FID detector linearity response factors

I got a data sheet for my Agilent 7890 FID detector. The stated linear range is 10x7. This range I think should mean that from 1% down to 0.1 ppM the detector is linear for Tridecane. I figure concentration-wise in splitless mode - that works out to be 10-ug per 1-uL injection at the high end, down to 1-ng per 1-uL.


Over the years I have worked in labs that have injected neat samples with a split ratio and reported area percent values to production with FID. Given a one microliter injection, a hypothetical neat sample could be equal to a 1-mg injection. *Since 1-mg is 100x the maximum linear range amount for FID -- is there a valid argument that one should not report neat samples by FID and area percent, since the various components responses would not be linear? Specifically, the main assay peak linearity vs. the much smaller impurities. Questioning if main component peak would be under-reporting relative to impurities in high assay samples.


Give this a little thought in case my reasoning is flawed, and let me know if I am in error.

  • FID goes up to range of % yes. Linearity of a component is not determine really by what Agilent says, but by what your calibration says. If they have a calibration of 0.01%-10% and the response is linear (you can make a linear graph of concentration by signal) then the response is linear. 

    Now if you are at the limit of what the FID can do, you can have issues sometimes. Maybe if they change FID for x reason, the response is not linear anymore. But that we cannot really tell until you try it with your detector. Also, if your sample is not really clean, you can create issues in your inlet, column or detector. But that is for them to judge.

  • Just to make it more clear, what we say about the detector range is to give an idea of sensitivity. It is not a hard limit.

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