- Vapor pressure osmometry
Vapor pressure osmometry is a technique to measure the number average
molecular weight of a polymer. It is based uponRaoult's law that governs change invapor pressure of a solution based on themole fraction of the solute.The vapor pressure osmometer is composed of two chambers: one for pure solvent and the other to contain solution, where the solute is the polymer whose molecular weight is unknown.
Thermistors in each chamber provide an electrical signal (the actual measurement) of differential heating to achieve a vapor equilibrium in each chamber.By measuring solutions of different concentrations of solute with a known molecular weight standard, a plot of concentration versus electrical differential can be prepared. Similarly, the unknown is then prepared and measured with the number average molecular weight derived from the standard plot.
Wikimedia Foundation. 2010.