Particulate interactions between drug and lactose carrier in dry powder inhaler formulations are affected by the heterogenous energy distribution on the surface of the individual compounds. A new method based on Inverse Gas Chromatography at finite concentration is applied to study the energy heterogeneity of untreated, milled, and recrystallized lactose of similar particle size distribution. Energy distributions for the dispersive surface energy and the specific free energy of ethanol are obtained. Milling causes an increase in surface energy due to formation of amorphous regions. Untreated and recrystallized materials have similar surface energies at low surface coverages but show clear differences in energy distribution.
"An overview of the influence of particles size reduction over the surface properties of pharmaceutical ingredients by IGC. Pharmaceutical solid g d s Reference Acetaminophen " Trowbridge et al. (1998) Heng et al. (2006) Cefditoren pivoxil # Ohta and Buckton (2004) DL-propanolol hydrochloride " York et al. (1998) Felodipine " Chamarthy and Pinal (2008) Griseofulvine Chamarthy and Pinal (2008) " Feng et al. (2008) Otte and Carvajal (2011) # Otte et al. (2012) Ibipinabant " Gamble et al. (2012) Indomethacin " Planinsek et al. (2010) Lim et al. (2013) Lactose Ahfat et al. (2000) Feeley et al. (2002) Newell and Buckton (2004) " Thielmann et al. (2007) Shariare et al. (2011) Brum and Burnett (2011) Jones et al. (2012) Mannitol " Ho et al. (2012) Salbutamol sulfate " Ticehurst et al. (1994) Feeley et al. (1998) Salmeterol Xinofoate " Tong et al. (2001) (2006) Das et al. (2009) Sucrose Surana et al. (2003) " Hasegawa et al. (2009) Luner et al. (2012) Succinic acid " Luner et al. (2012) inhalation. Nowadays, dry powder inhalers (DPIs) are of great interest thanks to the absence of propellant and the stability of the formulation as a result of the dry state. "
"The reason for this discrepancy is that IGC is usually used at infinite dilution conditions at which n-alkanes preferentially probe the higher energy sites on the solid surface  . To probe the whole surface, Thielmann et al. developed the method of IGC at finite concentration conditions . Then, Ho et al. compared the values of d s measured by IGC at finite concentration conditions with those measured by the contact angle method, and they found that IGC also generated higher values in the case of heterogeneous solid surfaces compared to the contact angle method, but similar values in the case of homogenous solid surfaces . "
Journal of Chromatography A 07/2015; 1408. DOI:10.1016/j.chroma.2015.07.003 · 4.17 Impact Factor
"Despite the potential importance of heterogeneity profiles, until now, there has been little emphasis on the characterisation of the surface energy distribution of organic solids. Recent advances of IGC surface energy methodology allow for the determination of surface energy distribution  , from the adsorption isotherms of a series of n-alkanes at finite concentrations (Figure 1). "
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