCDs, I rarely have anything show up on the Mid FIDs.
I typically purge my lines for at least a minute or more at around 100psi or a little higher when I run the helium "blanks."
I've changed filters on my carrier gas inlets and on my sample inlets and cleaned everything I can think of. I am wondering if anyone who has run similar types of gas samples have ever run into this problem? The "blank" results that have peaks are random, as in the gases that are identified one day are different from the ones that are found the next time. Is it possible that somewhere in my lines something could be "trapping" part of a previous sample? I've shortened my injection lines as much as possible and as I said I've changed filters recently. I understand that my question may depend on the physical makeup of my machines but I still have to ask.
The problem isn't confined to just one machine but it does repeat on one more than the other. I have performed a bake-out recently (up to 240° C for 2.5 hours) on the one machine it happens more often on and it cleared up immediately after but started again a few days later. As I said the peaks don't appear every time I run a blank, which is the most confusing part, and the gases that appear are random as well. Thank you all in advance.
The problem I'm having is, I can run a typical day's worth of samples (about 20 per machine) and run a "blank" using just helium afterwards and get clean results one day, a few days later I run a "blank" using the same procedures and get peaks that contain the same gases I look for in my results. The peaks mainly show up on my Front TCDs, I rarely have anything show up on the Mid FIDs.
I typically purge my lines for at least a minute or more at around 100psi or a little higher when I run the helium "blanks."
I've changed filters on my carrier gas inlets and on my sample inlets and cleaned everything I can think of. I am wondering if anyone who has run similar types of gas samples have ever run into this problem? The "blank" results that have peaks are random, as in the gases that are identified one day are different from the ones that are found the next time. Is it possible that somewhere in my lines something could be "trapping" part of a previous sample? I've shortened my injection lines as much as possible and as I said I've changed filters recently. I understand that my question may depend on the physical makeup of my machines but I still have to ask.
The problem isn't confined to just one machine but it does repeat on one more than the other. I have performed a bake-out recently (up to 240° C for 2.5 hours) on the one machine it happens more often on and it cleared up immediately after but started again a few days later. As I said the peaks don't appear every time I run a blank, which is the most confusing part, and the gases that appear are random as well. Thank you all in advance.
