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Melting point
B-540
6 Maintenance
6.3.1 Melting point determination procedure for
the calibration
• The instrument should be calibrated at least once a year.
• The reference substances should be stored protected from
light in a desiccator over desiccant at room temperature
(15-25°C).
• The expiry date must be checked and the reference
replaced if necessary.
• The theoretical melting points of the reference substances
are known. An analysis certificate is provided and describes
how the theoretical melting points are determined.
• Three measurements are performed simultaneously for
each reference substance.
Recommendation:
Filling height:
4-5mm, as compact as possible by knocking
the filled capillaries on a hard surface, the
substances are ground in a mortar.
Gradient:
0.5°C/min
Setting point:
5°C below the expected melting point
Determine the clear melting point (sample melted completely
clear).
6.3.2 Evaluation of the melting point
determination
All measurements should be evaluated in accordance with
strict criteria and checked for their usability. For this we
recommend that at least the following parameters be checked
and the measurement repeated in the case of doubt.
• The melting procedure complies with the requirements.
• There should not be any bubbles which hinder visual eva-
luation of the melting procedure.
• The samples should not become discoloured.
• The samples melt within a narrow temperature range of
1°C.
The mean value is calculated and the standard deviation from
3 measurements is:
Vanilline
<0.3°C
Phenacetine
<0.5°C
Caffeine
<0.5°C