1 Introduction
1.4
Function of the OSMOMAT auto
The sample solution is cooled with a peltier cooling system while its temperature is electronically
monitored. Once the sample solution has reached a specific temperature below the freezing point,
crystallization is automatically initiated. The OSMOMAT auto initiates crystallization by injecting the
sample with a stainless steel needle that is cooled by a secondary upper cooling system and has
small ice crystals formed by moisture in the air on its tip. When crystallization begins, ice forms
spontaneously. The heat that was removed during undercooling is released again, the temperature
rises spontaneously, and the temperature of the sample rises to the freezing point.
If the sample consists of water (solvent), equilibrium is achieved as long as the sample contains water
and ice. The temperature remains constant because further heat removal does not result in a lowering
of the temperature but the formation of ice. The time of temperature equilibrium is known as
plateau
time
. Only after complete crystallization does the temperature fall again.
If the sample consists of a solution, the pure water in the solution crystallizes spontaneously and the
substances move to the rest of the solution. This means that at the time the freezing point temperature
is measured, the concentration is higher than in the original solution. A plateau occurs here as well,
but it is inclined. The osmolality reading is taken at the resulting reversal point (see Fig. 1). The
temperature is measured with a resolution of 1.858 x 10E-3°C.
Fig. 1 Freezing Point Depression of Solvent
Introduction
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