Chromatography Forum

I am not getting any peak for my sample loaded through gas sampling valve. But if i inject same sample directly through the injector i am getting a nice peak for my sample. I want to rectify this problem. Please give suggestion

This can range anwhere from a broken or improperly installed valve to an issue of technique. Can you give a bit more detail on how things are set up and what you have been doing?

I am using Agilent 6890A gc with FID
I am using HP-5 column, Oven-90: Inlet-170: Detector-250 degree centigrade
I am loading my sample through sample inlet-1 which is located left side of gc:

Your rotor might be installed reversed.

You may have the action of your valve operated in reverse order.

Or your valve may be blocked.

happy trouble shooting,

Rod

Thanks for the reply. DO i need to call Agilent or can i handle it by myself?

There is no reason to call Agilent unless you feel you are not able to touch the instrument at all.

I won't tell you it is hard to check out if the valve is operating or if sample flow is going through the valve at all, or if the position of the rotor is correct, because it is NOT DIFFICULT.

You should have a manual unless some fool threw it away. It happens !

It is easy for one with experience to give advice to the novice who doesn't know what is top or bottom with their GC. But if you have a manual and a diagram of the plumbing (both of which may be available on-line) I think most folks would give it a try There is not too much damage you can do. Just follow the pictures. Look on-line for the valve documentation. Agilent should have it posted and available for download.

First check your software that the settings are for a valve injection. This is PROBABLY the cause of your problem,............ really!

Then inject and see if the valve actually operates and returns to its original position.

Check to see if sample is flowing through the valve before and after injection.

Most installations have the output of the manual injection port passing through the valve and then to the column (Is yours so plumbed?).

What is the size of your sample loop?

Good luck trouble shooting.

Rod

First thing:
During the analysis you can see the valve switching?
If not the problem can be your method.
If so, make a leak test on the valve.

If you don't have leaks, check the pin switch on valve. This can be caused by the pin broken, then you can see the actuator works, but the valve don't switch and the sample not be injected on the system.

Some system are configurated with inlet between the valve and the column. I think this is your case, because you have peaks when inject the sample directly.