Freezing Point Osmometer

KNAUER is one of the pioneers in the field of osmometry and known for its reliable and user friendly instruments for many decades. Our newest freezing point osmometer K-7400S allows the easy and fast determination of the osmolality of various aqueous solutions. Also, the freezing point depression of the samples can be read.

The proven technology of freezing point determination in combination with the robust and intelligent design of the device allows fast and reproducible measurements. The instrument is equipped with a peltier cooler and an integrated microprocessor controlling the automated measurement.

Learn more about the theory of osmomality and osmometry below!

more about osmolality 

  • Theory
  • Principle
  • Process
  • Theory of osmolality  

    Osmolality is a general measure of the particle concentration in a solute. It´s not depending on the nature of molecules but just their number. Therefore, a two molar solution of a non-dissociating molecule (A) has the same osmolality as a one molar solution of a fully dissociating salt composed of two ions (B). The osmolality of a solution is the same, even when molecules vary in shape (C) as well as in size (D). Therefore, all solutions containing the same number of osmotically active particles — regardless of their chemical properties — exhibit the same osmolality.

  • Freezing point osmometry

    The measurement principle of the K-7400S Semi-Micro Osmometer is based on the colligative property of freezing point depression. If a solute is added to a liquid this results in a decreased freezing point of the solution. The depression is 1.858 K per 1 mole of ideally solved compound in one liter of water. This effect depends only on the number of particles in the liquid and not on the physical or chemical properties of the solutes. Due to this linear correlation, the osmolality of a sample can be determined by precisely measuring its freezing point.

  • Measuring process

    At the beginning of a measurement the sample is cooled by a microprocessor-controlled peltier element. During this process, the solution is supercooled below 0 °C while still being liquid. At a certain temperature the freezing process is initiated by a rotation of the stirring wire. The formation of ice crystals causes the release of thermal energy, thus rising the temperature of the sample. After a short period of time an equilibrium is reached where melting and thawing of ice crystals are balanced and the sample’s temperature stays constant. This plateau marks the real freezing point of the sample. During the whole process the temperature of the solution is measured by a high-precision thermistor. Thanks to a resolution of 1/1000 K the freezing point temperature is exactly determined and even small differences in osmolality of two samples can be measured.

Quality control of pharmaceutical solutions by determination of osmolality

The osmolality of solutions used in the clinical and pharmaceutical field is an important issue that requires regular monitoring. Especially infusion solutions but also solutions for external use like eye drops and rinsing solutions must be isotonic to ensure the physical well-being of humans. In this study, the osmolality of commercially available pharmaceutical solutions were determined using the KNAUER K-7400S Semi-Micro Osmometer.

Determination of osmolality of isotonic and non-isotonic beverages

In the last years isotonic beverages have become more and more popular. Almost every drink is available in an isotonic version. But what does isotonic mean and what are its benefits? How can be checked that beverages are really isotonic? And have you ever heard of osmolality?

Osmometer Reviews

In many laboratories, the accurate concentration of solved molecules in a liquid is essential for daily work routine. The KNAUER K-7400S Semi-Micro Osmometer is ideally suited for this task, since most solutes in a liquid can be measured. The determination of total particle concentration or osmolality becomes fast and simple. KNAUER is one of the pioneers in the field of osmometry and is known for its reliable and user-friendly instruments for many decades.

Get your osmometer care-free package

Order the KNAUER osmometer care-free package today and start your osmolality measurements "tomorrow".

When ordering the Freezing Point Osmometer (order no. A0006C) you will receive everything you need to start measuring the osmolalities of your aqueous solutions right away. With our care-free package you will be able to install your osmometer and start the measurements fast and easily. Detailed instructions as well as online video tutorials will support you with every question you might have.

That's what the users say

  • "When I got introduced to the K-7400S Freezing Point Osmometer I was very surprised how easy it was to use. The installation, as well as the setting up the operation are very fast and the user can do everything without further support from a technician."

    Dr. Hanna-Maija Hiltunen, Product Manager Osmometers

    See comparison

Osmolalities of the world

We analysed water around the world to create the first osmolality world map

Would you like to take part in creating the first osmo- world map? Send us your sample!

Regardless if there is the sea, a lake, a pond or a river right on your doorstep – just send us a small sample of it (1 ml in a sample tube). We will analyse it for you and add it to our map. Please take care to not use a vessel made of PE to store your sample, since this can lead to impossibility of analysis.
Send your sample to:

Att: Hanna Hiltunen
Hegauer Weg 38
14163 Berlin


EuroOsmo 7400 control software

The K-7400S Semi-Micro Osmometer is a standalone device. Therefore, all functions of the instruments are accessible via the keypad. For additional storage and data management functions users can work with the EuroOsmo 7400 software. It offers a user-friendly interface to control the K-7400S Semi-Micro Osmometer via PC.

Measurement parameters can easily be changed and sent to the instrument via the software. For each sample a temperature curve is displayed to visualize the measurement process. Samples can be named individually and the measurement results can be saved for archiving. The data can also be exported in different file formats (e.g. *.xls, ASCII or Tab delimited text files). Thus, also the import to laboratory information management systems (LIMS) is possible. Supporting the use of a barcode scanner, sample identification can be transferred automatically reducing the risk of wrong sample assignment.

We have prepared a series of video tutorials on EuroOsmo 7400. Check them out here.

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