Osmolality and Osmolarity

Osmolality and osmolarity are measured with an osmometer and they tell how much a liquid contains dissolved substances. The analysis can be done for small sample sizes, without loss of quality and accuracy. The test reveals the amount of osmotically active substances in the sample. Osmometry is a typical quality control measurement in many industries, such as pharmaceuticals, supplements and the food industry.

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There are two common units to measure and report osmometry of a solvent, osmolarity and osmolality (first one with an “r” and latter with an “l”).

Osmolality (with an “l”) is the number of osmoles (Osm) of solute per kilogram of solvent (osmol/kg or Osm/kg), whereas osmolarity (with an “r”) is the the number of solute particles per liter of solvent (osmol/L or Osm/L)Osmolarity is also known as osmotic concentration.

A typical technique to measure osmolality is the freezing-point depression test. Freezing point depression osmometer measures the freezing point of the solution to determine its concentration. The freezing point of a solvent lowers when another compound is added. This means that a liquid with dissolved compounds has a lower freezing point than the pure solvent. Higher the osmolality, lower the freezing point. Freezing point is an accurate tool because it correlates linearly with the osmolality.

To obtain reliable results the sample must have low viscosity. The accuracy of the test may be impaired if the solution is colloidal or has a high concentration of dissolved compounds.

Along with the medicine and pharmaceuticals manufacturing industry the measurements are  also used in food and beverage quality control.

Suitable sample matrices

  • Aqueous samples
  • Liquid pharmaceutical solutions
  • Liquid food supplement solutions
  • Sports drinks
  • Beverages
  • Other liquid goods

Ideal uses of Osmolality and Osmolarity analysis

  • Analysis gives exact concentration of osmotically active substances in a solution.
  • Tonicity is a key measurement for finding out the drug absorption qualities.
  • The method is used to measure tonicity of sports drinks.
  • Quality control of liquid pharmaceuticals and supplements.

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Frequently asked questions

What is the osmolality test commonly used for?

Osmolality and osmolarity are often used in the pharmaceutical industry as a quality control measurement before the liquid drugs are released to market.

Osmolality analysis gives information about isotonicity, consistency, formulation and stability. 

Analysis gives insight into process development, brewage and food product quality control.

What are the limitations of the osmolality test?

Sample should have low viscosity.

Accuracy of the test decreases if the sample has very high molarity. Samples with high concentrations of dissolved compounds can be diluted before the analysis to lower the concentration.

What kind of samples can be analyzed with the osmolality test?

Liquid samples with not too high viscosity and not too high concentration.

What is the difference between osmolality and osmolarity?

Osmolalitys definition is Osmoles of solute per kilogram of solvent  (osmol/kg or Osm/kg)

Osmolaritys definition is Osmoles of solute per liter of solution (osmol/L or Osm/L)

What is Measurlabs?

Measurlabs offers a variety of laboratory analyses for product developers and quality managers. We perform some of the analyses in our own lab, but mostly we outsource them to carefully selected partner laboratories. This way we can send each sample to the lab that is best suited for the purpose, and offer high-quality analyses with more than a thousand different methods to our clients.

How does the service work?

When you contact us through our contact form or by email, one of our specialists will take ownership of your case and answer your query. You get an offer with all the necessary details about the analysis, and can send your samples to the indicated address. We will then take care of sending your samples to the correct laboratories and write a clear report on the results for you.

How do I send my samples?

Samples are usually delivered to our laboratory via courier. Contact us for further details before sending samples.

Measur provides fast and reliable osmolality and osmolarity tests for your needs. The test gives the exact molarity of your liquid sample. Accredited laboratory for osmolality testing.