Provider: ingentaconnect
Database: ingentaconnect
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TY - ABST
AU - McDowell, Robin S.
TI - Quantitative Photometric Analysis Using Absorbance Ratios: Optimizing Peak Transmittances
JO - Applied Spectroscopy
PY - 1972-05-01T00:00:00///
VL - 26
IS - 3
SP - 405
EP - 406
KW - Errors
KW - Intensity measurements
KW - Accuracy
KW - Absorbance ratios
KW - Sampling
KW - Photometric analysis
KW - Quantitative analysis
N2 - The relation between given relative errors in transmittance (*T = I/I*
_{o}) and absorbance (*A* = -log *T*) in photometric analysis is

Δ*A*/*A* = – (log *e*)Δ*T*(10^{
A
}/*A*). (1)

If Beer's law holds,
the concentration of a substance is given by

*c* = *A*/*ab*,

where *a* is its absorptivity at the wave length used and *b* is the path length; the relative error in the concentration, Δ*c/c*, is then just Δ*A/A*. If it is further assumed
that the error in measuring the transmittance is independent of *T* (i.e., that Δ*T* is constant), then differentiation of Eq. (1) shows that Δ*c/c* is minimized for *A* = log *e* = 0.43, or *T* = *e*
^{−1} = 0.37, at which point
| Δ*c/c* | = *e*Δ*T* = 2.72Δ*T*. The minimum is a rather flat one, and the useful analytical range is generally quoted as about 20 to 60 % *T*.
UR - http://www.ingentaconnect.com/content/sas/sas/1972/00000026/00000003/art00015
M3 - doi:10.1366/000370272774352047
UR - http://dx.doi.org/10.1366/000370272774352047
ER -