the system [23]. The characteristics of multiple emulsions
were investigated at the formulation stage as well as for
the followed 30 days at different conditions of storage i.e.
8°C, 25°C, 40°C and at 40°C with 75% relative humidity.
Furthermore, multiple emulsions were subjected to extensive
centrifugation at 5000 rpm for 20 min to accelerate
the phase separation of the system for the followed-up
period of 12 months to understand the stability.
No phase separation was observed in any of the
samples upon extensive centrifugation. Mean globule
size was in the range of 8.41±3 μm to 10.81±7 μm
(mean ± standard deviation). The sample that was kept at
8°C has shown smaller size of globules while an increase
in the globule size was observed with an increase in the
storage temperature. A maximum increase in the globule
size was observed at 40°C. However this increase in the
globule size with temperature does not seem to be a
significant as the coefficient of variation (CV) was only
varying in a narrow range at all the studied storage
temperatures. A larger CV indicates an unacceptable
limit of shrinkage or coalescence of the globules which
indicate a lack of uniformity of globules. As reported
earlier, an increase in the globule size is due to coalescence
phenomena, while a decrease in the size is due to leakage
of water from the internal to the external aqueous phase
[24]. Results from the microscopic and centrifugation
stability studies have been shown in Tables 3, 4 and 5.
Photomicrographs of multiple emulsion formulations
that have been kept at different storage conditions have
been shown in Figure 1.
Conductometric and pH analysis
Incorporating a conductometric tracer in the inner aqueous
phase of the primary emulsion is necessary to detect
any leakage from the internal to the external aqueous
phase of W/O/W emulsion. Measurement of conductivity
also provides the information about the entrapment of
active substances in the primary emulsion. The amount
of release is directly proportional to the amount of active
substance that is available in the external aqueous
phase and a rapid release therefore does not favor the slow
release of the active substance. No significant variation
in the conductivity was observed over 30 days of storage
period and at any of the temperature that was subjected