2. SPECTROSCOPY
Study of spectrum formed by interaction of matter with
radiant energy.
Spectroscopy is the branch of science that involves the
study of interaction of electromagnetic radiations with
atoms or molecules.
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3. UV/VISIBLE
SPECTROSCOPY:-
Uv-vis spectroscopy is also known as
electronic spectroscopy. In which the
amount of light absorbed at each
wavelength of Uv and visible regions
of electromagnetic spectrum is
measured. This absorption of
electromagnetic radiations by the
molecules leads to molecular
excitation.
4. ELECTROMAGNETIC SPECTRUM
The arrangement of all types of electromagnetic radiations in order of
their increasing wavelengths or decreasing frequencies is known as
complete electromagnetic spectrum.
5. PRINCIPLE
The absorption of energy by ground state atom in the
gaseous state forms the basis of atomic absorption
spectroscopy.
Spectrum is a graph of intensity of absorbed or emitted
radiation by sample verses frequency (ν) or wavelength
(λ).
A phenomenon of interaction of molecules with
ultraviolet and visible lights.
Absorption of photon results in electronic transition of a
molecule, and electrons are promoted from ground state
to higher electronic states.
6. Principle is based upon the electronic
transitions:
σ → σ* transition
π → π* transition
n → σ* transition
n → π* transition
7. σ → σ* transition
σ electron from orbital is excited to corresponding anti-
bonding orbital σ*.
Methane (CH4) has C-H bond only can undergo Sigma-
Sigma star transition and show absorbance maximum at
125 nm.
8. n → σ* transition
Saturated compounds containing atoms with lone pair of
electrons like O, N, S and halogens are capable of n →
σ* transition.
9. π → π* transition
π electron in a bonding orbital is excited to
corresponding anti-bonding orbital π*.
Compounds containing multiple bonds like alkenes,
alkynes, carbonyl, nitriles, aromatic compounds, etc
undergo π →π* transitions.
10. n → π* transition
An electron from non-bonding orbital is promoted to
anti-bonding π* orbital.
Compounds containing double bond involving hetero
atoms (C=O, C≡N, N=O) undergo such transitions.
11. INSTRUMENTATION
Following are the general components of atomic absorption
spectrometer:
Sources of Radiation (UV and Visible)
Wavelength selector (Monochromator)
Cuvette (sample and refrence container)
Detectors
Signal processor (amplifier) and read-out device.
12.
13. RA D IATION SOURCE
Visible source:
Tungston filament lamp
Range: 350-2500nm
The lifetime of a tungsten/halogen lamp is approximately
double that of an ordinary tungsten filament lamp.
14. WAVELENGTH SELECTOR
There are following components in every monochromators
namely:
Entrance slit
Dispersing device (prism of grating)
Focusing lens
Exit slit
15.
16. CUVETTE
The containers for the sample and reference
solution must be transparent to the radiation
which will pass through them. These cells are
also transparent in the visible region. Silicate
glasses can be used for the manufacture of
cuvettes for use between 350 and 2000 nm.
18. ABSORBANCE LAW’S
There are two absorbance laws, related to the principle of UV-vis
spectroscopy, helps us to define the relationship between the intensity of
visible UV radiation and the exact quantity of substance present. namely,
Beer law and Lambert law.
BEER LAW - Beer’s law stated that absorbance is proportional to the
concentrations of the material sample.
“The intensity of a beam of monochromatic light decreases exponentially
with increase in the concentration of absorbing species arithmetically”
19. Cont...
LAMBERT LAW- Lambert’s law stated that absorbance of a material is
directly proportional to its thickness (path length)
The rate of decrease of intensity of monochromatic light with the
thickness of medium is directly proportional to the intensity of
incident light.
On combining these two laws – for a given material sample path length
and concentration of the sample are directly proportional to the
absorbance of the light.
A prepositional to CL
A- Absorbance
C- Concentration
L – Parth length
20. APPLICATIONS
Detection of impurities in the sample.
Quantitative analysis
Qualitative analysis
Dissociation constants of acids and base
Chemical kinetics
Quantitative analysis of pharmaceutical analysis
Molecular weight determination.
A Unknown concentration of a solution can be
determined by UV – Vis spectroscopy
Manufacturing drugs
