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- Posts: 11
- Joined: Fri Apr 09, 2021 6:18 pm
I'm having some trouble with a GC-FID method and I would like to share it with you in order to find a possible cause.
I'm trying to implement a GC-FID method in a new Thermo Trace 1300 we recently acquired in our lab, for two analytes (let's say A and B). It's a brand new chromatograph so I guess we shouldn't have leak or dirtiness or these kind of problems.
The method is tested in our old Agilent 6890 and apparently it works propperly: correct calibration linear curves (7 calibration level, ISTD method), daily controls yielding the target results and routine samples of known concentration yielding also valid results.
The instrumental methods in the new Thermo have the same "basic" conditions than used in the Agilent one (column flow, inlet temperature, split ratio, oven temperatures (two ramps for A, one ramp for B), FID gases flows and temperature, etc.
The thing is that after having injected both calibration curves in Thermo, A gives nearly identical results but B gives such a lower relative response factor and slope than for Agilent.
(aproximate) slopes for :
A: 0,56 --> 0,55
B: 0,64 --> 0,53
My question is that if there may be other method conditions appart from column flow, inlet and oven temperatures or detector conditions that I could be ignoring and may provoke a low response factor. I have started by testing with oven equilibration time and it doesn't seem to affect much (althought it has increased both responses of analyte and ISTD). I looked for dirtiness in the liner and it was quite clean so I discarded this cause too. I am thinking of other options such as injection pasrameters or others ... I'm not an expert and I'm a bit lost with parameters that don't appear in the Agilent method.
Both curves have been injected in both chromatographs within days/few weeks of difference, so I don't believe it's a problem of degradation of the calibration levels solutions.
I'm sorry for all this long writing, I wanted to be clear. If you need some method details such as flows or temp's, don't hesitate to ask.
Thank you