Difference Between Single Beam and Double Beam Spectrophotometer

The key difference between single beam and double beam spectrophotometer is that in single beam spectrophotometer, all the light waves pass through the sample whereas, in double beam spectrophotometer, the light beam splits into two parts and only one part passes through the sample. Spectrophotometers are analytical instruments used to quantify the analytes in a given sample using a light beam. Therefore, this technique measures the absorption of light by the sample.

CONTENTS

1. Overview and Key Difference
2. What is Single Beam Spectrophotometer
3. What is Double Beam Spectrophotometer
4. Side by Side Comparison – Single Beam vs Double Beam Spectrophotometer in Tabular Form
5. Summary

What is Single Beam Spectrophotometer?

Single beam spectrophotometer is an analytical instrument in which all the light waves coming from the light source passes through the sample. Therefore, the measurements are taken as the intensity of light before and after the light pass through the sample. These single beam spectrophotometers are more compact and optically simpler than double beam spectrophotometers. And also these instruments are less expensive.

The sensitivity of detection of the light beam after it passes through the sample is high since it uses a non-split light beam (therefore, high energy exists throughout). Single beam spectrophotometers are available in analysis at visible and ultraviolet wavelength ranges.

A single beam spectrophotometer measures the concentration of an analyte in a sample by measuring the amount of light absorbed by that analyte. Here, the Beer Lambert Law comes into operation. This law states that the concentration of an analyte is directly proportional to the absorbance.

What is Double Beam Spectrophotometer?

Double beam spectrophotometer is an analytical instrument in which the light beam coming from the light source splits into two fractions. One fraction acts as the reference (the reference beam) while the other fraction passes through the sample (sample beam). As a result, the reference beam does not pass through the sample.

The sample beam can measure the absorbance of the sample. The reference beam can measure the absorption (the sample beam can be compared with the reference beam). Therefore, the absorption is the ratio between the sample beam (after passing through the sample) and a reference beam. A spectrophotometer has a monochromator that isolates the desired wavelengths from a light beam. The reference beam and sample beam recombine before moving to the monochromator. Consequently, this avoids or compensate the electronic and mechanical effects on both sample and reference beams, equally.

What is the Difference Between Single Beam and Double Beam Spectrophotometer?

Summary – Single Beam vs Double Beam Spectrophotometer

A spectrophotometer is an instrument that analyzes the components of a solution by observing the capability to absorb light. There are two main types of spectrophotometers; single beam and double beam spectrophotometer. The difference between single beam and double beam spectrophotometer is that, in single beam spectrophotometer, all the light waves pass through the sample whereas, in double beam spectrophotometer, the light beam splits into two parts and only one part passes through the sample.

Reference:

1. “Single-Beam Spectrophotometers.” Biocompare. Available here  
2. “Comparison between Single Beam and Double Beam Atomic Absorption Spectrometer Systems.” Lab-Training.com, 22 July 2015. Available here 

Image Courtesy:

1.’Spetrophotometer-en’By GYassineMrabetTalk- Own work, (CC BY-SA 4.0) via Commons Wikimedia
2.’Simplified UV-vis diagram’ By Sobarwiki- Own work, (Public Domain) via Commons Wikimedia