The refractometer is a laboratory device primarily used to measure the refractive index (RI) of samples. The refractive index is an indicator of the behavior of light on that sample. By knowing the refractive index, one can confirm the purity of a sample or measure its concentration. In cases of a sugar solution, the refractive index can be used to determine the sugar content. In scenarios like that in a production environment, a portable refractometer would be best suited because of its compact size and quick operation.


How does a digital refractometer work?

A digital refractometer is an automatic instrument which calculates the refractive index of the sample by determining the critical angle of total reflection. This working is based on Snell’s law.

The instrument setup consists of a light source, usually an LED bulb, that is focused onto a prism surface by means of a lens system. The prism surface is where the liquid sample is dropped onto. When light passes through the liquid sample, a part of the light is reflected onto a linear arrangement of photodiodes, thereby creating a shadow line. The refractive index is directly related to the position of the shadow line on the photodiodes. The internal software correlates the position of the shadow line to refractive index and displays the value on a LCD display.

KEM’s portable refractometer: RA-130

Kyoto Electronics Manufacturing Co., Ltd. manufacture their own line of portable instruments in Japan, with the portable refractometer as a prime product. The automatic digital refractometer, called the RA-130 is a light-weight instrument that does not require any technical expertise to operate. 

You can either allow the sample to drip onto the prism or the prism of the portable instrument can be dipped into the sample beaker to measure refractive index. It is a microprocessor-controlled instrument with a bright, clutter-free LCD display. It is equipped with an infrared port for transmitting data to a computer.

Calibrating a portable refractometer 

Calibrating any instrument is a must, especially if it is used for quality control. Calibrating your instrument helps you take note of any error that would have crept into your instrument as a result of wear and tear over the years.

Calibration is the process of comparing a known measurement, called the standard, with the measurement obtained using your instrument at hand. In the case of calibrating a portable refractometer, the standard in most cases is distilled water. On dropping a few drops of distilled water onto the prism, the LCD display in the instrument must show a reading of 0 Brix, which is equal to 1.3325 RI.

RA-130 feature highlights

Measurement range: RI - 1.3200 to 1.5000 & 0 to 85% Brix.

In-built data storage of 1100 measurement results.

Display measurement of refractive index, temperature compensated refractive index, percentage of Brix, HFCS42, HFCS55, and temperature in degree Celsius and degree Fahrenheit.

Auto-inactivity detection switches the instrument off when it hasn’t been used for a long duration. This increases the life time of the batteries. 

Option of automatic data saving and automatic data output.

Uses of portable refractometers

To measure the:

Concentration control on pharmaceutical and medical liquid samples.

Sucrose concentration in fruits juices.

Sugar content in beverages and liquid seasoning.


Pharmaceutical | Food Testing | Beverages | Chemicals | Flavors & Fragrances | Nanotechnology | Paints | Inks | Polymer | Fine chemicals

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