Chromatography Forum

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.

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".

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?

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

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.

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.