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Abstract
This study investigated the relationship between surface energy of micronized lactose,
coarse lactose and salmeterol xinafoate and dispersibility from a mixture after storage
at 75% RH. Surface energies, dispersibility, morphology, and the presence of amorphous
domains were determined by inverse gas chromatography, twin stage impinger, scanning
electron microscope and dynamic vapour sorption, respectively. The fine particle fraction
of mixture decreased significantly in 4 weeks (P<0.05), reaching a static level in
3 months. Amorphous content was not detected in the micronized lactose, coarse lactose
and salmeterol xinafoate. After conditioning stored samples at 75% RH for 2h, dispersive
surface energy of both micronized and coarse lactose significantly decreased (P<0.05),
while the polar surface energy of all significantly increased (P<0.05) resulting in
significant increase in total surface energy after storage. After conditioning stored
samples at 0% RH for 2h, no significant difference was observed in any surface energy
parameter. This study concluded that the total surface energy increased during storage
at high RH due to the adhered surface moisture. The mechanism of decreased dispersibility
was related to increased capillary/solid bridging interactions and to possible increased
interaction of contiguous particles due to increased polar surface energy.