Uv visibleSpectroscopy

2. What is the
spectroscopy ?
➢ Spectroscopy is branch science which is deal
with study of the interaction between
radiation and matter as a function
of wavelength (λ).
➢ In other words, it is a science that deal with
examination or evaluation of spectrum & how
that interacts with matter.
➢ Atoms and molecules may absorb and/or emit
EMR.

4. ❖ UV-visible absorption spectroscopy
1. UV-visible Spectroscopy is type of absorption
spectroscopy that involves study of the interaction of
UV-Visible radiation with molecule.
2. It is the measurement of attenuation of beam of light
after it passes through sample or after reflection from
a sample surface.
3. Measurement absorption or transmittance
4. Absorption of light in the UV/Visible part of the
spectrum (210 – 700 nm).

5. ★ Wavelength in UV
and visible region is
expressed in
nanometers or in
angstroms.
Absorption is
expressed in terms
of wave number (cm-
1).

6. Molecules containing π-electrons or non-bonding electrons (n-electrons)
can absorb energy in the form of ultraviolet or visible light to excite these
electrons to higher anti-bonding molecular orbitals.[2] The more easily
excited the electrons (i.e. lower energy gap between the HOMO and the
LUMO), the longer the wavelength of light it can absorb. There are four
possible types of transitions (π–π*, n–π*, σ–σ*, and n–σ*), and they can
be ordered as follows: σ–σ* > n–σ* > π–π* > n–π*

7. ❏ INSTRUMENTATION
Instruments for measuring the absorption of U.V. or visible radiation are
made up of the following components;
1. Sources (UV and visible)
2. filter or monochromator
3. Sample containers or sample cells
4. Detector

8. ❏ Principle of UV-visible spectroscopy
UV spectroscopy obeys the Beer-Lambert law,according to the Beer-Lambert Law
the absorbance is
proportional to the concentration of the substance in
solution and as a result UV-visible spectroscopy can also
be used to measure the concentration of a sample.
The Beer-Lambert Law can be expressed in the form of
A = log (I0/I) = Ecl
Where, A = absorbance
I0 = intensity of light incident upon sample cell
I = intensity of light leaving sample cell
C = molar concentration of solute
L = length of sample cell (cm.)
E = molar absorptivity
From the Beer-Lambert law it is clear that greater the number of molecules capable
of absorbing light of a given wavelength, the greater the extent of light absorption.

9. ❏ Application of uv-visible spectroscopy
1. Detection of Impurities.
2. Structure elucidation of organic compounds.
3. Quantitative analysis.
4. Qualitative analysis
5. Chemical kinetics.
6. Quantitative analysis of pharmaceutical substances.
7. Molecular weight determination

10. Thank you