K-7400S Semi-Micro Osmometer Article No.: A0006AC 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. In addition, the freezing point depression of such samples can be measured. 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. The freezing point Osmometer is a standalone device that optionally can be equipped with a printer. Furthermore, the device can be controlled via the EuroOsmo 7400 software. The software automatically plots the temperature curve for each measurement and calibration and allows saving of the measured values. In addition, the data can optionally be exported into various file formats for archival storage. The K-7400S Semi-Micro Osmometer complies with the European Pharmacopoeia for osmolality (2.2.35, 01/2012).
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.
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.