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Dual-Beam uv-vis Spectrophotometer

Introduction

In single-beam uv-vis absorption spectroscopy, obtaining a spectrum requires manually measuring the transmittance (see the Beer-Lambert Law) of the sample and solvent at each wavelength. The double-beam design greatly simplifies this process by measuring the transmittance of the sample and solvent simultaneously. The detection electronics can then manipulate the measurements to give the absorbance.


Instrumentation

The dual-beam design greatly simplifies this process by simultaneously measuring P and Po of the sample and reference cells, respectively. Most spectrometers use a mirrored rotating chopper wheel to alternately direct the light beam through the sample and reference cells. The detection electronics or software program can then manipulate the P and Po values as the wavelength scans to produce the spectrum of absorbance or transmittance as a function of wavelength.

Schematic of a dual-beam uv-vis spectrophotometer

Pictures of Lambda 3A and 4B dual-beam uv-vis spectrophotometers

Larger picture of the Lambda 3a spectrophotometer
Close-up of the control panel / Close-up of the sample compartment

Pictures of a Hitachi dual-beam uv-vis spectrophotometer

Larger picture / Picture of the sample compartment

Picture of the sample cells


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