Refractometers visit report
Extracts from this document...
Introduction
Abigail Durling
Visit Report
For my visit report I visited Aimia Foods, a company who specialise in producing soft drinks. I have chosen two pieces of equipment used by the company in the Quality Assurance / Research & Development Departments. Both are used to measure liquids. One of them is a polarimeter used to detect faults in essential oils and other solutions, the other is a refractometer, used to calculate the concentration of dissolved substances in water.
The polarimeter is mainly used to check the quality and integrity of expensive essential oils such as lemon oil, used in the flavouring of soft drinks. It would be used on in-coming raw materials.
The refractometer is much more widely used in the day-to-day measuring of syrup brix, a key quality attribute of all soft drinks.
Polarimeter
Polarization physics restrict vibration of light: to cause light to vibrate within particular planes, or vibrate in this way [Oxford dictionary of English]
A polarimeter is a piece of equipment used in the food industry to measure the optical rotation of solutions.
Middle
Water | Concentrated |
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www.nationalmicroscope.com/faq.html
Refractometers, devised by Dr. Ernst Abbe, are instruments which can be used to work out the concentration of water based solutions, by measuring the angle of refraction. In the food industry, sugar or salt solutions are measured this way. The refractometer utilises one of two systems, the older scale read transparent system and the newer digital reflection system. Using Snell’s Law of refraction, the refractive index of a substance can be obtained using the speed of light in a vacuum (v1) and also the speed of light in the substance (
. The speed of light in two mediums and the angles of incidence and refraction are both directly proportional to the refractive index. Hence we can work out the refractive index of a substance using the angle of incidence (i) and the angle of reflection (r).
Refractive index = 
= 
The Transparent System
A sample solution is placed on a prism of much greater refractive index than the sample.
Conclusion
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The refractometers internal software can then convert this into a usable scale: oBrix for sugars solutions, oBaume for saline solutions. This shows the concentration percentage of the soluble solids content of the water based solution.
e.g. Brix Scale (sucrose)
oBrix | RI |
0.0 | 1.3330 |
5.0 | 1.3403 |
10.0 | 1.3479 |
15.0 | 1.3557 |
20.0 | 1.3639 |
25.0 | 1.3723 |
30.0 | 1.3811 |
35.0 | 1.3902 |
40.0 | 1.3997 |
45.0 | 1.4096 |
50.0 | 1.4200 |
55.0 | 1.4307 |
60.0 | 1.4418 |
65.0 | 1.4532 |
70.0 | 1.4651 |
75.0 | 1.4774 |
80.0 | 1.4901 |
85.0 | 1.5003 |
http://www.coleparmer.com/techinfo/techinfo.asp?htmlfile=BrixScale.htm&ID=35
Refractometers are quick and reliable instruments, but do have limitations of accuracy depending on the temperature of the solution being measured. Temperature affects the solution density and thus the speed of the light passing through it. Correction tables are usually provided to amend the indicated brix/baume reading on older manual refractometers. Correction is automatic on more modern digital machines. The older transparent systems are limited in range and accuracy, the prisms operating in tight brix bands. One newer digital refractometer can replace several hand held prism refractometers.
This student written piece of work is one of many that can be found in our AS and A Level Modern Physics section.
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