Refractometry is the analytical method of measuring substances'

refractive index In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...

(one of their fundamental physical properties) in order to, for instance, assess their composition or purity. A

refractometer A refractometer is a laboratory or field device for the measurement of an Refractive index, index of refraction (refractometry). The index of refraction is calculated from the observed refraction angle using Snell's law. For mixtures, the index ...

is the instrument used to measure refractive index ("RI"). Although refractometers are best known for measuring liquids, they are also used to measure gases and solids, such as glass and gemstones. The RI of a substance is strongly influenced by temperature and the wavelength of light used to measure it; therefore, care must be taken to control or compensate for temperature differences and wavelength. RI measurements are usually reported at a reference temperature of 20 degrees Celsius, which is equal to 68 degrees Fahrenheit and is considered to be room temperature. A reference

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

of 589.3 nm (the

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

D line) is most often used. Though RI is a dimensionless quantity, it is typically reported as nD20 (or n), where the "n" represents refractive index, the "D" denotes the wavelength, and the 20 denotes the reference temperature. Therefore, the refractive index of water at 20 degrees Celsius, taken at the Sodium D Line, would be reported as 1.3330 nD20. Refractometers are frequently used by grape growers and

kiwifruit Kiwifruit (often shortened to kiwi), or Chinese gooseberry, is the edible berry (botany), berry of several species of woody vines in the genus ''Actinidia''. The most common cultivar group of kiwifruit (Actinidia chinensis var. deliciosa, ...

growers for Brix testing of

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

levels in their fruit. Refractometry is also used in the

gelatin Gelatin or gelatine () is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also be referred to as hydrolyzed collagen, coll ...

industry. To convert the RI of a

sol (reported in Brix) to a gelatin concentration, one need only multiply by eight-tenths (0.8). A sol with a 10.0 RI would therefore be 8% gelatin by weight. This is known to be a reliable conversion for gelatin sols as low as 1% up to over 50%.

Types of refractometers

There are four main types of fluid refractometers:

traditional handheld refractometer A traditional handheld refractometer is an analog instrument for measuring a liquid's refractive index. It works on the ''critical angle'' principle by which lenses and prisms project a shadow line onto a small glass reticle inside the instrume ...

digital handheld refractometer A digital handheld refractometer is an instrument for measuring the refractive index of materials. Principle of operation Most operate on the same general ''critical angle'' principle as a traditional handheld refractometer. The difference is t ...

s, Abbe refractometers, and inline process refractometers.

External links

Refractometry - Gemstone Buzz
methods for measuring refractive index. {{Authority control Measurement

Types of refractometers

Further reading

External links