Method Dev. various questions

Discussions about GC and other "gas phase" separation techniques.

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Hello,

As always this forum is really helpful but I could not find what I was looking for.

I was wondering what should be the parameters on the unused second Inlet and detector while I'm setting up new methods.

I am injecting in the back Inlet and so I have no use for the front one but the method set up still requires conditions. So far I have set the inlet temp to 225 and the pressure to 5 psi since I am running hydrogen (gas economy and lab safety). Split around 350 I think. Basically I just wanted to some gas in the unused column so it is not affected by my temp programming.

As for the unused detector, I set the temp to 275 and shut down all gases and the flame.

Am I doing it correctly ?

Last thing, a few of my methods were overwritten by Chemstation (Open Lab CDS). I think I am not grasping the entire resolve / don't resolve concept on this software. Could you provide info on what is happening when I load a method and the system ask me to resolve or not.

Thank You !
Yes. I do this sort of thing as well. As long as your oven conditions in you method do not exceed the operating parameters (oven max. in particular) for the unused column, you should be ok.

Just go in, install the correct columns in the method, set all of the parameters and save the method. That "check for things that have changed" comparison helps to flag where things are different when you put a new column in (temp max/min, dimensions, etc.) or change the configuration somehow.
I normally just sent the unused column to something like 0.5ml/min flow if it is a 0.25ID column(may want a little higher for larger diameters) and have a split flow of about 20ml/min so that it keeps everything swept out and clean. I even have some setups where there are two columns going into a Tee fitting then into a MS detector, and it will work on those also. Usually set the flow to 0.3ml/min on the unused column and 1.2ml/min on the active one using 0.18ID columns. Trick it to make sure both columns are temperature compatible so you don't damage the phase by over heating. Otherwise it is really simple.
The past is there to guide us into the future, not to dwell in.
Setting the split to 350:1 wastes a lot of gas. Cut it to 30:1.

Peter
Peter Apps
Maybe I'm missing something (end of a long week), but if you do not use the other injector and detector (no column connected to them) you can just set them to off on the GC and software,
As your are using dual chennal (Two injector and two detector GC) and as per my understanding you have one column on front injector and another on second injector but at a time you are using only one injector for a run.

In my opinion you should keep the all other parameter same (except oven programming) which is require for your first injector and first detector so that at any time if you have to inject any sample on first injector you not need to wait for column conditioning of detector stabilization time.
As hydrogen is not so much costly but still you can look on your split ratio to reduce the consumption of hydrogen.

Need focus on your column maximum temp. if both are not equal than use less column temp. as maximum oven temp. on any method.
Thank you all for your replies.

We are running one ALS that we move to the port that we are using for the analysis.

Some of you were mentioning the high split ratio but it is necessary as to not overload the column (10M Column, 0.1, 100um). The goal was to decrease analysis time. Also, on my methods I always activate gas saver so the high split vent only last 2 minutes.

Thank you for your answers.
Canadian_Chemist wrote:
Thank you all for your replies.

We are running one ALS that we move to the port that we are using for the analysis.

Some of you were mentioning the high split ratio but it is necessary as to not overload the column (10M Column, 0.1, 100um). The goal was to decrease analysis time. Also, on my methods I always activate gas saver so the high split vent only last 2 minutes.

Thank you for your answers.


For the port you use that split is good, for the unused one you can just set it to a constant 20-30ml/minute when not injecting into it.

We do the same thing when we have a dual port/detector instrument. Just set up two columns for different tests and switch an injector tower, works very well and you only have one idle column instead of an entire GC sitting idle half the time which may not save much on gas but definitely saves on electricity, and it is always ready to go for either test.
The past is there to guide us into the future, not to dwell in.
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