13
SECTION 3
– Theory and Practice of Spectroscopy Measurements
3.1
THEORY OF SPECTROSCOPY MEASUREMENT
UV-visible spectroscopy is the measurement of the absorbance of light at a specific wavelength in a
sample. This is used to identify the presence and concentration of molecular entities within the
sample. The Beer-Lambert law is used to relate the absorption of light to the properties of the sample
through which the light is travelling through. The Beer-Lambert law states that:
A
is the absorbance
is the molar absorption coefficient (l mol
-1
cm
-1
)
c
is the concentration (mol l
-1
)
l
is the path length (cm)
This law shows that absorbance is linear to concentration but this is only true for low concentrations.
For absorbance levels above 3 the concentration starts to move away from the linear relationship.
Transmittance is the proportion of the light which passes through the sample:
Therefore:
Absorbance is inversely related to transmittance:
l
I
0
I
t
Where:
I
o
is the incident light
I
t
is the transmitted light
l
is the path length
Summary of Contents for 7300
Page 1: ...Operating Manual 730 005 REV D 08 14 Model 7300 and 7305 Spectrophotometer...
Page 2: ...2...
Page 56: ...56 SECTION 11 Declaration of Conformity...
Page 57: ...57...
