UV-Visible Spectroscopy

Introduction:

           UV-Visible spectroscopy is a mature and well-established analytical technique used extensively in many industry sectors including Environmental Analysis, Pharmaceutical Testing, Food and Beverage Production etc.

          UV-Vis Spectroscopy is an analytical method used to measure the absorbance of ultra-violet or visible radiation through an analyte. The molecular absorption of the analyte corresponds to both excitation of valence electrons and excitation of electrons in different atomic orbitals. UV-Vis Spectroscopy is an effective technique for both qualitative and quantitative analysis of organic and inorganic compounds.

Principle:

            UV-Vis Spectroscopy is based on the Lambert-Beer principle which states that the absorbance of a solution (A) is directly proportional to its pathlength (l) and its concentration (c) when the wavelength of the incidence light remains fixed.

            The amount of light that is absorbed by the solution depends on the concentration, the path length of the light through the cuvette and how well the analyte the light absorbs at a certain wavelength. The transmittance I/I0 is an indication of the concentration of the analyte in the sample. I/I0 is defined as the transmittance (or transmission) T. If there is no absorption of the light passing through the solution, the transmittance is 100%.

Apparatus:

            The UV-Vis Spectrophotometer is the analytical instrument used for the UV-Vis spectroscopic analysis. Spectrophotometers are available in different configurations however most can be categorized into either single beam, split beam or double beam types depending on the design of their optical system. Such types of instrument comprise the following components in their constructions:

                        1. Light Source

2. Monochromator

3. Cell Compartment

4. Detector

5. Signal Processing System

This absorption spectroscopy uses electromagnetic radiation between 190 and 800 nm and is divided into two regions

1. UV (190–400 nm)- Deuterium lamp

2. Visible (400–900 nm) - Tungsten lamp

Because the absorption of UV or visible radiation by a molecule leads to transition among electronic energy levels of the molecule, it is also often called electronic spectroscopy.

UV-Visible Analysis is Suitable For,

            1. Analytes that can be dissolved in solvents like water, ethanol and hexane.

            2. The analyte need to absorb UV or Visible light.

            3. With UV /Vis we can do quantitative measurements a single analyte in solution(or more than one analytes om solution provided that do not interfere with each other).

Not Suitable For,

            1. Analytes that have a photochemical reaction at the wavelength range of interest.

            2. Partially dissolved, unclear or colloidal samples.

The UV-Vis spectrum shows the absorbance of one or more sample component in the cuvette when we scan through various wavelengths in the UV/Vis region of the electromagnetic spectrum.

Why UV-Vis analysis Used?

    1. This UV-Vis Spectroscopy method is simple, inexpensive and easy to handle.

    2. UV-Vis spectrometry is not only used for routine measurements. In laboratories UV-Vis detection can be used to monitor the separations in liquid chromatography.

    3. If a mixture is separated in a column the different compounds can be detected with a UV-Vis detector.

    4. UV-Vis detection is a relative cheap and easy detector compared to mass spectrometry (MS) detectors.

    5. It is applicable for many different not too complex samples. Therefore UV/Vis is used in a broad range of areas, mainly for routine measurements, for example in hospitals, petrochemical industry, food industry, water quality control laboratories. of pharmaceutical industries.