The measurement of Refractive Index (RI) is an important parameter in a whole range of industries. There are several makes and models of refractometers available on the market, that vary in cost and complexity. The instruments fulfil to a varying degree, fitness for purpose requirements for various industries and various sample types. In some cases, RI measurement is heavily regulated, such as in the sugar industry and there have been a wide array of ASTM written standards produced for many applications. Irrespective of application, industry type, sample type, instrument used or target measurement uncertainty, high quality calibration standards are an imperative. These can also be used for quality control, method validation, analyst qualification or proefficiency testing. This paper details a brief explanation of the science of RI, how a typical refractometer works and presents some examples of instruments available in the marketplace. This is followed by narrative of the relevance of RI measurement and various ASTM standards that have been published depending on application.
The final section of the paper explains the reasons why high-quality liquid standards are necessary and then details specific RI standards available from Reagecon. It is important to point out, that there are other high quality manufacturers of such standards, but the Reagecon standards are presented here for example purposes, as these are most familiar to the author. In broad terms there are four main classifications of RI standards that include ICUMSA compliant and non-compliant sucrose standards expressed in Brix values, sucrose standards expressed as RI and solvent based standards expressed as RI.
It is hoped that this publication will provide the reader with a sound theoretical knowledge of RI measurement, and will provide a detailed knowledge of the metrology pertaining to RI and furnish the analyst with the knowledge and tools to procure and use RI or Brix Standards optimally.
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by John Barron