The actual pressure of the column can't reach the set pressu

[Jing]

Dear all,

I'm new with GC and I haven't got proper training. I'm using a GC-FID (Chrompack 9002). I have some problem with it now.

Sometime ago, the reproducibility of my standards were low after I cut off some column at the injector end and cleaned the injector liner. I shut it down for two weeks and restarted it. I injected some DCM first. This time, the DCM peak appeared very late. Someone suggested me that there might be a blockage in the column. Then, I cut off about 30 cm off the column at the injector end. The actual pressure was very high (about 190 kPa) and the GC couldn't be ready for injector.

I took the injector liner out and cleaned it. Put it back on. When the injector temperature is 200 degree, the pressure is lower than the set pressure (100 kPa). When the injector is cold, the pressure is higher than 100 kPa.

When our GC ran normally, the pressure went up to 190 kPa, then dropped back to 100 kPa rapidly. Now, even I turn off the carrier gas cylinder, it takes long long time to get to zero.

Please help me with this problem! Any suggestion will be really appreciated!

Cheers,

Jing

[Jing]

Can anyone help me with this problem please? I really need help to solve the problem. I've got many samples waiting to run on the GC.

Thank you in advance!


Jing

[dlorenzo]

Dear friend:

I don't understand your problem, because are not common symphtoms on an injector.
But first of all, I would check the system without column, placing a blank nut in the injector outlet. Close the split valve and purge. Check the pressure, with the injector cool and then hot.

Let me know the results of this test. I hope can help you. Sorry about my english but I'm born in South America and speak spanish.

Sincerely yours

DL

[Les]

First sounds like blockage and leaking at the same time. Have you checked the FID for blockage. Sometimes as columns age, pieces will lodge in the jet.

[sanjay]

Deart Jing


I guess itis a instrument problem plus operational problem from you message GC configuration is split splitless injector with fid.

I dont understand "When GC ran normally pressure went up to 190Kpa then dropped back to 100 kpa" & really it is not require to cut 30 cm leangth of column ( hardly 4/5 cm is ok if you have dought of column blockge)

As you said when injector is 200 pressure is lower then set pressure it must be leak in ijector or at the column end fitted at injector. change nut ferrule at injector end also put proper parameter for column leangth , id as it may ask for column flow setting.


regards
sanjay

[Jing]

I'm so happy there are a few replies. Thank you very much for all your replies!

To dlorenzo:

I'll do what you suggested me to do. There is just one question. I don't know if I can use a normal nut to fit the injector end when taking out the column.

To Les:

As I said before, I'm new with GC-FID. So, would you please be so kind to tell me how to check the blockage in the GC? Should I use bubble flow metre (I can just find this here) to check the carries flow? If you can suggest some reading material to me, it'll also be very helpful.

To sanjay:

I set the pressure to 100 kPa. I observed the pressure before. When I cleaned the liner before, I set the pressure to zero first. After I put the liner back, I changed the pressure back to 100 kPa. The pressure went up to about 200 kPa, then dropped back to 100 kPa (set point). It seems to me that the pressure couldn't drop to 100 kPa now.

Many thanks again to all of you!

Jing

[dlorenzo]

Dear Jing: to close the injector outlet, you must use a nut (it have no hole) that generaly is provided with your system, if you don't have one, you must purchase it.
Other choice is to fit a column ferule with a piece of stainless steel with the same diameter of your column and use the nut you often use with your columns.

Best regards and good luck

DL

[semivoadude]

Try agilent.com and restekcorp.com for online support. I run a GC fid 5890 and these resources are very helpful.

[law_son]

The first thing that I would check is to see that the column is seated to the right depth on the inlet and the detector side AND that you didnt over tighten your nuts and cracked or crimped the column on either side (assuming at 30m its a cap or megabore column).

That would be the quick and easy check, after that what is proposed above is a good route. Calling the Mfgr is always a great option, they can walk you thru some quick checks on the phone and often set you in the right direction from there.

Good luck and keep us posted, its always good to hear the solution to the problems and concerns people post.

regards,

~law_son