Chromatography Forum

Yes, my column comp is on also I set up zero on the GC.

Thanks.

If you do not start a run on the 5890 by pressing 'START', but just increase the oven temperature to the final temperature of your temperature program, does the baseline still go negative?

Gasman

The base line changed with temperature if I pressed, “START “without injection.
I also tried isothermal test, I pressed “START” without injection and without temperature change, the base line moved to negative side.

You need to know what happens if you do NOT press Start run, but just put the oven temperature up to the final temperature of your temperature program. This will tell us if it is a 'chromatography' problem if you still see the baseline go negative.

I have the feeling that you have a baseline compensation run stored in your GC, and the signal chosen is something like 'A -ColComp1'. If the compensation run was made on a column that had not been conditioned correctly, then it is possible that the compensation signal is greater than the present bleed of your column. This will give you your negative output.

Do what I say at the top of this message, this will tell you immediately where the problem is. If there is no negative signal by just increasing the oven temperature, check what your signal entry is. If it has the '-ColComp' as part of the signal, remove this by just entering A or B for your signal.

Gasman

Thanks for all helps,

After removed “Col Comp” the signal has no baseline problem.

Nice catch on the column comp setting folks.