A refractometer is a laboratory or field instrument used for measuring concentrations of aqueous solutions. It requires only a few drops of liquid and is used throughout the food, agricultural, chemical, and manufacturing industries.
Refractometers measure the degree to which 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 values, you can determine the concentrations of solutions.
Hand refractometers facilitate convenient and rapid measurement of concentration in a number of liquid and semi-solid samples. It works on critical angle principle in which lenses and prisms project a shadow line onto a small glass reticule inside the instrument, which is then viewed through a magnifying eyepiece.
Digital refractometers operate on the same critical angle principle as a handheld refractometer. The difference is that light from an LED is focused on the underside or a prism element. When a liquid sample is applied to the measuring surface of the prism, some of the light is transmitted through the solution and lost, while the remaining light is reflected onto an array of photodiodes creating a shadow line. Once the position of the shadow line has been automatically determined by the instrument, the internal software will correlate the position to refractive index and display a digital readout.