Principles of Refractometry - Bellingham + Stanley - #2

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digital automatic refractometers use alight sensitive integratedcircuit (self-scanned array)to detect the exact position of the borderline.Bellingham+Stanley instruments also incorporatespecial software for interpreting ‘fuzzy’ borderlinesthat many products tend to produce. In this way,there is no subjective human judgement needed intaking a reading- a major advantage of an automatic instrument.When the composition of a substance changes, so does its RI. Thus a measure of RI canyield information about the composition of a substance. For example, when a substance isdissolved in a liquid the RI increases. Thus a measure of the RI of a sugar solution in watercan be used to determine the solution concentration .There are numerous uses and therefore refractometers are calibrated with one or more scales to suitthe particular application(s). For optical instruments a scale is visible via theinstrument eyepiece and readings are taken where the borderline intersects the scale. Withelectronic instruments, different scales can be programmed and the result is displayed indigital form.Apart from the fundamental Refractive Index scale, the Brix scale is the most widely usedscale on a refractometer. Brix, or sugar %, is an internationally recognised scale, whichrelates the concentration of sucrose in water at 20 C to the RI of the solution (wt/wt). Mostfood products are more complex than a sucrose solution; many other soluble ingredients maycontribute to the overall RI. However, the Brix scale is still used as the standard. For non-sucrose based products the term ‘apparent Brix’ is strictly more correct.More generally, refractometers are used to measure a RI of pure substances (liquid) as aunique characteristic, or used to measure the concentration of one substance dissolved inanother. Refractometry is therefore an ideal technique for Quality Control in manyindustries. The most common uses of refractometers are in the food and drink industries where the dissolved solids content of liquid food products is measured as a ‘Brix value’. Types of refractometers There are three main types of refractometer: portable hand-held instruments used for ‘on-the-spot’ measurements, high accuracy bench instruments for use in laboratories and process or‘in-line’ refractometers for monitoring and control in manufacturing processes.Bench type instruments can be further classified into two types: Abbe Refractometers These are optical-mechanical instruments and theyderive their name from the 19th Century physicist, ErnstAbbe. Automatic Digital Refractometers These are solid state electronic instrumentsincorporating flexible software and designed primarilyfor use in quality control applications.High accuracy may be achieved with both Abbe and Digital Automatic refractometers. Thelatter are generallymore expensive instruments and tend to be favoured by quality control laboratories. Bellingham+Stanley offers a wide range of refractometers covering all thetypes described above. The RFM Automatic Digital Refractometers are used by manycompanies in a variety of industries in over seventy countries and are regarded as leaders inmodern refractometry.
Bellingham + Stanley Ltd/Technical Bulletin No: R001 2 Modern