title: Characterising surface energy of pharmaceutical powders by inverse gas chromatography at finite dilution.
abstract: OBJECTIVE
  The objectives of this project were the use of surface energy distributions in: distinguishing the effects of magnesium stearate on the surface energy of lactose processed by two methods: mixing in a Turbula and mechanofusion; characterising surface energy of materials before and after micronisation; and understanding surface energy changes of micronised lactose before and after storage at high relative humidity (RH).
  
  
  METHODS
  Heptane, octane and nonane were used to determine nonpolar surface energy, and dichloromethane and ethyl acetate were used to determine polar surface energy in inverse gas chromatography at finite dilution.
  
  
  RESULTS
  The total surface energy of lactose decreased more after mechanofusion with magnesium stearate than mixing in Turbula. The nonpolar surface energy of indometacin increased while polar and total surface energies decreased after micronisation. The nonpolar, polar and total surface energies and work of cohesion of micronised lactose decreased after storage at 75% RH for three months.
  
  
  CONCLUSIONS
  The surface energy distributions determined at finite dilution successfully distinguished and revealed more information than infinite dilution on surface energy changes in materials undergoing different pharmaceutical processes such as mixing, mechanofusion, micronisation and storage at high RH.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia. shyamal.das@monash.edu
authors.forename: Shyamal C
authors.initials: SC
authors.lastname: Das
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Stewart
mesh_terms: D000280:Administration, Inhalation; D000336:Aerosols; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage / Q000032:analysis / Q000737:chemistry*; D055598:Chemical Phenomena; D002849:Chromatography, Gas; D004339:Drug Compounding; D016503:Drug Delivery Systems; D004356:Drug Storage; D058995:Dry Powder Inhalers; D005079:Excipients / Q000032:analysis / Q000737:chemistry*; D006801:Humans; D007213:Indomethacin / Q000008:administration & dosage / Q000032:analysis / Q000737:chemistry*; D007785:Lactose / Q000032:analysis / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D009994:Osmolar Concentration; D010316:Particle Size; D011208:Powders; D012997:Solvents / Q000737:chemistry; D013229:Stearic Acids / Q000032:analysis / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D000336:Aerosols; D000894:Anti-Inflammatory Agents, Non-Steroidal; D005079:Excipients; D011208:Powders; D012997:Solvents; D013229:Stearic Acids; C031183:stearic acid; D007785:Lactose; D007213:Indomethacin