response factor calculation

[pharmachem]

It looks simple but...

I always calculated response factor as area/conc. Recently I came across with response factor calculated the opposite, conc/area.
Which one is correct/recommended by the regulatory bodies? Please indicate the source.

Thank you.

[DR]

If you divide by the one or multiply by the other, you'll wind up with the same answer. If it's the right answer, RA won't care which version you use.

[Bruce Hamilton]

Just ensure you use the correct nomenclature, and are consistent within in-house methods. - You can't control defined compendal procedures.

Auditors tend to worry more about rounding errors and consistency of language, rather than being dogmatic about the calculation.

From the The European Pharmacopoeia 6th edition
[ Begin Extract ]
2.2.46. Chromatographic separation techniques

QUANTIFICATION

— Detector response.

The detector sensitivity is the signal output per unit concentration or unit mass of a substance in the mobile phase entering the detector.

The relative detector response factor, commonly referred to as response factor, expresses the sensitivity of a detector relative to a standard substance.

The correction factor is the reciprocal of the response factor.
[ End Extract ]

[aminamood]

From my background in environmental analyses, as a regulatory auditor, I'm a dog for calculations. I've seen too many times that lab's can "hide" fraud in their data, and we've found it through verification of the calculations.

The EPA methods often define the response factor (or relative response factor, or calibration factor) as response divided by concentration (or R/C). Response can be either area or height. But I've also seen, as you discussed, that some software quantitates RF as C/R (Thermo Target software).

The primary concern with this is that some EPA methods (8260B and 8270C, and CLP methods) have minimum reponse factor requirements based on R/C. Obviously, if the software quants C/R, then we end up comparing apples with oranges, and the lab really isn't evaluating the data appropriately. And the data may not meet the method requirements.

I just make sure that the lab's SOP clearly states the software's equations all the way to the final calculation of concentration that the lab will report, and that they've addressed any minimum RF issues.

[JI2002]

The primary concern with this is that some EPA methods (8260B and 8270C, and CLP methods) have minimum reponse factor requirements based on R/C. Obviously, if the software quants C/R, then we end up comparing apples with oranges, and the lab really isn't evaluating the data appropriately. And the data may not meet the method requirements.

It's easy to get around this. If the minimum response factor criteria is A for R/C, then it will be 1/A for C/R.