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UV-VISIBLE SPECTROSCOPY: AN OVERVIEW

ABOUT AUTHORS:
Kambham Venkateswarlu1*, N.Devanna2, Haritha Arikeri3, M.Shahinaz Farihath4
1,4M.Pharm Scholar, Department Of Pharmaceutics,
2Director Of JNTUA-Otri,
3M.Pharm Scholar, Department Of Pharmaceutical Analysis
JNTUA-Oil Technological Research Institute,
Beside Collector Office, Anantapur, Anantapur District, Andhra Pradesh, India. Pin Code: 515001
*k.v.reddy9441701016@gmail.com

ABSTRACT:
Spectroscopy is often used in physical and analytical chemistry for the identification of substances through the spectrum emitted from or absorbed by them. Spectroscopy is also heavily used in astronomy and remote sensing. Most large telescopes have spectrometers, which are used either to measure the chemical composition and physical properties of astronomical objects or to measure their velocities from the Doppler Shift of their spectral lines.
UV-Visible spectroscopy is a form of Absorption spectroscopy. Absorption spectroscopy in the UV-Visible region is to be one of the oldest and most frequently employed technique in pharmaceutical analysis for qualitative, quantitative and structural analysis of a substance in solution. The substance is analyzed by studying the spectrum produced by it due to absorption of certain wavelengths of UV-Visible light.
Spectroscopically, visible light behaves in a similar way as UV light. Hence, the techniques of UV spectroscopy and Visible spectroscopy are studied together.

REFERENCE ID: PHARMATUTOR-ART-2078

1. INTRODUCTION:
The spectrophotometer has well been called the workhorse of the modern laboratory. In particular, ultraviolet andvisible spectrophotometer is the method of choice in most laboratories concerned with the identification and measurement of organic and inorganic compounds in a wide range of products and processes - in nucleic acids and proteins, foodstuffs, pharmaceuticals and fertilizers, in mineral oils and in paint. In every branch of molecular biology, medicine and the life sciences, the spectrophotometer is an essential aid to both research and routine control. Modern spectrophotometers are quick, accurate and reliable and make only small demands on the time and skills of the operator. However, the user who wants to optimize the functions of his instrument and to be able to monitor its performance in critical areas will need to understand the elementary physics of the absorption process as well as the basic elements of spectrophotometer design.

2. SPECTROSCOPY

Definition:
Spectroscopy is defined as the study of interaction of EMR with matter. It is used for analysis of wide range of samples.

Spectrum:
A plot of the response as a function of wavelength or more commonly frequency is referred to as a spectrum.

Spectrometry:
It is the measurement of these responses and an instrument which performs such measurements is a spectrometer or spectrograph,

Common types:

•      Fluorescence spectroscopy

•      X-ray spectroscopy and crystallography

•      Flame spectroscopy

1- Atomic emission spectroscopy

2- Atomic absorption spectroscopy

3- Atomic fluorescence spectroscopy

•      Plasma emission spectroscopy

•      Spark or arc emission spectroscopy

•      UV/VIS spectroscopy

•      IR spectroscopy

•      Raman spectroscopy

•      NMR spectroscopy

•      Photo thermal spectroscopy

•      Thermal infra-red spectroscopy

•      Mass Spectroscopy

3. UV- VISIBLE SPECTROSCOPY:
Spectroscopically, visible light behaves in a similar way as UV light.  Hence, the techniques of UV spectroscopy and Visible  spectroscopy are studied together.

The UV-Visible spectroscopy is concerned with the UV & Visible  regions of the EMR which ranges between 200-800nm.

UV wavelength range is 200-400 nm.

Visible region wavelength range is 400-800 nm.

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4. PRINCIPLE:
The principle involved in UV-Visible spectroscopy is absorption spectroscopy. The principle of UV-Visible spectroscopy is based on the fundamental law of absorption called Beer-Lambert’s law. This law governs the absorption of radiation by an absorbing medium (dilute solution).

Beer’s law:
According to Beer’s law, when a beam of monochromatic radiation passes through an absorbing medium, the intensity radiation decreases exponentially with an increase in the concentration of the absorbing medium.

In other words, absorbance is directly proportional to the concentration of the absorbing substance.

Lambert’s law:
According to Lambert’s law, the rate of decrease in the intensity of the radiation (I) with the thickness of the medium (t) is directly proportional to the intensity of the incident light.

5. Instrumentation:
The different components present in the spectrophotometer are as follows:

5.1. Source of light:

Tungsten lamp:It can offer sufficient intensity.

Carbon arc lamp: It can provide high intensity light.

5.2. Filters and Monochromators:
These can convert the polychromatic light into monochromatic light.

Filters:

These are two types:

1.     Absorption filters

2.     Interference filters

Monochromators:

1.     Prism type

2.     Grating type

Prism types:

These two types:

a.     Dispersive type of prisms

b.     Littrow type of prisma

Grating types:

a.     Diffraction grating

b.     Transmission grating

5.3. Sample cells:
These are also called as ‘cuvettes.’

Sample volume:
Small volume à<0.5 ml

Large volume à5-10 ml

Shape of cell: Cylindrical or rectangular cells

Material:
For visible region colour corrected fused glass
For UV region cells which are made up with quartz.

5.4. Detectors:
In UV/Visible spectrophotometers these can be called as photometric detectors.

Types:
1. Photo voltaic cell or barrier layer cell
2. Photo emissive cells or photo tubes
3. Photo multiplier tubes

6. Conclusion:
By using this equipment can determine the lambda max, which is unique for each and every compound.

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