Knauer K-7400S - Important Operating Notes

Semi-Micro Osmometer K-7400S instructions, V3700
Operation 24
> ERROR <
NO FREEZE
If the crystallisation occurs before the start of the stirring wire, the mea-
surement will be stopped with the following error message:
> ERROR <
FREEZE
Device defect
If the sample tube is removed from the measuring head while the
sample or the calibration solution is frozen, the thermistor or the stirring
wire can be damaged.
When the message „next sample“ appears on the display, the sample
tube is safe to remove.
Note: The sample melting can be quickened by warming up with the
fin gers. When “next sample“ appears below the measurement value, the
sample is unfrozen, and it is save to remove the tube.
7.9 Important operating notes
1. The device is only suitable for aqueous solutions.
2. Only use sample tubes which were obtained from KNAUER or recom-
mended by KNAUER. Sample tubes should not be reused.
3. To ensure a fixed sample volume, always introduce the solutions with
a clean and dry pipette tip into the sample tube. Make sure that there
are no air bubbles in the liquid or drops on the tube wall above the
liquid. The sample solution should stand upright in the sample tube.
4. Handle the thermistor always very carefully. Do not use abrasive
materi als for cleaning. The thermistor should be cleaned occasionally
with a soft tensidic cleaning agent (dilution: 1:10 with water (HPLC
quality) about 40±5 ° C). After immersing, activate the stirring function
3 to 5 times for 5 seconds and rinse with water (HPLC quality). The
cleaning frequency depends on the used sample matrix. It is sucient
for pure saline solutions to rinse the thermistor with the following
sample solu tion. A dirty thermistor does not give accurate measure-
ment results.
5. Cleaning and drying the thermistor with alcohol or acetone is not rec-
ommended. High-frequency sources may compromise measurement
values. Remaining solvent vapours could cause false results.
6. Solutions containing proteins, such as sera, can only be measured
once. Freezing causes denaturation of the protein. A repetition of the
measurement with the same sample would result in increased values.
7. Please note the dierence between ideal and real osmolality. Only
real osmolality can be measured. It is not possible to prepare other
calibra tion solutions by dilution of a calibration solution since the
activity coe cient of the solution changes with dilution.