Chromatography Forum

we are using gc 6890 ecd/tcd. on front place capillary column and ecd are instaled, on back place packed column with tcd. our question is:
- when we are working on front place, should be tcd turned off or on?
we have gas flow on while the temperature is off.


- we also have high signal on ecd - about 350 for baseline

thank you for your help,

FH

If you are not using the TCD then leave it turned off, and by this I am refering to the filament and switching gas. You should leave flow on through the packed column, and it would be wise to leave the TCD temperature on. If you are using a temperature program for the ECD channel, then I would set the temperature to about 50'C higher than the final temperature that you have for your temperature program. Also, make sure that this temperature is NOT higher than the maximum temperature allowed for the phase that you have on the packed column.

Gasman

Gasman,

Why is it better to leave the TCD temperature on? Are there any drawbacks to turn it off? I'm more concerned about running out of carrier gas when GC is idle.

If you have column bleed it would condense in the TCD, so by keeping the temperature higher than the final temperature of the program you are using on the ECD channel will minimize condensation of any liquid phase. If you are using a molecular sieve column or carbon sieve type of column, this would not be a problem, and you could leave the temperature off.

The switching flow on the 6890 TCD is about 1.5 times higher than the column flow, so if you are using a 1/8 inch column, your column flow would most likely be about 30ml/min, and hence the switching flow would be about 45 ml/min, giving a total of 75 ml/min. By turning the TCD filament off, you would thus turn off the switching flow. I would then drop the column flow down to about 10 ml/min to keep the column clean and air getting into the column.

Gasman