Membrane osmometry
The membrane osmometry is a method of osmometry for the determination of the molar masses about the determination of the osmotic pressure of solutions.
The membrane osmometer consists of an osmotic cell which is divided into two halves by a semipermeable membrane and housed in a thermostat in order to be able to determine molar masses of substances whose solubility lies in a higher temperature range. For the membrane u. a. regenerated cellulose or cellulose triacetate is used.
In the lower half of the measuring cell, which is hermetically sealed to the outside and which is filled with the pure solvent (water or an organic solvent), a sensitive pressure sensor is installed that can measure even the smallest pressure differences. Alternatively, the lower half of the measuring cell is connected to a sensitive pressure measuring system that is located outside. The upper half of the measuring cell is arranged above the semipermeable membrane. A filling and an outlet device are used to rinse and fill the measuring cell with the respective solution. The osmosis between the solvent and the solution creates a negative pressure in the lower half of the cell with the pure solvent, which is measured and represents the osmotic pressure . The osmotic pressure is not read directly, but is calculated using the cell constant, which must be determined by calibrating the measuring cell before the measurement.
Because of the possibility of measuring even a very small pressure difference, the method is particularly suitable for determining substances with large molar masses (up to 10 6 g / mol), e.g. B. of polymers.
See also
swell
- Römpp: Basic Lexicon of Chemistry. Georg Thieme, Stuttgart 1999, ISBN 3-13-115711-9
- Chemistry Uni Potsdam (PDF; 120 kB)