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Knauer's K-7400s 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. The newest freezing point Osmometer K-7400S allows for 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. Contact us for a quote –

Care-Free Osmometer K-7400s
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Made in Germany

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2-year warranty

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Great Value

Semi-Micro Osmometer K-7400
Semi-Micro Osmometer K-7400
  • Sample volume: 50 – 150 µl
  • Osmolality range: 0 – 2000 mOsmol/kg
  • Test time: ~ 2 min
  • Resolution: osmolality –  integer value without decimal part, e.g. 850 mOsmol
    temperature: value with three digits, e.g. -1.576 °C
  • Precision: SD ≤ 4 mOsmol/kg [0 — 400 mOsmol/kg]
    RSD ≤ 1 % [400 — 2000 mOsmol/kg]
  • Linearity: ± 1 % [0 -1500 mOsmol/kg]
    ± 1.5 % [0 – 2000 mOsmol/kg]
  • Calibration: Two-point calibration (0 mOsmol/kg and one freely selectable osmolality)
    optional: Three-point calibration (0 Osmol/kg and two free selectable osmolalities)
  • IQ/OQ certification available if required
  • meets the requirements of the European Pharmacopoeia for osmolality (2.2.35, 01/2012).

Delivered with:

  • Measuring head for plastic sample tubes (A0840-2)
  • Power cable
  • RS-232 connection cable
  • 500 Pack of sample tubes (A0272)
  • 400 mOsmol/kg calibration solution (A01241-1)
  • 850 mOsmol/kg calibration solution (A01250)
  • Pack of lint-free cleaning tissue (A02330)

For more information from the Knauer website go to

This video illustrates how easy the Knauer K-7400S osmometer is to use. The video covers the initial calibration of the system and the running of the first sample. (Video length 4:15)

Optional Products for the K-7400s Osmometer

EuroOsmo 7400 Software
EuroOsmo 7400 Software

EuroOsmo 7400 Software (Optional)

EuroOsmo 7400 is a user-friendly software developed for the freezing point Osmometers K-7400 and K-7400S. It allows control of the instruments and recording of the measured data. The software automatically plots the temperature curve for each measurement and calibration and allows saving of the measured values.

Plain paper printer for freezing point osmometer K-7400 and K-7400S (Optional)

For easy and quick documentation of your osmometry results, KNAUER offers an optional plain-paper printer. This is compatible with the current freezing point osmometer model K-7400S and the previous model K-7400. Included is a power supply, ribbon cartridge (black), and a roll of printer paper.

K-7400s Measuring Head
K-7400s Measuring Head

Spare Measuring Head, Part No. A0840-2

NaCl Calibrating Solutions
NaCl Calibrating Solutions

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.

Theory of 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.

Mechanism of Freezing Point Osmometry

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.

Freezing Point Osmometer Measuring Process

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