Chromatography Forum

Dear all,

I'm quite new with ChemStation. We're trying to use a GC to analize air samples semi-continously. We are trying to define the method and to repeat it "infinitely".

We don't use an injector, but a gas sampling valve to load the sample. In a first attempt, we have used the Sequence Table from ChemStation to try to repeat the method twice by defining the Inj/Location as 2, but it only worked once.

Does anyone know what we should do to configure our GC to semi-continously repeat our method?

Thank you in advance for your help,

To run the ChemStation with valves, you MUST have one valve configured as a gas sampling valve. This need not be the actual valve that does the injection. I usually define a valve that is not physically installed on the GC as the gas sampling valve, for example valve 5 or valve 6. Once you have done this, you must then tell ChemStation that you are using this valve as the injection device. You do this in the 'Method and Run Control' screen. Click on 'Instrument' and then 'Select Injection Source' menu and a small window will appear that will allow you to select the valve as the injection device. Save your method.

You can now set up a sequence, entering '1' for the vial number and then in the injections per vial column, the number of times that you wish to run the GC. I believe that the maximum number is 99. If you need more, just enter another line into the sequence table. You must then start the sequence from the ChemStation, not by pressing Start Run on the GC.

Gasman

Dear Gasman,

thank you for your quick answer.

One of our valves is already selected as "gas sampling" valve. We did it as you mentioned but we actually operate this valve during the Method.

Today we did two tests by using the Sequence Table:

1. In the first one, the first line contained the name of the method we had created and 1 injection. A second line was added and it contained the same information as the first line.
2. In the second test, we used only 1 line. It had associated the method that had created and, as I mentioned before, 2 injections were selected in this case.

In both cases, the method run only once. Do you now why it did not run twice?

In the Sequence Table we observed that on the upper-right corner there are front / back displays, does it have some importance?

I thank you in advance for your help. If you think that you need some more information, please let me know.

Sincerely,

If you have two automatic injectors, you can have a sequence table for each one, hence the back and forward that you haver seen. If you are are working with one gas sampling valve, use the front sequence table and make sure that the table for the back sequnce is empty.

How are you starting your system? From your description of the problem, it looks to me as though you are starting the method. This will only run one time. You must start the sequence, then it will follow the sequence table.

Gasman

We have still problems trying to run a sequence with Chemstation.

We have a gas sampling valve (GSV) and a multiposition valve, apart from 5 other valves in the system. For the GSV we set a load time of 0.01 min and an injection time of 3.8 min. In the method's runtime table we do not include the GSV and the multiposition valve goes to position 2 after 0.55 min.

We have tried to run a sequence table by using one line, by defining the location as Vial 1 (i.e. the multiposition valve is at the first position in the beginning) and by setting 2 inj / location.

We click the button 'run sequence' from the sequence table and the method is loaded, but in the end it does not stop nor the 2nd injection starts.

I don't know what we are doing wrong. Why does not the method stop after the last command from the runtime table? Is there any setting we are missing to 'really' run the sequence? Do we have to set a 'post-run' to begin a new run in the sequence table?

I feel we are missing something evident but I cannot find it...

I really thank you for your help.

Would you please indicate what GC you are using and how all of the valves are configured. If this is an Agilent GC, can you please give me the serial number.

Gasman

Dear Gasman,

we found the problem, it was a little one: we had to set the time duration of the temperature in the oven...

Thank you very much for your attention.