37
Melting point
B-540
6 Maintenance
Press the MENU key to leave the calibration menu.
After entering the values, the correction factors for the middle
and right hand columns are added together and entered in
the middle column. Thus, the values in the middle column
alter following each calibration and the right hand column is
then free for the next calibration.
6.3.4 Control measurement
The calibration is checked with verification substances. For
this we recommend the Set of verification substances, Büchi
Item No. 37667. It allows checks at the following tempera-
tures using four different substances:
The measurements are performed with the measurement
parameters recommended in section 6.3.1. The melting point
of each reference substance must be checked in at least
three measurements. The standard deviations should be less
than 0.3°C. The maximum permitted deviations of the mean
value from the theoretical melting point are as follows:
All measurement results of the calibration, the correction factors
entered and control measurement values should be recorded.
This allows the calibration to be checked and repeated at a
later date.
Substance
Melting Point*
Melting Point
Deviation*
4-Acetyl benzonitrile
ca. 60°C
±
0.2°C
m-Toluic acid
ca. 110°C
±
0.2°C
Sulfanilamide
ca. 165°C
±
0.2°C
Phenolphthalein
ca. 260°C
±
0.2°C
***** The exact values are specified on the packing as well as on the certificate from the manufacturer of the substance (Fluka AG).
Substance
Melting Point
Measuring
Total
Deviation
Accuracy
Deviation
4-Acetyl benzonitrile
±
0.2°C
±
0.3°C
>
±
0.5°C
m-Toluic acid
±
0.2°C
±
0.5°C
>
±
0.7°C
Sulfanilamide
±
0.2°C
±
0.5°C
>
±
0.7°C
Phenolphthalein
±
0.2°C
±
0.8°C
>
±
1.0°C
