Electro-Chemical Devices (ECD) CA6 Hardness Analyzer - Manual (Page 19)

Typical absorbance values range from 0 to 1, but it can be greater than 1.
When the absorbance is 0 then none of the light passing through the sample is absorbed. The intensities
of the sample and reference beam are both the same, so the ratio Io/I
1
is 1. Log
10
of 1 is zero.
An absorbance of 1 happens when 90% of the light at that wavelength has been absorbed - which
means that the intensity is 10% of the blank sample reading.
In that case, Io/ I
1
is 100/10 =10 and log
10
(10) = 1.
2.2.1 Absorption photometry (Colorimetry):
The methods used are based on the formation of a colored complex of the analyte with a color reagent.
Light with a specific wavelength is transmitted through the reaction mixture. The absorbance of light by
the formed complex is measured by a photometer and related to the concentration of the analyte.
Fig. 2-2: Color development
Absorbance = log (reference / sensor reading)
The DISPLAY screen of the CA6 displays the live Sensor reading, the recorded Reference reading, the
recorded sensor Reading, the Absorbance and the Blank (the absorbance through deionized water).
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