Chromatography Forum

Hi All,

I recently dirty soil samples through PyGCMS. Py unit is working fine after cleaning up the seals but GC pressure is failing to hold. The column is new, I changed the ferrules, changed the septum and split liner. It is still failing, I am wondering if I need to clean the split vent, I haven't cleaned it in 2 years. I am looking for instructional videos to clean it but I cannt find it. If you have suggestuions/recommendations please share. The unit is a shimadzu QP 2020NX with a GC-2030.

Thank you
Tasneem

I never worked with Shimadzu, just HP/Agilent; and on a couple of our units I had to clean out the split vent line. On at least one I increased the stainless steel tubing diameter.

I'd call Shimadzu and request instructions on how to do this.

Thank you, I have reached out to Shimadzu and waiting to hear back from them.

Is it a very regular procedure to clean vent line? Or is it supposed to be taken care of by the split filter? I am wondering if my problem is elsewhere.

So the issue we are having is GC is failing to hold higher pressure. I am thinking there is probably a block somewhere.

Changed the ferrules, septum, liner and cut a few cm of the column nothing solved the problem.

The error i mostly get is "Car1 AFC control irregularity" and one time I also got "CAR1 AFC valve not closed"
Please let me know if you have any suggestions.

Tasneem

Dirt in the split vent cannot cause a pressure failure, there is a leak somewhere. Do you have a leak seeker?

Actually it doesn't fail to hold a certain pressure, it holds pressure fine, its the split flow that is having issues. Split flow higher than 30 mL/min is becoming impossible to run. It lets me run split 20 or 10. But if I try split 50 and above it fails to hold the split flow.

I do have a leak seeker and I couldn't find anything.

For those specific errors, from Shimadzu:

https://faq.an.shimadzu.co.jp/faq/show/ ... in=english

(Basically check gas supply is at sufficient, at recommended values)

CARm AFC valve not completely closed:

"There is a leak inside the purge flow control valve of the AFC.
Answer
Check that the split line outlet and purge line outlet are not blinded.
If the error appears repeatedly even after checking the above, turn off the main power of the instrument, stop gas supply, and contact your Shimadzu sales/service representative."

https://faq.an.shimadzu.co.jp/faq/show/ ... in=english

Regarding cleaning the split vent line (not just changing the trap): the required frequency will depend on your analytes and matrix. This is common maintenance. Most GCs now do not have heated split vent lines (a Thermo Trace we had did, and that was an added feature we installed that was a nice addition). So any high boiling material swept out of the inlet during split injection may condense in the line prior to the trap. When the line gets gunked up enough, there can be an effect on the split vent flow which causes errors. This has happened to us more than once, so when we change the split vent trap, we also clean the line from the inlet to the trap. With Agilents, the line is just standard 1/8" tubing with standard Swagelok connectors; sometimes our lines are so fouled we just replace the line.