What is the Difference Between Polarimeter and Refractometer

The key difference between polarimeter and refractometer is that a polarimeter measures the angle of rotation, whereas a refractometer measures the index of refraction.

Polarimeter and refractometer are different analytical instruments that differ from each other according to the parameter they measure.

CONTENTS

1. Overview and Key Difference
2. What is a Polarimeter 
3. What is a Refractometer 
4. Polarimeter vs Refractometer in Tabular Form
5. Summary – Polarimeter vs Refractometer

What is a Polarimeter?

A polarimeter is an analytical instrument that is useful in measuring the angle of rotation that is caused by the passing of polarized light through an optically active substance. Typically, some chemical substances tend to be active and polarized, which makes the light rotate either to the left or right upon passing through these substances. The degree of rotation is known as the angle of rotation. We can learn information about the chiral properties of the sample by determining the direction and magnitude of the rotation.

When considering the principle of measurement of a polarimeter, we can measure the ratio, purity, and concentration of two enantiomers using this method. The plant of linear polarized light of enantiomers tends to indicate the ability to rotate light. Therefore, we name the enantiomers as optically active compounds, and this property is called optical rotation.

There are two Nicol prisms in a polarimeter. These two prisms act as the polarizer and the analyzer. A polarizer is fixed to one place while the analyzer can be rotated easily. The polarizer allows the light to enter and move in a single plane. Then the light becomes polarized. The analyzer allows this light to pass through it. If we rotate the analyzer, waves cannot pass through the right angle, and thus the field appears dark. There is a glass consisting of an optically active solution placed between the polarizer and the analyzer. Then the light can rotate through the plane of polarization to some angle. Next, we need to rotate the analyzer according to this particular angle, which allows us to determine the angle of rotation.

What is a Refractometer?

A refractometer is an analytical instrument that can determine the concentration of a particular substance in a liquid solution. It is a laboratory tool useful in the measurement of the index of refraction. We can calculate the index of refraction using the observed refraction angle and Snell’s law. Therefore, the index of refraction for the mixture allows us to determine the concentration using the rules of mixing, including the Gladstone-Dale relation and Lorentz-Lorenz equation.

We can find four major types of refractometers: traditional handheld refractometers, digital handheld refractometers, laboratory or Abbe refractometers, and inline process refractometers. Moreover, another type of refractometer is in use, which is known as the Rayleigh refractometer. It is useful in measuring the refractive indices of gases.

What is the Difference Between Polarimeter and Refractometer?

Polarimeter and refractometer are very important analytical instruments that have important uses in a laboratory. The key difference between polarimeter and refractometer is that a polarimeter measures the angle of rotation, whereas a refractometer measures the index of refraction.

The below infographic presents the differences between polarimeter and refractometer in tabular form for side by side comparison.

Summary – Polarimeter vs Refractometer

A polarimeter is an analytical instrument that is useful in measuring the angle of rotation that is caused by the passing of polarized light through an optically active substance. A refractometer is an analytical instrument that can determine the concentration of a particular substance in a liquid solution. The key difference between polarimeter and refractometer is that a polarimeter measures the angle of rotation, whereas a refractometer measures the index of refraction.

Reference:

1. Filmetrics, From, et al. “Refractometer – Definition and Applications.” AZoOptics.com, 5 June 2020.

Image Courtesy:

1. “Polarimeter (Optical rotation)” By Kaidor – This vector image includes elements that have been taken or adapted from this file: (CC BY-SA 3.0) via Commons Wikimedia
2. “2020 Refraktometr” By Jacek Halicki – Own work (CC BY-SA 4.0) via Commons Wikimedia