chemical traps (5890 and others)

[MichaelVW]

I'm curious about these things. I'm thinking about getting a couple chemical traps for our 5890s. The ones inside are probably the originals. I took one out and just connected the gas lines directly because it seemed to be partly clogged - it was restricting flow to the injection port by a lot, and I couldn't get the injection port up to 15 psi even with the inlet regulator cranked up to 100 psi or so. I have to wonder if these things really make a difference. We've already got O2/moisture traps on our carrier gas lines.

Besides GCs, it seems that a lot of our equipment (purge & traps, autosamplers) also have pencil filters that, as far as I can tell, have never been changed. Ignoring them can't be uncommon - they're out of sight, a pain to get to, and I haven't seen them mentioned in a lot of troubleshooting guides.

What are they for? Have you ever found them to be a problem? Do you change them or ignore them? Has changing them ever led to observable changes in your equipment?



https://www.restek.com/catalog/view/562

[James_Ball]

The chemical pencil traps connected between the flow controller and the inlet are there to capture any bleed from the o-rings in the system prior to the inlet. If these tiny amounts of siloxanes would not be a problem for your analysis then they really would not be needed. I never saw that as a problem on any analysis we ever did. Most people running 5890s didn't even know they were in there until they became clogged.

If it is the trap between the split outlet of the inlet and the EPC that controls the back pressure, those will be clogged much faster and even if not clogged if that are saturated then the valves in the EPC that control back pressure and split flow are not protected and can go bad sooner. I don't remember if there was a trap on the 5890, and I am pretty sure there weren't any split traps if it had manual controls.

[pwm]

I saw a similar problem on a 5890 where the trap had been changed and inlet would not reach pressure no matter how much flow was added. It was not a restriction but a large leak at the filter. Either fitting wasnt tight enough or the oring was not seated right. I have seen a blocked pencil on a 6890 running Fatty acids. I think the filter youre looking at on 5890 filters gas coming into the GC, and not sample coming off the split line?

[benhutcherson]

If it is the trap between the split outlet of the inlet and the EPC that controls the back pressure, those will be clogged much faster and even if not clogged if that are saturated then the valves in the EPC that control back pressure and split flow are not protected and can go bad sooner. I don't remember if there was a trap on the 5890, and I am pretty sure there weren't any split traps if it had manual controls.

Every 5890 config I've seen(not that I've seen them all by any means) whether a regulator and dial or some flavor of EPC has just a outlet to exhaust to lab air for split(if a capillary inlet) and septum purge(all).

Those fittings ARE externally threaded, and I've seen traps hanging off of them. At least with manual pneumatics, it seems unwieldy to me if you're split injections since you have to use a flow meter to set your split ratio correctly, but I suppose if you always leave it the same it's not an issue. Of course, EPCs do at least calculate split flow for you, although you still have to manually set the "total flow" knob.