Chromatography Forum

We're doing on line gas phase analysis, for automatisation we had to replace the former valve with a new one which has smaller ports (we replace all the 1/8" tubing by 1/16")

The GC is equipped with an injector, for liquid injection, and currently the gas samples also go through this injector.

Question: is it possible to bypass this injector for the gas samples?
if yes, how?
would just a normal connection from 1/16" tubing to column do or do we absolutely need a liner?

Thanks

trigger,

I suspect the reason your sampling valve is plumbed to your inlet is because you are doing a split injection. Without more details it is difficult to say. Having said that, if you are doing split, then it is probably being done to control the amount of material on column. In which case, no, you do not want to by-pass the injector.

I guess the other question is why do you want to? What is it about the chromatogram that you don't like which makes you want to by-pass the inlet?

Best regards.

there is no split on the injector, it's there for liquid injection which we don't use.

even if we don't bypass the injector in the future the same question will appear on how to connect the column to a 1/16" tubing (we want to had a stripper column)

for very practical reason (avoid to make a hole in the oven) if we can completely remove the injector then we can use the hole to pass the connection from the valve to the stripper column

Connection of a GSV via a liquid injector is the usual route as this allows splitting of the sample and it is easy to divert the carrier flow through the valve and back into the injector. This gives the most flexibility. There is no reason why you should not connect direct to the valve, you can get capillary ferrules for Valco 1/16" fittings should that be the valve you are using

yes, you got it!!
so then we can connect the column directly to the valve, and it wouldn't be a problem to have about 20cm of the column out of the oven?

thanks for the answers!

yes, you got it!!
so then we can connect the column directly to the valve, and it wouldn't be a problem to have about 20cm of the column out of the oven?

thanks for the answers!

It sounds like your sample is being injected while at ambient temperature, and your gas sample valve is also at ambient temperature. If this is the case, it would be best to connect your column to the sampling valve using a section of blank capillary tubing (no phase).

Whether or not your sample can pass through a cold section of your analytical column without detrimental effects on the chromatography depends on the specifics of your analysis (starting oven temp, column phase, sample composition).

The sample will be ambient air for VOC analysis

The valve is at ambient temperature, and the temperature program will be starting a few degrees above room temperature and very likely isothermal.

In case of the use of a stripper column would it still be necessary to use blank capillary tubing?

What would be the effect of having a cooler section on the column? (Let’s say 20cm on a 15m capillary column or on a filled column?)

I would use a short length of 1/16" tubing from the valve to a 1/16" union. Then attach the column to the union with the appropriate ferrule (I would use the Valco One piece fused silica adapter). The reason is that if you attach the column or a piece of FS directly into the valve, you will have a hack of a time getting the ferrule out of the valve at a later date. Been there, have the T-shirt. This can really be a headache depending on the valve access. Using the union, you can take it out and work the ferrule out or just use a new union.