Chromatography Forum

I work in a research lab and use a GC/MS system daily. We have recently run into an issue with RSD and AUC between injections. I am getting 20% RSD between injections!! The original analyte was in petrolatum and was extracted out; however, some petrolatum remained in the extract. The liner could be dirty, but I would rather tweak inet parameters before yanking the liner. The solvent is acetone and we use an Agilent 7683 autoinjector. I've changed the needle and watched for syringe prime. I was using a 300C inlet temperature and splitless injections; I adjusted the method to 250C and a 10:1 split. Right now I am using caffeine to check everything out. Does anyone else have any suggestions? With such a poor RSD I am leaning towards a hardware problem.

If your peak shape has degraded to the point that your RSDs are on the rise due to integration problems resulting from baseline noise, as you said - It's time to yank the liner.

Seriously, if there's junk in the samples, it's probably time to replace the liner with a clean one and (assuming you're using a capillary column) chop half a meter off the inlet end of it.

If your chromatogram quality is presently comparable to what it was back when you had good RSDs (baseline noise is about the same, peak shape, heights, tailing factors are about the same) - then it's time to have a look at your injector.

I couldn't ask for better peak shape and the baseline is good. I just yanked the liner and it was dirty but not terrible. I replaced it and the o-ring, but with a good baseline I am assuming it's hardware.

Keep in mind that part of the point of a liner is than you can yank it. For some types of analyses, if you can see the dirt in the liner it is past time to yank it.