BUCHI Melting Point M-565 - Manual (Page 36)

6 Operation
36 Melting Point M-565 Operation Manual, Version D
6 .2 .7 .3 Melting point thermodynamic
• In the settings, change the
melting result to Melting
point thermodynamic
and press
Save.
Experimental measurements
have shown that in most cas-
es a good approximation to
the factor for thermodynamic
correction of the BUCHI Melt-
ing Point M-565 is a value of
~1.5. Empirical calculation for
thermodynamic correction is
recommended when more ac-
curate results are required for
specific substances.
In order to obtain a thermodynamic melting point result within the accuracy of the unit, the following
steps are advised:
• Perform complete automatic pharmacopoeia melting point determinations on your sample at three
different temperature ramping rates: 0.2, 0.5, 1.0 °C/min.
• Plot the resulting melting points versus the square root of their corresponding temperature ramping
rate (mp pharmacopoeia vs. gradient )–a linear dependence should be observed.
• The slope is the thermodynamic correction factor. Enter this value in the setting 6.6 “Thermody-
namic correction.”
An example of this calculation procedure is shown below:
Gradient, r [°C/min] Melting Point [°C]
0.2 236.1
0.5 236.6
1.0 236.9
236.9
236.8
236.7
236.6
236.5
236.4
236.3
236.2
236.1
236.0
0 0.2 0.4 0.6 0.8 1 1.2
gradient
mp pharmacopoeia vs. gradient
y = 1.2684 x + 235.52
“Melting point temperature vs. gradient”
for a caffeine sample melted at 0.2, 0.5,
and 1.0 °C/min. The slope of the straight
line, factor for thermodynamic correction
= 1.3, is programmed into the setting of
instrument for this compound.
Fig. 6.2: “Melting point temperature vs. gradient ”