Osmometry

The osmometry uses the osmotic pressure for the analytical determination of the concentration and / or molar mass of a solution (or the molecular weight distribution ).

In the osmometer , an analytical instrument, the osmotic pressure is measured by cooling the sample below the freezing point. This can then be changed by transforming the size equation

${\displaystyle \pi =-RT\cdot \sum _{i=1}^{N}\Delta c_{i}}$

to the desired value for the concentration or the molar mass . ${\displaystyle c}$ ${\displaystyle M}$

Determination of the molar mass

The following relationships are to be used to determine the molar mass:

Osmotic pressure : ${\displaystyle \Pi =c\cdot R\cdot T}$

Amount of substance concentration : ${\displaystyle c={n \over V}}$

Amount of substance : ${\displaystyle n={m \over M}}$

Inserted and resolved according to the molar mass, the following applies: ${\displaystyle M}$

${\displaystyle M={{m\cdot R\cdot T} \over \Pi \cdot V}}$

${\displaystyle m}$: Mass of the solute

${\displaystyle R}$: Gas constant

${\displaystyle T}$: Temperature

${\displaystyle V}$: Volume of the solution

Procedure

Common methods of osmometry are:

• the membrane osmometry and
• the vapor pressure osmometry .

Individual evidence

1. ↑ Axel M. Gressner, Torsten Arndt: Lexicon of Medical Laboratory Diagnostics . 2nd, revised and expanded edition. Springer, Berlin, Heidelberg 2013, ISBN 978-3-642-12921-6 , pp. 1027 , doi : 10.1007 / 978-3-642-12921-6 .