I am trying to analyse nitrogen gas from a sample bag by GC with a TCD detector. I need to know how to get the sample onto the column, preferably an automated sampler and not manual inject. I already know about gas tight syringes but any other info would be useful . Have an HP 6890

You need a 6 port Valvo or other company valve with an external sample loop (an LC sample valve would work)

You would connect the inlet port of the valve to the bag and flow gas from the bag through the valve and onwards out the outlet port of the valve to ambient pressure. Then automatically operate the valve or manually operate the valve to empty the sample loop contents onto the column which is, of course, connected to the valve in some manner.

See VICI catalog for help. (Valco Industries in Houston)

Take care about contamination because in a bag it is to easy that air comes into that and the result could be wrong.

From anonymous 3

I sometimes do this. I have a multiport Valco valve with 1/16" inlet/outlet tubes. I attach plastic tubing to the outlet, connect the bag to the inlet, press down hard on the bag with a lot of body weight to get a flow going, put the outlet tube in a beaker of clean deionised water and check for bubbles so I know the loop is being flushed before activating the valve(but don't let the water suck back into the loop afterwards!).

I too do the same as anon 3, but I pull a chair over to the GC and sit on the bag for a about a minute. Now I can see the bubbles and not as much effort into pushing gas through the 1/16 tubing.