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Response factor or correction factor: is there a difference?
Posted: Wed Mar 05, 2008 8:11 pm
by mojo
I is testing Meloxicam API for related substances as per BP. The calculation refers to a correction factor. Can someone please explain me the difference between response factor and correction factor? The correction factors range from less than 1.0 to greater than 1.0. Why is this so?
Posted: Sat Mar 08, 2008 7:20 am
by Bruce Hamilton
I'm not familiar with that method, but they are different.
The pharmacopoeia tend to define terms, but there can also be other definitions, refer further below...
The EP ( which the BP also uses ) defines both in Section 2.2.46, and I suspect the BP will as well...
" 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."
OK, so that's what they use,... However, other published methods may also use "correction factor" to help define differences between detection wavelengths ( eg reading at two wavelengths because some impurities have different UV spectra to the API ), and also chemical forms ( eg a standard material might be tetrahydrate, and the actual compound is the monohydrate form ).
Confused?. It's important to look at the actual definitions in the particular compendial source that the method is from.
Please keep having fun,
Bruce Hamilton
Posted: Mon Mar 10, 2008 8:19 am
by gcguy
If you plan to use chemstation then it might well be that correction factor and relative response factor are not the same. RRF, as we calculate it, is the difference in response factor based on areas and weights. For two analytes run at the same concentration we would measure the response of each and normalise the weights to that of the normal calibrant. The ratio of the areas is then the relative response factor. Using Chemstation it is not possible to divide, only multiply. Therefore we would apply a multiplier which would be the reciprocal of the RRF, this way we let chemstation do the arithmetic.