Chromatography Forum

Is it possible to easily have two columns, each with a seperate injector, run (not simultaneously) one at time and use the same FID ? It would be nice if it was possible to shut off the flow from one column and just use one at a time. Is there an easy way to do this?

A simple Y connector would mean double the flow and would decrease the sensitivity I imagine.

The only 'robust' way that you could do this is to use a 4 port valve. This would enable you to select the column that you want to use with the FID and also allow flow in the column that you are not injecting into.

Gasman

Assuming you are using a 0.25mm ID columns, a simple 100% graphite ferrule with a dual hole configuration will allow you to insert two columns into the detector. The additional flow from the column (less than 1ml/min) will have little effect on your analysis. Cost: less than ten dollars

This is less costly than a valve which would require an isothermal analysis (low temperature limit also) to avoid damaging the rotor. The valve gives you a less inert flow path as well. Cost: hundreds of dollars

One could also use a metal 'T', with fused silica coating and a retention gap line (see Restek) entering the detector if two columns in the detector causes a problem. With 100% graphite ferrules a good seal will be kept even while programming the oven.
Cost: less than fifty dollars

Good luck,

Rod

Assuming you are using a 0.25mm ID columns, a simple 100% graphite ferrule with a dual hole configuration will allow you to insert two columns into the detector. The additional flow from the column (less than 1ml/min) will have little effect on your analysis. Cost: less than ten dollars

This is less costly than a valve which would require an isothermal analysis (low temperature limit also) to avoid damaging the rotor. The valve gives you a less inert flow path as well. Cost: hundreds of dollars

One could also use a metal 'T', with fused silica coating and a retention gap line (see Restek) entering the detector if two columns in the detector causes a problem. With 100% graphite ferrules a good seal will be kept even while programming the oven.
Cost: less than fifty dollars

Good luck,

Rod

Interesting Rod. It seems that a valve would make no sense for what I am asking.

Why would you think that two columns in the detectors would cause a problem? And also why would that be a solution only for a 0.25 column?

If you are working with capillary columns, then the tee will be a good solution. I would not worry about the two flows, as with a capillary column you usually need a make up gas for the FID to operate , so you would just lower the makeup gas flow so that the TOTAL carrier gas plus makeup flow is the same as when using a single column. The only 'danger' that I see is that you could get 'ghost' peaks coming off of the column that is not being used for the analysis.

Gasman

You would not want to have uneven lengths of column in the detector as the longer one COULD be source of sample loss for the shorter one. Plus, if the two columns would be 0.53mm ID then it could be a bit crowded in the passageway.

Gasman's concern about ghost peaks COULD be a problem but is not likely as long as you are careful with your samples and you program your oven properly, but not anymore than having one column could show ghost peaks.

If your instrument had a Dean's switch then that could also be used, but I would prefer a simple two hole ferrule over a valve, and I love valves being an old multidimensional GC guy that I am ! (one instrument I manufactured had 7 valves!)

good analysis !

Rod

[quote="chromatographer1"]You would not want to have uneven lengths of column in the detector /quote]

You are refferring to the lenght of the part of the column inserted into the detector ?

That's correct.

Rod

I think I would like to try out this solution.

How about the other way. One injector, with the ability to inject to two different columns going to different detectors (one at a time).


I have 2 injectors and 2 detectors in one machine.

I'd like to be able to use INJECTOR A and INJECTOR B with two different columns going to DETECTOR A.

I'd like to be able to use INJECTOR A with the same column as above but be able to connect to DETECTOR B as well as A.

There is no need for anything to run simultaneously.

This sounds like a job for a Deans switch, but unless you want frequent and rapid changes between inlet, columns and detectors, or to run unattended with an autinjector I would be seriously tempted to look at physically swapping columns around - have an inlet and detector nut permanently on each, and keep carrier gas flowing all the time.

Peter

An FID is not considered flow sensitive so keep column flow on both columns at all times. This will also minimize "ghost peaks". If it were me, I would put the outlet T in the oven and put one piece of megabore into the detector.

One injector to two detectors is a piece of cake, used to do it all the time in the environmental business (dual column confirmation.) There are a number of companies that can provide the materials to do this (two-hole ferrule or y-splitters...)

Regarding the 2 column, 2 injector, 2 detector configuration you speak of in your last post, are the detectors something other than FID's? If so, this may get a lot more challenging..... Otherwise, I am not really sure what you are trying to accomplish?

Best regards,

AICMM