Chromatography Forum

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 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.

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

If you inject 1 ul into a split injector with a 100:1 split (for example), how much goes onto the column ?, and how much of that is in each of (say) 10 peaks at the detector ?

You may be right that response for the analysis is not linear, or equal for all analytes, but it is more likely to be due to inlet discrimination than to detector linearity.

Peter