Short Note No. 111/2013
Boiling point determination according to Siwoloboff and Ph.
Eur. – a comparison
A study performed by TECHPharm GmbH using the M-565 confirmed that boiling point determination according
Siwoloboff and according to Ph. Eur. 2.2.12 lead to the same boiling point.
1. Introduction
obtained with Melting Point M-565 device confirmed
those obtained with the distillation apparatus.
An inherent characteristic of a pure liquid substance is
its boiling point. By definition, the boiling point refers to
the temperature at which the vapor pressure equals
the ambient pressure. For comparability reasons, the
boiling temperature is usually corrected to the
temperature at which the vapor pressure of the liquid
is equal to 101.3 kPa. [1]
In addition to the ambient pressure, the boiling point
depends on the molecular weight, the molecular
structure, intermolecular forces and impurities of the
liquid analyzed.
Here, two established boiling point determination
methods are compared.
The first method, already described by Siwoloboff in
1886, is preferentially applied to small amounts of
liquid. [2] For the Siwoloboff method a boiling point
capillary is immersed in a drop of liquid placed in a
boiling point tube. Upon heating, bubbles rise in the
liquid and ultimately form a constant rising bubblechain at the boiling point (Figure 1). At the boiling
temperature the bubbles are released from the boiling
point capillary at a frequency of 0.6 Hz.
Figure 2. Boiling and melting point device M-565.
Sample
Boiling point
specification
[°C]
Ethanol
DMF
Glycerine
about 78*
151-154
192-196
Boiling point
acc. to Ph.
Eur. 2.2.12
[°C]
78
152
194
Boiling point
acc. to
Siwoloboff
[°C]
78
152
193
Table 1: Comparison of specified boiling point and boiling
points according to Ph. Eur. 2.2.12 and Siwoloboff. [3]
*acc. to Ph. Eur.
4. Conclusion
Boiling point determinations according to Siwoloboff
confirmed the results obtained by measuring the
boiling point according Ph. Eur. 2.2.12 and the
specified boiling point temperature.
Compared to the Ph. Eur. method the boiling point
determinations according to Siwoloboff require only
small sample volumes of 250 µl. Further important
advantages of the Siwoloboff method are due to the
use of a commercial device, the M-565 which
i)
accelerates
the
boiling
point
determination compared to the Ph. Eur.
method
ii)
automates the process due to gradient
programming
The second method is for larger sample quantities, i.e.
20 ml or more, and described in detail in Ph. Eur.
2.2.12. [1]
iii)
improves reproducibility
iv)
allows post-experimental analysis due to
recording function
2. Experimental
v)
enables print-out of results for GMP
compliance
vi)
relies on a temperature calibration
traceable to primary standards
Figure 1: Boiling point determination of water according to
Siwoloboff. For water a constant rising bubble-chain is
observed at 100 °C.
All experiments were conducted by TECHPharm
GmbH Germany. For the Siwoloboff boiling point
determination the BUCHI M-565, was employed.
Common laboratory distillation glassware was used for
the Ph. Eur. method. For details regarding the
apparatus we refer to Ph. Eur. 2.2.12 method.
The boiling point of ethanol, N,N-dimethylformamide
(DMF) and glycerine was determined. For each
substance either 250 µl for the Siwoloboff method and
20 ml for the for the Ph. Eur. procedure were needed.
3. Results and discussion
Obtained boiling points are shown in Table 1.
Comparing the boiling point detected using both, the
Melting Point M-565 and a distillation apparatus
according Ph. Eur. 2.2.12, revealed that the results
5. Acknowledgement
We thank TECHPharm GmbH Germany for sharing
their results and for the kind support by Dr. Ulrike
Steiner.
6. References
[1] Ph. Eur. 2.2.12, European Pharmacopeia 7.0.
[2] A. Siwoloboff, Berichte der deutschen chemischen
Gesellschaft, Vol. 19, issue 1, p. 795–796, 1886.
[3] http://www.techpharm.de