Chapter 1:
OsmoPRO MAX Overview
OsmoPRO MAX Automated Osmometer User Guide
15
Instrumentation
Advanced Instruments osmometers measure the freezing
point of an aqueous solution to determine solute
concentration. Advanced Instruments osmometers use
high precision thermistors to sense the sample
temperature and control the degree of supercooling. They
can routinely determine differences of ± 1 mOsm/kg
H
2
O
.
Freezing-Point Thermodynamics
The quickest and most precise way to measure the
freezing point of a solution is to supercool it to several
degrees below its freezing point and then induce
freezing. The solution is in a quasi-stable condition in this
state. At this point a separate thermal element is used to
induce crystallization. The sudden liberation of the heat
of fusion causes the sample temperature to rise rapidly
toward a
plateau
temperature. The plateau temperature
is the freezing point of the solution.
The following typical freezing curve illustrates the temperature of a sample as it progresses through the measurement
cycle and shows the action of the instrument at each stage of the cycle.
