Broad peaks

[kdamme]

On a double-channel system with Varian 1079-injectors I inject a 250 ppb solution:
1) 5.0 uL on a 25m 0.25mm DB-5 column with DF=0.25 gas flow = 1.3 ml/min.
2) 2.5 uL on a 50m 0.25mm column with two different phases DF=0.1 gas pressure is 22.5 psi

Both columns have a 4m 0.53 mm retention gap connected with a press-fit.

The DB-5 column gives no problems when connected to any of the injectors but the other column gives broad peaks from the first (Hexachlorobutadiene) to the last (Mirex) peak.

Further information:
Solvent is petroleum ether, boiling point 30-60 C.
Column oven temperature is 40 C on injection and a temperature program starts after 1 minute (25 deg/min to 140 and from there on 5 deg/min to 300).
Detection by MS (1) and ECD (2).
ECD temperature is 320 C, make-up gas nitrogen at 25 ml/min.
I tried injections at 270 C splitless, and later PTV at 45 C for 0.1 minute followed by a 200 deg/min ramp to 350 C .

Solvent shouldn't be changed. Endrin is one of the components in the method.

All settings so far give broad peaks. I suppose that I overload the column, but am not sure. I have contacts with our supplier on the problem but all suggestions are welcome.

[Consumer Products Guy]

I suppose that I overload the column, but am not sure.

A good rule of thumb for chromatography is to decrease injection size and/or concentration, then ask yourself if the chromatography "got better, worse, or the same".

[thohry]

On a double-channel system with Varian 1079-injectors I inject a 250 ppb solution:
1) 5.0 uL on a 25m 0.25mm DB-5 column with DF=0.25 gas flow = 1.3 ml/min.
2) 2.5 uL on a 50m 0.25mm column with two different phases DF=0.1 gas pressure is 22.5 psi
All settings so far give broad peaks. I suppose that I overload the column, but am not sure. I have contacts with our supplier on the problem but all suggestions are welcome.

What is the stationary phase of the 2nd column?

[Peter Apps]

To save long discussions about peak shapes please post a chromatogram - then we can all see what we are talking about. Instructions are in a sticky at the top of the LC page.

Peter

[kdamme]

A chromatogram will be posted tomorrow.

Stationary phase of column 2 is: CP-SIL5 / 18CB (Varian CP7477) for PCB. PCB peak shape is the same as other chlorinated components.

[kdamme]

Oops, I found what was wrong...

The column was the problem. Replacing it by a new one gave sharp peaks again. Maybe I injected a wrong substance. I don't know.
Didn't expect this was the problem anyway, because it was a relatively new column.

Sorry I took some of your valuable time, I should have checked it before posting.