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What is Osmometry?

Osmometry is an advanced analytical method for determining the osmotic concentration of solutions. The osmotic – or solute – concentration of a colloidal system is expressed in osmoles (Osm) per unit of volume (Osm/L) or weight (Osm/kg). In clinical and formulation contexts, osmolarity/osmolality refers to solutes as small as ions which require exceptional sensitivity down to the milliosmole (mOsm) range. At such scales, the minute physiological conditions of solutions matter greatly.  

In this article, KNAUER explores some of the basic principles of osmometry in more detail.

Osmometry: Introducing tonicity

By measuring the total solute concentration of samples, osmometers can define the extent to which a solution can move water through a semipermeable membrane via osmosis. This is called tonicity. There are three underlying types of tonicity in osmometry; each expressed as relative to a solution separated by a semipermeable membrane:  


Different types of osmometry

Various osmometer configurations have been developed to measure the concentration of solutes in various sample types using a choice of colligative properties. For instance, vapor-phase osmometry exploits the relationship between boiling point and vapor pressure to measure solute concentration.  

Membrane osmometry is more conventional in that it employs a physical semipermeable membrane separating two distinct chambers containing solvents. As an osmol refers to the amount of substance in solutions that exert a specific osmotic pressure (~22.4 atmospheres), the measuring value in membrane osmometry is the low-pressure of each chamber. Determining relative pressure offers quantitative insights into osmotic concentration which can, in turn, assist with characterizing tonicity.

The most advanced method of osmometry used today is known as freezing point osmometry. A freezing point osmometer monitors how a sample’s freezing point changes according to its solute concentration. With a precisely linear correlation between a sample’s freezing point and its osmolality, freezing point osmometry offers one of the most accurate assessments of osmotic concentration.

If you would like more information about KNAUER’s freezing point osmometers, simply contact a sales representative today.  

Freezing point osmometry by KNAUER

KNAUER is one of the world’s leading specialists in reliable and user-friendly freezing point osmometry for a range of markets. Our K-7400S is a flexible solution for measuring the osmotic concentration of a wide range of sample types. If you would like more information, contact us today.

Applications of freezing point osmometry

The ease-of-usability associated with freezing point osmometry has opened a range of avenues of application beyond healthcare and pharmaceutical markets. At KNAUER, we provide reliable osmometers for food analysis, pharmaceuticals, and various research-based applications.

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