Electro-Chemical Devices (ECD) CA6 Hardness Analyzer - Manual (Page 18)

2.0 INTRODUCTION – Analyzer Description
This manual provides general information regarding the principles of
operation, the proper installation and operation of the CA-6 Analyzer.
The Model CA-6 is an on-line sequential sampling analyzer (a sequence of
sampling, analysis and result processing), using colorimetric methods.
The analyzer is assembled with two separated sections with two lockable
doors. The bottom section is the LIQUIDS section. It includes all of the
components involved in the flow, mixing and reaction stages of the sample
and reagents (sampling pump, colorimetric reaction cell, reagents micro
pumps,..). Numerous analysis configurations can be programmed,
depending on accessories and of the number of micro pumps mounted in
the Liquid Section. The top section is the ELECTRICAL enclosure. It includes
the main power supply, the controller PCB assembly and the touch screen
interface.
2.1 Applications
The measurement is a colorimetric analysis using an LED light source and a heated colorimetric cell
designed for measuring trace amounts of analyte in water.
2.2 Working principle: Lambert-Beer law
A colorimetric determination is based on the color formation of a solution after the addition of reagents.
The Absorbance of the solution is measured at a specific wavelength and is related to sample
concentration according to 'Beer's law'.
Lambert–Beer law is an empirical relationship relating the absorption of light to the properties of the
material through which the light is travelling.
The law states there is a logarithmic dependence between the transmission (transmissivity), T, of light
through a substance and the product of the absorption coefficient of the substance, α, and the distance
the light travels through the material (i.e. the path length), ℓ.
The transmission (or transmissivity) is expressed: T = I
1
/ I
0
Absorbance for liquids is defined as the negative logarithm of the transmittance:
A= - log
10
T =log
10
1/T =log
10
I
0
/I
1
I
0
: light intensity through the sample before colorimetric reaction
I
1
: light intensity through the sample after colorimetric reaction
In most cases the absorbance has a linear correlation to sample
concentration so a calibration line just requires a zero and span value.
(Zero analyte concentration and the maximum expected
concentration) are needed. Multiple analysis of the standard are
averaged to gain a reliable calibration line. (See section 8.7)
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