Refractometer / Brix Meter

A digital refractometer, also known as a brix meter, uses the total reflection method to measure the refractive index or related values of a liquid sample. This measurement is done digitally, reducing operator influence considerably. Accuracy of up to 0.00002 or 0.01% Brix can be reached, using a small sample volume (0.5 to 1 mL) and conducted in a short measuring time (a few seconds).

Digital refractometers use a light-emitting diode, a sapphire prism and a high-resolution optical sensor. A sample is put on the prism and the measurement is started. From a certain angle of incidence – the so-called critical angle – the ray of light no longer penetrates the sample, but is fully reflected from its surface and is detected by the optical sensor. The refractive index is calculated from this critical angle. In addition, benchtop digital refractometers / brix meters use a built-in Peltier thermostat to control the temperature of a sample.

Learn more about the definition of refractive index, applications, how to measure it, Snell's Law and much more.

The refractive index of a solution can be measured manually or digitally. Manual methods like a portable optical refractometer or an ABBE optical refractometer are widely used for the determination of refractive index and related values, e.g. BRIX°, alcohol %, Baumé, Plato, etc. Although these methods are easy to use and quite inexpensive, they require expertise in every step of the manual operation protocols, which often affects the accuracy and reliability of the results. Digital refractometers / brix meters are available as benchtop and handheld instruments. They measure liquid samples digitally, reducing operator influence considerably.

Compare digital refractometers with manual methods: View the different measuring techniques

For most bench-top refractometers the typical volume is around 0.5 mL for samples with high surface tension and 1mL for samples with low surface tension. As only a few drops are required, the temperatures of the sample and the measuring cell equalize fast and the analysis therefore takes only a short amount of time.

This depends on the temperature difference between the sample and the measuring cell, as well as the sample type and the required accuracy of the measurement. This measuring time is typically a few seconds.

Usually refractometers / brix meters are adjusted with water at a specific measuring temperature. This temperature is controlled with a Peltier element, which can cool down or heat up the measuring cell to a specific temperature (e.g. 20°C). Sometimes, Brix standards are used to adjust a refractometer for the measurement of sugar concentrations. These Brix standards are often produced onsite. Smart BRIX Standard Preparation can be done using a balance and a refractometer connected to LabX™ PC software, increasing accuracy and traceability, while eliminating transcription errors.

Learn more about how to test and adjust your digital refractometer.

Digital refractometers / brix meters were originally designed for measuring homogeneous liquids. In reality, many other samples can successfully be measured, such as pasty samples or even foils. These specific samples require some additional accessories, like a press or a foil stamp. Special care has to be taken for volatile samples (where a flow cell is recommended) or non-homogenous samples where the sample must be stirred/homogenized prior to the measurement. This can be done automatically with the in-beaker homogenizing of the InMotion™ autosampler.