Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8994347 | Journal of Pharmaceutical Sciences | 2005 | 6 Pages |
Abstract
In our previous studies, surface analysis by inverse gas chromatography (IGC) at infinite dilution (zero coverage) was performed on four salmeterol xinafoate (SX) powdered samples, viz, two supercritical CO2âprocessed Form I (SXâI) and Form II (SXâII) polymorphs, a commercial granulated SX (GSX) raw material and its micronized product (MSX). Both GSX and MSX are also of the same Form I polymorph. To further probe the differences in surface properties between the samples, the present study has extended the IGC analysis to the finite concentration range of selected energy probes. The adsorption isotherms of the SX samples were constructed using (nonpolar) octane, (polar acidic) chloroform, and (polar basic) tetrahydrofuran as liquid probes. Type II adsorption isotherms with weak knees were observed with each probe for all SX Form I samples. The extents of probe adsorption by the samples at various relative pressures follow the rank order: SXâIIâ>âGSXâââMSXâ>âSXâI, indicating that the SXâI has fewer highâenergy adsorption sites than GSX and MSX. Type III isotherms were observed for SXâII with the two polar probes, indicative of weak adsorbate-adsorbent interactions. The additional information generated shows that IGC analysis at finite coverage is a valuable complementary tool to that at infinite dilution. © 2005 WileyâLiss, Inc. and the American Pharmacists Association J Pharm Sci 94:695-700, 2005
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Authors
Henry H.Y. Tong, Boris Y. Shekunov, Peter York, Albert H.L. Chow,