Trimming the column

[ardee]

I would like to trim the column in my GC but was wondering how exactly to go about it. I have read that you shouldn't cool the injector because the nuts, ferrules etc will go through too much thermal expansion/contraction - is this correct? Should you change the ferrule when you trim the column or is it ok to reuse it? Also when you disconnect the column from the injector, aren't you exposing it to oxygen and making it vulnerable to damage? If so, how do you avoid this?
Thanks

[thohry]

You should turn off the inlet heater and wait until it's cool before replacing the column/or trimming it. This will prevent oxygen from reacting with in inside of the inlet and you from burning yourself.
If the column has been in use for quite a time, say, a couple of months, the ferrule should be replaced.

[sassman]

Assuming you are using a graphite ferrule, you should replace it every time that you re-seat the column. This will ensure a good seal. Allow the injector and column temps to cool to 30C before removing the column. You don't have to worry about air damaging the column while you are trimming it. If you plant to store it for a long time, you should use put a septum on the ends of the column to keep it sealed. If you have an electronic flow controller, you should re-set the column length in the program so that the calculated flow will be accurate.

[larkl]

I've never seen anyone cool the inlet to change a column. Sure seems like it would take a long time. Maybe there's a good reason for cooling it, but I've done it this way for years with no problems. I'd be more worried that the ferrule may not seal as well once it's heated.

[jh1]

I've never seen anyone cool the inlet to change a column. Sure seems like it would take a long time. Maybe there's a good reason for cooling it, but I've done it this way for years with no problems. I'd be more worried that the ferrule may not seal as well once it's heated.

It takes about an hour to cool down an inlet and reused ferrules seem to seal as well either way.

[AICMM]

I almost always turn the injector and oven off to change the septum or trim the column. I hate scorched fingers. I don't really worry about the column all that much. If using graphite or GV ferrules, getting a good re-seal is not really all that hard, especially if you haven't overtightened before. If using Vespel then check it again after it is hot (and I hope your running isothermal.)

Best regards.