Ultraviolet-visible (UV-Vis) spectrophotometry is a technique used to measure light absorbance across the ultraviolet and visible ranges of the electromagnetic spectrum. When incident light strikes matter it can either be absorbed, reflected, or transmitted.

1. UV- VISIBLE
SPECTROSCOPY
- VARNIT CHAUHAN
17/IBT/042
Gautam Buddha University

2. WHAT IS SPECTROSCOPY?
Branch of science that deals with the study of interaction of matter with light.
OR
Branch of science that deals with the study of interaction of electromagnetic radiation with
matter.
Types:
❏ Absorption - UV, IR, NMR, etc
❏ Emission - Fluorimetry, Flame photometry, etc
Study:
❏ Atomic - AAS, Flame photometry, etc.
❏ Molecular - UV, IR, etc.

3. ELECTROMAGNETIC SPECTRUM
The entire distribution of
electromagnetic radiation
according to frequency or
wavelength

4. UV- VISIBLE SPECTROSCOPY
❏ UV visible spectroscopy covers the wavelength 150 to 800 nanometers.
❏ Valence electrons absorb the energy thereby molecules undergoes transition from ground
state to excited state.
❏ This absorption is characteristic and depends on the nature of electrons present.

5. THEORY
If a particular wavelength of UV or Visible radiation can be isolated from the source and
passed through a sample which can ABSORB some of the radiation then the TRANSMITTED
light intensity (I t ) will less than the INCIDENT light intensity (I o).
The amount of light transmitted with respect to the incident light is called
TRANSMITTANCE (T) ie.,
Sample can absorb all or none of the incident light and therefore transmittance often quoted
as a percentage eg.,

6. LAWS INVOLVED
There are two very important basic laws and a third one which is a combination of the two.
❏ LAMBERT'S LAW – ABSORBANCE (A) proportional to the PATHLENGTH (l) of the
absorbing medium.
❏ BEER'S LAW - ABSORBANCE (A) proportional to the CONCENTRATION (c) of the
sample.
❏ BEER- LAMBERT LAW - ABSORBANCE (A) proportional to c x l
A 𝛼 c l
A = Ecl
The constant E is called the MOLAR EXTINCTION COEFFICIENT

7. UV SPECTROPHOTOMETER
A spectrophotometer is an analytical instrument used to quantitatively measure the
transmission or reflection of visible light, UV light or infrared light.
Component of Spectrophotometer:
❏ Radiation source: Hydrogen- discharge lamp is the most commonly used source of
radiation in the UV region. A deuterium- discharge lamp is used in its place when more
intensity is desired.

8. ❏ Monochromator: It disperses the radiations obtained from the source into their separate
wavelengths.
❏ Prism
❏ Grating made up of quartz
❏ Detectors: These have photocells or photomultiplier tubes which generate voltage
proportional to the radiation energy that strikes them.
❏ Amplifier : The spectrometer has balancing electronic amplifier which subtracts the
absorption of the solvent from that of the solution electronically.

9. ❏ Recorder : It automatically records the spectrum as a plot of wavelengths of absorbed
radiations against absorbance or molar absorptivity

10. UV SPECTROPHOTOMETER
Types :
❏ Single Beam Spectrophotometer
❏ Double Beam Spectrophotometer

11. APPLICATION
❏ Qualitative analysis
❏ Quantitative analysis
❏ Detection of Impurities
❏ Detection of functional groups
❏ Detection of molecular weight
❏ Structural elucidation

12. ACKNOWLEDGEMENT
❏ University of Lincoln
❏ Sciencedirect
❏ Pubmed
❏ Slideshare