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Absorption of Light is a typical phenomenon of interaction between electromagnetic radiation and
matter. When a light beam crosses a substance, some of the radiation may be absorbed by atoms,
molecules or crystal lattices.
If pure absorption occurs, the fraction of light absorbed depends both on the optical path length through
the matter and on the physical-chemical characteristics of the substance according to the Lambert-
Beer Law:
-log I/I
o
= ε
λ
c d
or
A = ε
λ
c d
Where:
-log I/I
o
= Absorbance (A)
I
o
= intensity of incident light beam
I = intensity of light beam after absorption
ε
λ
= molar extinction coefficient at wavelength λ
c = molar concentration of the substance
d = optical path through the substance
Therefore, the concentration "c" can be calculated from the absorbance of the substance as the other
factors are known.
Photometric chemical analysis is based on the possibility to develop an absorbing compound from a
specific chemical reaction between sample and reagents. Given that the absorption of a compound
strictly depends on the wavelength of the incident light beam, a narrow spectral bandwidth should be
selected as well as a proper central wavelength to optimize measurements.
The optical system of
HANNA's HI 96770 colorimeter is based on a Light Emitting Diode (LED)
combined with a narrow-band interference filter to guarantee both high performance and reliable
results.
HI 96770 block diagram (optical layout)
PRINCIPLE OF OPERATION