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DIFFERENTIAL SCANNING CALORIMETRY DSC AS A MEANS TO CHARACTERIZE Jojoba Oil
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DIFFERENTIAL SCANNING CALORIMETRY (DSC) AS A MEANS TO
CHARACTERIZE THE EXTERNAL PHASE IN WATER-IN-OIL- (W/O)
FORMULATIONS
Doris Koepper, Geoffrey Lee
Department of Pharmaceutics, University of Erlangen, Germany
Introduction The samples were kept in glass recipients with a
capacity of 15 ml and examined visually every day.
The stability of semisolid dosage forms can be
evaluated in the centrifuge or under accelerated • Polarisation Microscope (PM)
storage conditions. In case of instability, the The inner structure of the formulations was
formulation will phase separate. The liquid with a investigated with an Olympus Hamamatsu
lower density will form a liquid phase at the top of polarisation microscope to examine the existence
the system. and size of anisotropic structures or vesicles.
If the separated liquid is lipophilic in a water-in-oil-
(W/O) formulation, the instability is initiated by an • Rheology
unstable external phase. Changes of the melting The formulations were characterized with the
behaviour of dosage forms detected with Physica rheometer Rheolab MC 10 fitted with a
subambient differential scanning calorimetry have cone and plate of diameter of 50 mm.
been shown to correlate with the quality of the
dosage form, the quality of excipients used or • Production of the samples
structural changes in the dosage form [1]. The aim The samples were produced by melting. Three
of this study is to investigate the coherence of the mixtures were examined.
ingredients in the external phase of a water-in-oil- 1: Beeswax and Jojoba oil (17:10 by weight)
(W/O) formulation with the differential scanning 2: Beeswax, Jojoba oil, lecithin, etheric oil
calorimetry technique. (17:10:7:20 by weight)
Furthermore, the DSC results are compared with 3: Beeswax and Jojoba oil, lecithin, etheric oil,
stability studies, photographs under the polarisation water (17:10:7:20:46 by weight)
microscope and rheological measurements.
Results and discussion
Experimental methods
Differential Scanning Calorimetry (DSC)
• Differential Scanning Calorimetry (DSC) Comparing the heat flow of a mixture of beeswax
The samples were inserted into aluminium pans and and Jojoba oil with the heat flow of beeswax and
investigated with an alteration in temperature of 10 Jojoba oil alone shows that the ingredients are not
°C min-1 in a Mettler Toledo DSC 822e. The completely miscible (Figure 1). The peaks do not
procedure is composed of three successive steps combine into one another. Therefore a high thermal
with a heating, cooling and heating process from - stability cannot be reached.
30 °C to 80 °C, 80 °C to -30 °C and -30 °C to 80
°C. The changes in the DSC curves were evaluated J o jo b a o il
both with the positions of peak maxima and 60
M a x :-1 .6 4 ° C
In t:9 4 1 .5 4 m J
minima. The peak areas represent the phase-
transition enthalpies. 40
B eesw ax
Heat flow (mJ)
20 M a x :5 4 .0 3 ° C
In t: 6 7 6 .0 5 m J
• Stability studies
2.
0
For the centrifuge test, Eppendorf tips were used M in : 9 .3 9 ° C 1.
M in : 5 7 .8 4 ° C
In t:- 4 6 7 .0 1 m J
M in 5 9 .9 3 ° C
In t:-6 8 4 .1 7 m J
with a capacity of 1.5 ml. After centrifugation at
-2 0
In t:- 1 0 0 5 .2 7 m J
M in : 1 3 .7 7 ° C
3. In t:-9 3 8 .2 2 m J
4,000 rpm and 10,000 rpm at both 20 °C and 40 °C -4 0
-2 0 0 20 40 60 80
the liquid at the top was removed and the percental R e fe re n c e te m p e ra tu re (°C )
difference in weight calculated. Figure 1: DSC – Mixture 1
The accelerated storage conditions were 30 °C, 40
°C, and also -5 °C / 40 °C changing every 12 hours. When the mixture is additionally combined with
etheric oils, the extents of the DSC-peaks diminish
and the positions displace to lower temperatures
(Figure 2). The etheric oil distributes therefore
between the two phases and evokes a depression in
their melting points.
60
M a x :-1 6 .7 6 ° C
40
In t: 4 1 6 .4 9 m J
Heat flow (mJ)
20 M a x :4 3 .9 1 ° C
In t: 3 2 7 .8 8 m J 2.
0
3 .= 1 .
M in :4 8 .1 1 ° C 1.
-2 0
M in : - 1 .7 1 ° C
In t:5 0 0 .9 2 m J
In t:-3 5 5 .5 3 m J Figure 4: PM - Mixture 3
-4 0
-2 0 0 20 40 60 80
R e f e r e n c e te m p e r a tu r e ( ° C )
Rheology
Figure 2: DSC – Mixture 2 The controlled shear rate test characterizes the
speed of fluidity at a given shear stress. Mixtures 1
Stability studies and 2 are too solid to be examined. Only mixture 3
Tables 1 and 2 show clearly the good stability of is liquid enough to follow the given shear stress
mixture 1. With the addition of lecithin and etheric (Figure 5). The apparent yield point is located at
oil, or lecithin, etheric oil and water, the stability approximately 350 Pa. The use of rheological
diminishes greatly, however. measurements is therefore limited.
100
Storage 40 / -5 [°C] 40 [°C] 30 [°C]
conditions 80
Mixture 1 38 d >775 d >775 d
Mixture 2 0.5 d 0.5d 32 d
Shear rate (1/s)
60
Mixture 3 3d 3d 62 d
40
Table 1: Stability data under different storage
conditions
20
Centrifuge 20 [°C] 40 [°C]
4.000 10.000 4.000 10.000 0
0 100 200 300 400 500
[rpm] [rpm] [rpm] [rpm] Shear stress (Pa)
Mixture 1 stable stable stable stable
Mixture 2 stable stable 22.16 % 42.16 %
Figure 5: Rheology - Mixture 3
Mixture 3 stable 3.76 % 1.11 % 21.59 %
Table 2: Stability data from the centrifuge (stable
Conclusion
means homogeneous appearance after the
centrifugation)
The etheric oils have a negative influence on the
stability of the Jojoba oil/beeswax-mixtures. DSC is
Polarisation Microscope (PM) an helpful analytical method to examine the
The comparison of mixture 2 with mixture 3 under stability of new dosage forms.
the polarisation microscope shows coloured crystals
in the formulation without water (Figure 3) and a References
great number of vesicles and liposomes in the
formulation with water (Figure 4). [1] E. Schwarz and S. Pfeffer
Journal of Thermal Analysis 48 557-567 (1997)
Figure 3: PM - Mixture 2
