Response factor

Response factor, usually in chromatography and spectroscopy, is the ratio between a signal produced by an analyte, and the quantity of analyte which produces the signal. Ideally, and for easy computation, this ratio is unity (one). In real-world scenarios, this is often not the case.

Expression

The response factor $f\_i$ can be expressed on a molar, volume or masscite journal |author=Ramus TL, Hein SJ, Thomas LC |title=Determinations of polychlorinated biphenyl isomers by response factor calibration |journal=J. Chromatogr. |volume=404 |issue=1 |pages=155–62 |year=1987 |month=August |pmid=3119645 |doi= |url=] basis:

:$f\_i\; =\; frac\{A\_i\}\; \{A\_\{st\; f\_\{st\}$

where A is the signal (e.g. peak area) and the subscript "i" indicates the sample and the subscript "st" indicates the standard. [cite book | last = Orange Book | first = | authorlink = | coauthors = | title = Compendium of Analytical Nomenclature | publisher = IUPAC | date = | location = | pages = | url = http://www.iupac.org/publications/analytical_compendium/Cha09sec242.pdf | doi = | id = | isbn = ] The response factor of the standard is assigned an arbitrary factor, for example 1 or 100.

Examples

As a positive example, the response factors of each hydrogen atom in a sample analysed by proton NMR is unity, or very nearly so. Thus, by comparing the integrals of each peak observed in a proton NMR spectrum, one can determine composition of an arbitrary analyte mixture. Alternatively, one can determine the ratios of protons in various chemical environments in a single pure analyte.

On the other hand, for gas chromatography-mass spectrometry, the total ion counts of different species in a mixture may not produce peaks of similar area per unit of analyte due to the different susceptibilities of fragmentation. As a result, comparing the peak areas of different compounds in a chromatogram, one may not determine the relative proportions of each compound in the mixture.

References