Instrument: UIC Vapor Pressure Osmometer


Physical and Mechanical Property Analysis


311 Chevron Science Center



The UIC 070 vapor pressure osmometer (VPO) is used to determine the number average molecular weight (Mn) of polymers or other non-volitile solutes in the molecular weight range of 100-25,000 Daltons (organic solvent, e.g. toluene) or 100-5,000 Daltons (aqueous). The VPO operates by measuring temperature changes with two matched thermistors in a solvent vapor filled chamber. An analyte solution and a pure solvent are injected onto the two thermistors, thereby altering the equilibrium in the chamber as the analyte sample pulls solvent vapor out of the chamber atmosphere. This results in a temperature change for the thermistor and a subsequent change in electrical resistance. This resistance change is compared to a calibration curve with known concentrations of the analyte to produce a concentration (osmolality) for the analyte.