Hanna Instruments HI 83414 - Manual (Page 8)

8
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 is based on the turbidimeter tungsten lamp and a separate detector with a narrow
band interference filter @ 525 nm to guarantee both high performance and reliable results for
colorimetric measurements.
The measurement process is carried out in two phases: first the instrument is zeroed and then the
actual measurement is performed.
In this way the cuvette and the water turbidity are compensated during the zero mesurement phase.