2-1
Chapter 2 Function
2.1 Theory
The Model HALO RB-10 Spectrophotometer is designed for absorption analysis
of liquid, solid and gaseous samples in the ultraviolet and visible spectral
regions.
Measurements are based on the Lambert-Beer law, as shown in Figure 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
’ .
The initial intensity ‘I
0
’ and attenuated intensity ‘I
t
’ of monochromatic radiation,
follows equation (1).
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 Lambert-Beer law, ‘
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 (1/
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
essential for quantitative measurement.