This document provides an overview of UV-Visible spectroscopy. It discusses the basic principles, components, and types of UV-Visible spectrophotometers. The key components include a light source, monochromator, cuvettes to hold samples, and detectors. It also describes the principles of absorption spectroscopy and how double-beam spectrophotometers work by splitting the light source into reference and sample beams to improve accuracy. UV-Visible spectroscopy is a common technique for quantitative analysis that measures how light is absorbed by molecules at different wavelengths.

1. CDLU SIRSA
DEP. OF ENERGY AND
ENVIRONMENTAL
SCIENCE
PRESENTED TO :
• UV VISIBLE SPECTROSCOPY
PRESENTED BY :
RAJESH KUMAR
MSC 2 SEM

2. INTRODUCTION
PRINCIPLE
COMPONENTS
TYPES
REFRANCES

3. INTRODUCTION
 Spectrophotometry is commonly applied physicochemical technique, which is
notable for its sensitivity and precision.
 This technique is used to measures light intensity as a function of
wavelength.
 Popularity of the spectrophotometric technique are the instrument is easy to
operate and commonly available.
 The primary advantage of spectrophotometric method is that they determine
minute quantities of substances.

4. • Spectrophotometry in the visible region of electromagnetic spectrum generally
considered to range from 400 nm to 800 nm, is called colorimetry.
• Colorimetry is a technique of analysis based on relating the color intensity of the
unknown with that of standard solution.
• UV wavelength 200 nm to 400 nm.
• In spectrophotometric analysis, the intensity of radiation, transmitted by an absorbing
medium placed between the light source and the detector is measured as a function of
wavelength.

5. Electromagnetic Radiation
• At times light appears to behave like a wave; at other times it behaves as though it were
composed of small particles. While we now understand the “wave–particle duality” of all
matter,
• Light waves can be represented as oscillating perpendicular electric and magnetic fields.
• We can easily and accurately measure the wavelength 𝛌 defined as the crest-to-crest
distance between two successive maxima.
• The amplitude of the wave is defined as the maximum of the vector from the origin to a
point displacement of the oscillation.
• Light of only one wavelength is called monochromatic light. Light consists of more than
one wavelength is called polychromatic light.
• White light is an example of polychromatic light.

6. • The frequency of a wave is the number of crests passing a fixed point per second.
• The common unit of frequency is the hertz (Hz)
• The wavelength of light, λ is related to its frequency, ν
c = λѵ (Eq 1)
( c is the speed of light in a vacuum, ν is the frequency of the light, λ is the
wavelength )
• In some cases it is more convenient to consider light as a stream of particles
• Particles of light photons.
• The energy of a photon is related to the frequency of light
Ε = hν (Eq 2)
( E is the energy, h is constant, ν is the frequency )
• Electromagnetic radiation ranges from very low energy radiation, like radio waves and
microwaves, to very high energy radiation, like X-rays.

7. LAWS OF PHOTOMETRY
LAWS OF PHOTOMETRY: When a beam of electromagnetic affects on matter several
types of interactions such as reflection, refraction, diffraction, interference, absorption
etc., may occur. Of these interactions, absorption in which certain frequencies are
selectively removed by matter is of unique importance. The energy thus absorbed is
transferred to atoms or molecules in matter. As a result, these atoms or molecules in the
ground state are excited.

8. • The radiant power P of a beam of light is defined as the energy of the
beam per second per unit area.
• A related quantity is the intensity I which is the power per unit solid.
• When light passes through an absorbing sample, the intensity of the light
emerging from the sample is decreased.
• Intensity of a beam of monochromatic radiation is Io.
• The emerging light beam has an intensity equal to I , where Io = I. If no
radiation is absorbed by the sample,
• If any amount of radiation is absorbed, I < Io . The transmittance T is
defined as the ratio of I to Io.
• T =𝐼/𝐼o

9. Components of spectrophotometer
An instrument employed to measure the amount of light that a sample
absorbs.
Consists of two instruments:
• A spectrometer for producing light of any selected color (wavelength)
• A photometer for measuring the intensity of light

10. Light source :
Visible spectrophotometer
Contains a tungsten lamp.
Ultraviolet spectrophotometer
Contains a deuterium lamp that produces light in the UV light part of the
spectrum.
Xenon flash lamps
Xenon flash lamps have several advantages as the following :
1)Their range between ( 190nm - 1000 nm)
2) Emit both UV and visible wavelengths
3) Long life
4) Do not heat up the instrument
5) Reduce warm up time

11. Monochromator
• A Monochromator consists of a dispersion element, an entrance slit and an
exit slit, plus lenses and mirrors for collimating and focusing the beam of
radiation. :
• The function of the dispersion element is to spread out in space, or disperse,
the radiation falling on it according to wavelength. The two most common
types of dispersion elements are prisms and gratings. The entrance slit allows
light from the source to fall on the dispersion element. The dispersed light falls
on the exit slit of the Monochromator. The function of the exit slit is to
permit only a very narrow band of light to pass through the sample to detector

12. • Prism
Prisms are used to disperse Visible, and UV radiation. If a parallel beam of radiation
falls on a prism , the radiation of two different wavelength will be bent through
different angles. The most common prisms are constructed of quartz for the UV
region, silicate glass for the visible and near-IR region, and NaCl or KBr for the IR
region
Filter
Filters separate different parts of the electromagnetic spectrum by absorbing or
reflecting certain wavelengths and transmitting other wavelengths. Absorption filters
are glass substrates containing absorbing species that absorb certain wavelength.
Interference filters are made of multiple dielectric thin films on a substrate. They
use interference to selectively transmit or reflect a certain range of wavelengths.

13. • Diffraction gratings
Diffraction grating is an optical component with a regular pattern, which splits
(diffracts) light into several beams travelling in different directions. The directions of
these beams depend on the spacing of the grating and the wavelength of the light so
that the grating acts as a dispersive element. It consist 500 to 5000 grooves/mm for
UV or visible region. 50 to 200 grooves /mm for IR region.

14. Cuvettes (sample)
• A cuvette is a kind of cell (usually a small tube) sealed at one end, made of
Plastic, glass or optical grade quartz and designed to hold samples for
spectroscopic experiments.

15. Detectors
• Any photosensitive device can be used as a detector of radiant energy .The
photocell and phototube are the simplest photodetectors, producing current
proportional to the intensity of the light striking Them .
The most common detector in use is the PMT. The operation of the PMT was
described earlier in this chapter. Because the signal is small due to the low
concentrations of analyte used, the PMT is often cooled to sub ambient
temperature to reduce noise. The limitation of the PMT is that it is a single
wavelength detector

16. Types of spectrophotometer
1) Single-Beam Optics
2) Double-Beam Optics
Single-Beam Optics
Single-beam are used for all spectroscopic emission
methods. In emission procedures the sample is put where the source is located. In
spectroscopic absorption studies the intensity of radiation before and after passing
through the sample must be measured. When single-beam optics are used, any
variation in the intensity of the source while measurements are being made may lead
to analytical errors.

17. Double-Beam Optics
The double-beam system is used for spectroscopic
absorption studies. The individual components of the system have the same
function as in the single-beam system, with one very important difference. The
radiation from the source is split into two beams of approximately equal
intensity using a beam splitter. One beam is termed the reference beam; the
second beam, which passes through the sample, is called the sample beam. The
two beams are then recombined and pass through the monochromator and slit
systems to the detector.

18. REFRANCES
1) UNDERGRADUATE INSTRUMENTAL ANALYSIS Sixth
Edition .James W. Robinson
2) slide share
3) class notes
4) google.com