Refractometry (Refractometry)

Refractometry is an optical technique, primarily used to determine the concentration of a solute dissolved in liquid, by measuring the refractive index of the sample. Refractometry is also used for purity investigation of diamonds and forensic analysis of glass.

Refractometry

Refractometry is an optical technique, primarily used to determine the concentration of a solute dissolved in liquid, based on the refraction of light through the solution. The refractive index of a solution varies with the concentration of the solute, attributable to interactions between the transmitted light and solute molecules, as well as optical density effects. Refractive index depends on the wavelength of the incident beam and usually the incident beam has a wavelength of 589 nm, which is the Sodium ‘D’ line. The refractive index changes with temperature of the medium, with the rate of change depending on the medium. Refractometry is also used for purity investigation of diamonds and forensic analysis of glass.

The Refractometry technique involves measuring the refractive index of a test sample and comparing it with calibration standards, to obtain the solute concentration. The measurement is performed in a Refractometer.

Refractometers use the critical angle at which total internal reflection occurs, to measure the refractive index of a sample. There are four main types of fluid refractometers: traditional handheld refractometers, Abbe refractometers, digital refractometers and inline process refractometers.

 Common Uses of Refractometry

• Refractometry is commonly used for quality control in the beverage industry, sugar industry, and distilleries, to check the percentage of sugar in juices and solutions, or alcohol in beer or wine and water purity
• In the food-processing sector, Refractometry is used to measure sugar percentage, acidity, and gelling agent concentration 
• Refractometry is used in medical testing for determination of total protein in serum or  plasma
• In the chemical industry, various industrial chemical solutions can be monitored for dissolved substances using Refractometry. Pulp and paper manufacturing processes utilize industrial refractometers for green liquor and black liquor monitoring.
• In the pharmaceutical industry for analysis of drugs
• Refractometry is also used for purity investigation of diamonds and forensic analysis of glass

Advantages of Refractometry

• Quick and simple technique
• Provides a quantitative estimate
• Portable equipment can be used in field conditions

Limitations of Refractometry

• Sample needs to be transparent to incident wavelength
• Calibration Standards are needed
• Wavelength and temperature used for calibration and measurement may not be identical, especially when using published calibration data

Industrial Applications of Refractometry

• Food and beverages
• Environmental testing
• Chemical manufacturing
• Pulp and paper manufacturing
• Medical testing
• Pharmaceutical testing
• Forensic analysis of glass
• Purity testing of diamonds