Osmomat 090 Membrane osmometer

The Osmomat 090 enables the measurement of the average molecular weight (Mn) of polymers that are soluble in aqueous or organic solvents within the range of 10,000 to 2,000,000 g/Mol.

The measurement is highly dependent on the membrane that is used. Gonotec offers membranes with different "cutoffs" that are made of different materials, so that a suitable configuration can be offered for most applications.

This cell unit must be operated by a Gonotec Control Unit SA or Control Unit B.


  • high-performance measuring cell
  • short response times
  • small sample volumes
  • highest measuring resolution of 0.1 mm liquid column per digit
  • avoids "balloon effects"
  • membrane diameter of 40mm

Key data

Smallest detectable pressure
0.1 mm solvent column
Molecular weight range
5,000 to 2,000,000 Dalton, lower range depending on the semi-permeable membrane
Measurement cell volume
approximately 0.5 mL
Membrane diameter
40 mm
various organic solvents, water and aqueous electrolyte solvents
Sample vol. of polymer sol.
minimum 3 solutions of 2 mL each (with stepped concentration in the range of 1 to 5%)

Measurement: Membrane osmometer

Membrane osmometer

A membrane osmometer consists of an osmotic cell which is located in a cell thermostat. The osmotic cell is divided into two sections by a semipermeable membrane.

In the lower section, a hermetically sealed cell which is filled with pure solvent, a precision pressure measuring system is installed. The upper section, which is positioned above the semipermeable membrane, is designed as a meander-shaped channel system with a large surface. A funnel tube and a discharge valve enable rinsing and filling of the cell with solvent or polymer solution.

Due to the osmotic pressure difference between solvent and solution, a vacuum, which is related to the concentration of the osmotic actively solute particles, is generated in the lower cell half.