What’s In It? Find Out with Refractometers, the Most Versatile of Lab Equipment

Quick quiz: What item of lab equipment can be found in a mechanic’s toolbox, a winery, and even a gemologist’s desk? This resourceful device can also be used by labs to conduct drug testing, but is most often used in the food and beverage industry. Of course, it’s the refractometer, which is so versatile it can test everything from battery acid to the authenticity of emeralds. Both home beer brewers and aquarium keepers rely on a refractometer for very different purposes.

The refractometer requires only a few drops of liquid to measure concentrations of aqueous solutions. Solutions have different refractive indexes depending on their concentration and a refractometer can measure the purity of the composition of the solution. For example, a Brix refractometer can determine the amount of sucrose in fruit juice for quality analysis. Different types of refractometers can measure gases and translucent solids. Most models feature Automatic Temperature Compensation (ATC), which is a built-in measure that ensures accuracy.

How They Work

When light enters a liquid it changes direction; this is called refraction. Refractometers measure the degree to which the light changes direction, called the angle of refraction. A refractometer takes the refraction angles and correlates them to refractive index (nD) values that have been established. Using these standard values, you can determine the concentrations of solutions.

The prism in the refractometer has a greater refractive index than the solution. Measurements are read at the point where the prism and solution meet. With a low concentration solution, the refractive index of the prism is much greater than that of the sample, creating a large refraction angle and a low reading. The reverse would happen with a high concentration solution.

For types of refractometers, read more