9 Error Messages and Troubleshooting
9 Error Messages and Troubleshooting
The following explains the error messages reported by the unit along with their possible causes and
describes the proper use of measuring vessels.
9.1 Spontaneous
Crystallization
The freezing point of a solution is measured by first undercooling the solution, without any ice
formation, to a predefined temperature. Crystallization is then automatically initiated by injecting ice
crystals. A portion of the solution’s water content is crystallized out. The crystallization enthalpy
causes an immediate rise in temperature up to the freezing point of the remaining, somewhat more
highly concentrated solution. During the time in which both ice and solution are present, a freezing
plateau then forms. Since ice is constantly forming through the ongoing gradual cooling of the sample,
however, the concentration of the remaining solution increases steadily, leading to a steady increase
of the osmolality and thereby inclining the freezing plateau to a specific degree. The OSMOMAT auto
obtains a reading for the total osmolality by calculating the temperature difference between the
freezing point of the water and the reversal point detected while measuring the sample solution. The
OSMOMAT auto monitors temperature changes during the undercooling phase. If crystallization
begins prematurely, before the undercooling temperature of -7°C is reached, an error message is
displayed, the erroneous reading, which is too low in this case, is suppressed, and
“SPONT.CRYSTALLIZATION” is displayed under status.
9.2
Preventing False Readings Due to Spontaneous
Crystallization
The main cause of spontaneous crystallization is the presence of seed crystals, which prevent
undercooling to the proper temperature. Such seed crystals might be salt crystals, gas saturation or
any pre-existing ice crystals. Seed crystals of this type can be easily eliminated by briefly heating the
sample liquid close to its boiling point and subsequently cooling it. Seed crystals that cannot be
eliminated in this manner may be removable through filtration. Salt crystal formation may result when
cooling sample solutions containing certain salts on the solubility threshold due to low solubility or high
concentration. These salt crystals then act as seed crystals. In such cases, adequate dilution may help,
though precise results can no longer be expected
. (Also see chapter 9.3.1,
Excessive Osmolality
.)
Seed crystals can also adhere to the thermistor probe. Clean the thermistor probe thoroughly using
water and a soft paper towel to remove any seed crystals.
28 | Error Messages and Troubleshooting
