Reproducability problem on GC-FID

Hello Community

We have a reproducabiility problem on GC-FID's. We run an alkane standard every day in the morning. Peak shapes are looks good but when i compare the total area of the peaks over the last weeks an month, its very bad, i have a standard deviation of >15%. Here are some of the details of the instrument and method of the GC 6850A:

Method: inlet: 270°C, Split: 1:200 with a column: non-polar 20m/0.1mm/0.2µm. flow (H2) of 0.8ml/min
Oven starts at 50°C with a hold time of 0.5min, goes to 200°C in 6min.
Detector is at 290°C.

Alcane standard is in pentane. its 1.0µl injected on a split/splitless injector. We can already exclude injection problems with the autosampler and the syringe as we checked this throughout.

I hope i didn't forget any information needed for help solving this problem.

If you have an idea, please let me know.

Thanks a lot in advance!

have a good day

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