2-1
Chapter 2 Function
2.1 Application
The HALO DB-20 Spectrophotometer is designed for absorption analyses of
liquid, solid and gaseous samples in ultraviolet and visible spectral regions.
In this scheme (Fig.2-1), a monochromatic beam with intensity ‘I
0
’ travels
through a liquid phase having concentration ‘c’ and path length ‘l’ , which
results in the intensity of monochromatic radiation decreasing to ‘I
t
’.
With respect to the initial intensity ‘I
0
’ and attenuated intensity ‘I
t
’ of
monochromatic radiation, the following equation (1) can be set up.
I
t
/I
0
= 10
-ε·c·l
=τ……………………………………………………….(1)
Where, ‘ε’ is a constant known as absorptivity, which varies depending on the
sample.
Equation (1) represents the statement of Lambert – Beer law, and ‘τ’ indicates
transmittance which is often expressed as a percentage, i.e. ‘τ× 100 = T’
(percent transmittance or %T).
Also, the common logarithm of inverse transmittance can be expressed as
follows:
Log (l/
τ) = ε·c·l = E …………………………………………………..(2)
Where ‘E’ is called absorbance (abbreviated as Abs).
Absorbance ‘E’ is proportional to concentration ‘c’ and is a unit of measurement
indispensable for quantitative determination.
Fig.2-1 Spectrophotometry Principle Scheme
To Next Page
Loading...
