Refractometer Calibration For Industry Applications

Rudolph Research can assist with your refractometer calibration requirements providing the necessary calibration materials for your industry application.

Rudolph Research Analytical works with Cargille Laboratories to provide a range of refractometer calibration standards.

Refractometer Calibration standards are:

  • Supplied in 28ml bottles
  • Supplied with a calibration certificate traceable to the National Institute of Standards and Technology (NIST)
  • Shelf life of unopened bottle is 5years
  • Shelf life of opened bottle is 2.5 years
  • Fluids calibrate at temperatures between 20°C and 40°C are accurate to 0.0001 Refractive index
  • Fluids calibrate at temperatures above 40°C are accurate to 0.0005 Refractive index
  • Some fluids available with calculated Brix values
  • Some fluids available with calculated Urine Specific gravity numbers

Choosing a Refractometer Calibration Fluid

Rudolph Research Analytical offers two types of refractometer calibration fluids:

  • NIST traceable refractive index fluids
  • Brix standards made from sugar and water

This article is designed to serve as a guide as to which fluid will suit the application best.

Technical Considerations

Refractive Index Fluids Brix Fluids Advantages
Description of Fluids Refractive index fluids are made from chemical compounds such as methylene iodide, silicon oil and alpha bromonapthalene. These chemicals are chosen as they are non toxic though some of the fluids do have an unpleasant odor (alpha bromonapthalene = mothballs). Brix fluids are a mixture of sucrose and water. Brix fluids
They are so safe you could drink them. They are just sugar and water.
Traceability of Fluids Refractive index fluids are provided with a certificate showing traceability to a national standards body – NIST. Brix fluids are made using the method specified in ICUMSA and are provided with a non-traceable certificate of analysis. Refractive Index fluids
NIST traceability is the ultimate US standard.
Shelf Life Refractive index fluids have a rated life of 5 years unopened, 2.5 years opened. Care should be taken that they are not frozen, but otherwise they can be stored at room temperature. Brix fluids have a life of 30 days and must be kept refrigerated. Refractive Index fluids
Stored at room temperature for 2 years.
Clean Up After calibration with the refractive index fluids the refractometer must be cleaned with an organic solvent such as acetone. After calibration with the Brix fluids the refractometer can be cleaned with water. Brix fluids
No toxic solvents needed
Range Refractive index fluids are available over the full range from 1.30 – 1.70 Refractive Index and 0 – 95 Brix. Brix fluids are available over the range 0 – 67.5 Brix. Refractive Index fluids Wider range of calibration options
Temperature Dependency All fluids are temperature dependent. The refractive index fluids have a different temperature dependency than the temperature compensation setting on a refractometer and so can only be used on a temperature CONTROLLED refractometer. Brix fluids have the same dependency as a temperature compensated refractometer and so can be used on any instrument. Brix fluids
They can be used to calibrate hand refractometers as well as bench models.

Application Considerations

Refractive Index Fluids Brix Fluids Advantages
Type of refractometer Temperature controlled Refractometer is required. If the refractometer does not have a method of controlling temperature then the refractive index fluids will not work. This applies to all hand refractometers and also Abbe refractometers that do not have a water bath attached. It also applies to a few cheaper bench refractometers. For these refractometers the only choice is the Brix fluids. Brix fluids
Can be used for refractometer calibration with hand refractometers as well as bench models.
Ease of Use The refractive index fluids are supplied in a glass bottle with a glass dropper stick. The fluids last a long time (2.5 years minimum) but care must be taken to ensure the bottle is not contaminated. In general we would recommend that use of these fluids is restricted to users with some laboratory training. The Brix fluids are supplied in a dropper bottle and are more regularly replaced. This means they are much simpler to use for non-lab trained people. Brix fluids
Dropper bottles are easier to use than pouring down a glass stick
Temperature Range If the laboratory procedures specify measurement be controlled to a temperature other than 20°C then refractive index fluids calibrated at that temperature must be used. Brix is, by definition, calculated at 20°C. Refractive Index fluids
If the instrument is to be calibrated at a temperature other than 20ºC then refractive index fluids are the only choice.

Very General Shortcut – Use Like for Like

Use a fluid that is like the sample to be measured.

  • If the results are reported in Brix then use Brix standards
  • If the results are reported in Refractive Index then use Refractive Index standards.

Refractometer Calibration Standards