Technical Note
TN664
Boiling point measurement by DSC
Description
The boiling point of a pure compound is one of the essential information necessary before any industrial implementation.
Nevertheless, its determination needs very specific conditions to limit the influence of the atmosphere. Indeed, internal gas
convection, vapor pressure in the crucible or kinetic of vaporization are important factors that play an important role in the
measurement. To determine precisely the boiling point, those factors have to be optimized. The DSC technique can be
used for such a measurement
Onset : 27.4 (°C)
Octadecane
Peak Maximum : 312.5 (°C)
5
Heatflow (mW)
Onset : 121.6 (°C)
Peak Maximum : 249.7 (°C)
Benzoic Acid
0
50
100
150
Temperature (°C)
200
250
300
Experimental
Results
Samples:
The first endotherm corresponds to the melting of the
compound. The last endotherm relates to the transition of the
condensed phase into vapor. The onset corresponds to the
beginning of the phenomenon, and the top of the peak, to the
maximum of vaporization rate corresponding to the boiling
temperature.
Octadecane
Benzoic Acid
DSC 131 Evo experimental conditions:
Carrier Gas: Nitrogen 20ml/min, atmospheric
pressure
Sample mass: about 5 mg
Crucible: 100µl aluminum crucible, sealed with a
pierced lid
Experimental procedure:
The temperature is programmed as following:
• Octadecane: -20°C up to 350°C
• Benzoic Acid: RT up to 300°C
at 10°C/min in both cases
Instrument
DSC 131 Evo
-170°C up to 700°C
Octadecane
Benzoic acid
Melting temp. (°C)
27.5
121.6
Boiling temp. (°C)
312.5
249.7
Litterature for boiling point of pure materials:
- benzoic acid : 249.0°C and octadecane : 316.3°C
Conclusion
To optimize the measurement, the vaporization of the compound
has to be controlled. Hence, to prevent the complete vaporization
before boiling, few points have to be respected:
• The pin hole on the lid has to be as small as possible in order to
keep a constant pressure in the crucible, but limiting the vapor
diffusion through the hole.
• The gas flow must be very low to limit the convection.
• The temperature ramp has to be high enough to control
kinetically the vaporization
• The free volume in the crucible at the beginning of the
experiment should be large enough to contain the maximum of
sample once in vapor phase.
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