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3 Jul 2017
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What Do Single And Double Beam Spectrophotometers Do?

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Posted By Leslie W.

A single and double beam spectrophotometer is an instrument which is designed to measure light by wavelength distribution.

There are a wide variety of different sizes and styles of spectrophotometers both single and dual beam, with their size and configuration largely dependent on the specific applications for which they are designed. A single beam instrument is used to measure the intensity of a beam of light before and then after the addition of a sample and uses a light source, a prism and a photocell as well as a sample holder for the material being analyzed by means of spectrophotometry.

Spectrophotometer single beam or double beam models offer the ability to control the wavelength and intensity of the light source. The results provided by these instruments are in the form of voltage fluctuations which are the light energy received by the photo cell into the form of electrical energy, which is then displayed and/or recorded on a connected computer for further analysis.

By contrast, spectrophotometers which are designed as double beam instruments gather data from the difference in light intensity of two beams of light. One beam's path contains a reference sample with known properties, the other containing the sample being tested. A spectrophotometer, single beam or double suitability for a given application depends on the sample to be tested and the demands of the application. For some purposes, one instrument is a better choice than the other.

The dynamic range of a single beam instrument tends to be larger and the instrument itself more compact as well as simpler in optical terms, which make these spectrophotometers easier to maintain and slightly less costly to operate, generally speaking.

Double beam models have their own set of advantages. Since these instruments are used with a reference sample, they do not typically need to be zeroed in between taking readings. These instruments also offer somewhat easier operation and the results tend to be more reproducible. However, the same feature (namely, it's complexity compared to a spectrophotometer single beam instrument) which lend it its greatest strengths are also the source of its weaknesses. A double beam spectrophotometer is more costly to purchase and maintain and slightly more costly to operate than a single beam instrument as well.

Both types of instrument are used to determine some of the physical properties of the sample being tested by providing information about the amount of light absorbed by the sample and at which wavelengths, data which can reveal much about the sample's characteristics.

Modern spectrophotometry techniques are of course done in conjunction with software which is designed to assist in interpreting the information yielded by the spectrophotometer. Single or double beam, this part of the analytical process is much the same. The data is uploaded to a computer for reporting, analysis and manipulation including plotting the information to a grid, conversion of transmittance data to absorbency, baseline correction and other procedures which allow researchers to learn more about the sample.

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