Chromatography Forum

Hello,
I'm looking for advice in putting together a GC system for use in OChem lab. So it should be cheap and easy to run (nitrogen carrier gas...). It does not need high sensitivity, but speed is helpful. Our lab procedures were originally written for use with GOW-MAC's...

Budget-wise, I have to use the Agilent 6850 that I have available: purged packed injector and TCD detector. I want to be able to use the Autoinjector I have with it. I'd still like to get capillary column peak resolution, so I guess I should put in a middle-sized column? ID=20um? 5um?

But I don't know what column dimensions are compatible/advisable with this port/detector combination--I've only ever used split/splitless and MSD, where everything is really small. I don't know what flow rates the TCD works with, so I don't have a point of reference for columns. I don't know what sample volume to aim for if I'm not using a split injection.

Thanks

I have a 0.53mm x 0.5um RTX-50 column I could put on there. Does that sound like a reasonable place to start for the purged packed/ TCD ?

Good starting point. You may need makeup gas at the detector inlet though if it requires something like 30ml/min to operate.

Right, except that I just realized this RTX-50 column is wound up on a hanger that's too big for the 6850 oven...

Depending on what you want to demonstrate.....

A megabore (0.53) can be run with a packed inlet (they were originally built for that very idea) and you can run them with pretty high flow rates (20 mL/min for example.) With nitrogen carrier the sensitivity will not be all that great on a TCD so you should think about 10% level solutions (say a hydrocarbon mixture of 25 % each.) With 6850 the total TCD flow should be 2X to 3X of the column flow.... Optionally, you can run hydrogen carrier and do lower level analysis although probably still not below 0.5% say...

One other option, a PLOT column and you measure hydrogen in a sample with a nitrogen carrier or CO2 in room air versus outdoor air with a hydrogen carrier...

Best regards,

AICMM