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The transmittance varies from 0 to 100. A transmittance of 0%T represents
complete absorption by the sample, whereas 100%T represents no absorption by
the sample.
The absorbance (A) is defined as:
A= log (1/T).
When the transmittance is 100% (T=1), A=log (1) = 0 and increases as the
transmittance decreases. The maximum value of the absorbance read by the
Alpha-1000
is 2.0. This represents a Transmittance of:
T=1/10
2.0
or about 1%. This is a very small transmittance and is essentially zero.
It is found that absorbance is directly proportional to concentration so that:
A=EBC
Where:
A=The absorbance
C=The concentration in moles/liter, and
B=The width of the sample cell or cuvette in cm
E=A proportionality constant called the molar absorptivity (measured in liters/mole-
cm)
The linear relationship between absorbance and concentration and sample cell
width is called Beer’s Law.
If we have a standard sample with a known absorbance and concentration and a
measured absorbance, it is easy to determine an unknown concentration of the
sample substance via linear interpolation. (See Figure-8)
Figure-8
Absorbance vs. Concentration
Absorbance
Concentration
