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Single-Beam UV-Vis Spectrophotometer

Introduction

Single-Beam spectrophotometers are often sufficient for making quantitative absorption measurements in the UV-Vis spectral region. The concentration of an analyte in solution can be determined by measuring the absorbance at a single wavelength and applying the Beer-Lambert Law.


Instrumentation

General aspects of UV-Vis spectrophotometers are given in the introductory document on UV-Vis spectroscopy. Single-beam spectrophotometers can utilize a fixed wavelength light source or a continuous source. The simplest instruments use a single-wavelength light source, such as a light-emitting diode (LED), a sample container, and a photodiode detector. Instruments with a continuous source have a dispersing element and aperture or slit to select a single wavelength before the light passes through the sample cell. (see schematic below).

In either type of single-beam instrument, the instrument is calibrated with a reference cell containing only solvent to determine the Po value necessary for an absorbance measurement.

Schematic of a wavelength-selectable, single-beam UV-Vis spectrophotometer
spectrometer

Pictures of single beam UV-Vis spectrophotometers (Spectronic 20 and 20D)

Larger picture of the Spectronic 20D with labels.


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