Ultraviolet–visible spectroscopy

Introduction

Ultraviolet–visible spectroscopy (UV-Vis or UV/Vis) refers to the absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent (near-UV and near-infrared (NIR)) ranges. The absorption or reflectance in the visible range directly affects the perceived color of the chemicals involved. In this region of the electromagnetic spectrum, molecules undergo electronic transitions. This technique is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the excited state to the ground state, while absorption measures transitions from the ground state to the excited state.

Basic Principles

Ultraviolet-visible spectroscopy involves the spectroscopy of photons (UV and visible light). It uses light in the visible and adjacent near-UV and near-infrared (NIR) ranges. In this method, a beam of light is passed through a sample (or the sample is immersed in light). The light transmitted is measured and the absorbed light is correlated with concentration.

The UV-Vis spectroscopy works on the principle of absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region. This means it uses light in the visible and adjacent (near-UV and near-infrared (NIR)) ranges. The absorption or reflectance in the visible range directly affects the perceived color of the chemicals involved.

Applications

Ultraviolet-visible spectroscopy is widely used in analytical chemistry for the quantitative determination of different analytes, such as transition metal ions, highly conjugated organic compounds, and certain biological macromolecules. UV/Vis spectroscopy is routinely used in analytical chemistry for the quantitative determination of different analytes, such as transition metal ions, highly conjugated organic compounds, and biological macromolecules.

Spectroscopic analysis is commonly carried out in solutions but solids and gases may also be studied. Solutions of transition metal ions can be colored (i.e., absorb visible light) because d electrons within the metal atoms can be excited from one electronic state to another. The color of metal ion solutions is strongly affected by the presence of other species, such as certain anions or ligands.

Instrumentation

Modern instruments are capable of measuring UV-Vis absorbance in both single-wavelength mode (i.e., fixed wavelength) and scanning mode. In single-wavelength mode, the wavelength of light passing through the sample cell does not change during the analysis. In scanning mode, the spectrometer varies the wavelength of light passing through the sample cell. This is useful for scanning the entire absorbance spectrum of a sample, or for monitoring the absorbance at a single wavelength as a function of time.

See Also

General Spectroscopy Infrared Spectroscopy Mass Spectrometry