Chromatography Forum

Hi I am running a methanol standard in DMSO using 1 uL injections.

The injector system is CTC-CombiPAL. This system has always worked on the headspace but recently we changed it to direct injection. Using similar GC conditions, we noticed that the liquid injections gave poor peak height reproducibility but the peak areas counts are ok with varying amounts of peak tailing.

I have changed the liner, trim portion of the column but it does not seem to help.

Does anyone have experience with CTC injectors whether you need to reteach the syringe depth to go into the liner?

Or any idea what could be the possible causes of the irreproducible peak heights.

If the heights vary and the areas stay the same, the width must be varying - most likely as a result of the tailing.

Since you do not give any instrument conditions anything else would have to be guesswork.

Peter

What do you have the needle depth for the vial and the injector set at?

Also, what do you have the air volume amount set at? CTC recommends 0.5ul to 1.0ul.

The tailing thing sounds more like a column or flow control problem, but not for sure without knowing your conditions and parameters.

I would change the syringe after priming it by hand with your solvent. The syringe could be one of the many variables causing your problem