Refractometer Selection Guide
There are a number of things to consider when choosing the refractometer that is best for your requirements. These include cost, accuracy, temperature control, type and amount of sample, working environment, etc.
If you want for a low cost hand refractometer, look at our range of Visual Hand Held Refractometers, or consider the more expensive, but affordable, fully automatic Digital Hand Held range.
If you are looking for a more accurate bench refractometer for the laboratory or factory floor, we have a range of options to suit most applications in the food, pharmaceutical, oil, chemical and other industries as well as specialized models for measuring gases and vapours, contact lenses or the water content of the cornea during eye surgery.
There are many applications for refractometers in the sugar industry and if you want a system combining refractometer and polarimeter measurements to determine sugar content, apparent sugar purity or Dextran contamination, please look at the web page of our associated company Optical Activity Ltd.. For the sugar industry, Index Instruments also manufacture a colorimeter specially designed to make I.C.U.M.S.A. colour measurements.
TEMPERATURE is nearly always important in refractometry. All our automatic refractometers, for example the general purpose GPR 12-70 range, include pre-programmed temperature corrected Brix scales (the correction is made to I.C.U.M.S.A. recommendations) or can be programmed by the user to correct a refractive index (RI) reading if the temperature coefficient is known. For the most accurate readings, temperature control is usually required; this can be done by flowing fluid from a thermo-circulator (GPR 12-70 range), or by built-in electronic temperature control available on our PTR refractometers and on our TCR range. The GPR can control the sample temperature up to 70°C using flowing fluid. The TCR and PTR can operate up to 40°C or 50°C respectively.
For HIGH TEMPERATURE applications the GPR 12-70E model provides electronic temperature control up to 100°C.
RANGE and ACCURACY
The majority of bench refractometers for routine quality control are critical angle type refractometers – the familiar “Abbe” refractometer is a critical angle refractometer. These instruments are ideal for measuring Refractive Index (RI) or Brix over a wide range of values of commonly used liquids from dilute saline solution or soft drinks to oils or jams and jellies. The best critical angle refractometers read to the 5th decimal place of RI or the 2nd decimal place of Brix. Our widest range instruments are the PTR refractometers and GPR models, both ranges available in a choice of accuracies. Our TCR is high accuracy but a shorter range, limited to 0 to 95%Brix (i.e. RI 1.33 to 1.53). Our most accurate critical angle refractometer is the TMR 33-37 with a range of 0 to 25% Brix. Even higher accuracy is offered by the GR1 gas laser refractometer which measures the RI of gases and vapours, but not liquids, by an interferometric method.