UV Visible Spectroscopy M.Pharm Notes PPT file, Pharmacy

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1. UV-Visible
Spectroscopy
Presented By- Saurabh
Dubey
M.Pharm
Bundelkhand University

2. Principle
.
UV Visible
Spectroscopy
Sample
Electronic
Transition
Absorbance
UV- Curve
(Ab Vs λ)
Spectral Shift

Bathochromic Shift- Red Shift [NIPER-2019, 22]
Shift towards longer wavelength
Energy Decrease

Hypsochromic Shift- Blue Shift
Shift towards shorter wavelength
Energy Increase

Hyperchromic Shift-
Intensity of absorption maxima increases (Emax Increases)

Hypochromic Shift-
Intensity of absorption maxima decreases(Emax decreases)

3. Introduction
Also known as Electronic Spectroscopy & Colorimetric
Study of Electronic Transition in Molecule
UV spectroscopy is concerned with the study of absorption of UV
radiation
❖ Range- UV spectroscopy-200-400 nm
❖ UV Visible spectroscopy-400-800 nm [NIPER JEE-2006,7]
In UV visible spectroscopy only the valence electrons absorb the
energy thereby the molecule undergoes transition from Ground state to
Excited state
The distinct type of electrons are involved in organic molecules these
are as follows Sigma (σ), pi (π) and n electrons

4. Theory
Any molecule has either n, π, σ or combination of these electrons
absorbing the characteristic radiation and undergoes transition from
Ground state to Higher Energy excited state.


Energy value order for transition- σ-σ* > η-σ* > π-π* > η-π*
1. σ-σ*- Required highest amount of energy
2. η-σ*- Lesser Energy than σ-σ*
3. π-π*- Less Energy Required (B-Bands, K-Bands), (Allowed Transition)
4. η-π*- Transition required Lowest Energy (R-Band), (Forbidden Transition)
Bonding (σ, π) &
non bonding orbital
(n)
Anti bonding
orbital (σ*, π*)

5. Laws
Beer's Lambert's Laws
When a beam of Monochromatic radiation is passed through the
Absorption medium the decrease in the intensity of radiation, When
increases the Concentration(c) or Thickness (Path length) (l) of the
Solution.
▪Ab has No Unit

6. Instrumentation

7. Instrumentation
Source of Light Trick- HDTMX
1.Hydrogen Deuterium (H2-D2) lamp (200-375 nm)
2.Tungsten Filament Lamp (375-800 nm) Commonly used, Similar to house bulb
3.Xenon arc lamp (160 to 2,000 nm)
4.Mercury arc lamp (250-350 nm)

Monochromator- It convert Polychromatic light into Monochromatic light
Entrance Slit-To get narrow source
Collimating lens- The radiation emitted by source is collimated (parallel) by lenses
Prism- A dispersive prism is used to break the radiation into its Constituent
radiation
Gratings- Diffracts light into several beams contain 1200-1400 grooves/nm
Refracting lens and Exit Slit- To fall on Sample cell

8. Instrumentation
Sample Container- Also k/a Cuvette is made up of Quartz and Some times
glass
Quartz is fused silica (SiO2); Consisting of Silica in amorphous (non
crystalline) form
Quartz has high working and melting temperatures

Detectors Trick- PMT PET Barrier
Device which convert light energy into electrical signals
1.Photomultiplier tube (Contain dynodes, Commonly used in UV) [MP DI-17,
BIHAR DI-23]
2.Barrier layer cell / Photovoltaic cell [NIPER JEE-2016]
3.Phototubes / Photo emissive tube
4.Photodiode array
5.Charge coupled device

9. Solvent and Solvent Effect
Solvents
Solvent should be Transparent for UV-Visible range (Not absorb UV
Visible Radiations)
Solvent should be free from any Particles
Always prepare a diluted sample Solution.
Not have any double bond in structure / UV Visible inactive
95% ethanol is most commonly used solvents [204 nm]
Eg:- Water[191 nm], Methanol[203 nm], Ethanol[204 nm]

10. Application
1- Determination of Concentration of Substance in a Solution
2- Determination of impurity or Contaminants
3- Determination of Highly Conjugated double bond (π-π*,η-π*) Compound
[GPAT-2013]
4- Qualitative and Quantitative analysis

11. Q1- The UV- Visible region in the electromagnetic spectrum of
radiation is [GATE-1990] [NIPER JEE- 2006, 2007]
a).200-400 nm b) 300-660 nm c) 400-800 nm d) 200-800 nm
Q2- If an organic compound does not absorb UV Visible radiation it
means compound does not contain [GPAT-2013]
a). Single bond b) Sigma bond c) Double bond d) Dative Bond
Q3- Detector used in UV Spectroscopy is [NIPER JEE-2016]
a).Photo voltaic Detector b) Pyroelectric c) Thermistor d) All of these
Q4- The Commonly used detector in UV spectroscopy is [MP DI-2017]
a). Photomultiplier b) Golay cell c) Both of the above d) None of these
Q5- Which of the following contain dynodes [BIHAR DI-2023]
a). Golay Detector b) Photovoltaic cell c) Photomultiplier d) MCT

12. Q6- Shifting of λ max toward red wavelength is termed as
[NIPER-2019]
a)Bathochromic shift b)Hypsochromic shift
c)Hyperchromic shift d)Hpochromic shift
Q7- Bathochromic Shift is also known as [NIPER- 2022]
a)Yellow shift b) Blue shift c) Green shift d)Red shift

Answer
Q1-c, Q2-c, Q3- a, Q4-a, Q5-c