Determination of the surface energy distributions of different processed lactose.
ABSTRACT 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.
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ABSTRACT: Purpose: This study determined total surface energy distributions using an Inverse Gas Chromatography (IGC) to understand the de-agglomeration of fine lactose powders commonly used in dry powder inhaler formulations. Methods: The particle size distribution (PSD) of two lactose samples, Lactohale 300 ® (Lac A) and micronized lactose (Lac B), were determined by laser diffraction in liquid media, and the PSD of the aerosolised plume dispersed from a Rotahaler ® was determined by a Spraytec ® at air flow rates of 30-180 l/min. The total surface energy distribution profiles were determined at finite dilution by IGC. Results: The mean diameters of Lac A and Lac B were 2.9 ± 0.2 and 3.9 ± 0.3 µm, respectively. The total surface energy of Lac A was lower than Lac B over around 3% of surface coverage. De-agglomeration profiles of the lactose samples showed that, while the percent volume less than 5.4 µm of Lac A was greater than Lac B at the air flow rates up to 90 l/min, the de-agglomeration capacity of Lac B was higher at flow rates of 120-180 l/min. These data were consistent with a surface energy and particle size-driven de-agglomeration at low flow rates and a more structure-driven de-agglomeration at higher flow rates. Conclusion: The study reinforced the importance of packing fraction, particle size and surface energy in understanding de-agglomeration of cohesive powders. However, where particles were strongly bound to give non-dispersible agglomerates, de-agglomeration was more reliant on powder structures than on surface energy.
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ABSTRACT: Surface area and surface energy of pharmaceutical powders are affected by milling and may influence formulation, performance and handling. This study aims to decouple the contribution of surface area and surface energy, and to quantify each of these factors, on cohesion.Pharmaceutical Research 07/2014; · 3.95 Impact Factor
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ABSTRACT: Inverse gas chromatography (IGC) is a versatile, powerful, sensitive and relatively fast technique for characterizing the physicochemical properties of materials. Due to its applicability in determining surface properties of solids in any form such as films, fibres and powders of both crystalline and amorphous structures, IGC became a popular technique for surface characterization, used extensively soon after its development. One of the most appealing features of IGC that led to its popularity among analytical scientists in early years was its similarity in principle to analytical gas chromatography (GC). The main aspect which distinguishes IGC experiments from conventional GC is the role of mobile and stationary phases. Contrary to conventional GC, the material under investigation is placed in the chromatographic column and a known probe vapour is used to provide information on the surface. In this review, information concerning the history, instrumentation and applications is discussed. Examples of the many experiments developed for IGC method are selected and described. Materials that have been analysed include polymers, pharmaceuticals, minerals, surfactants, and nanomaterials. The properties that can be determined using the IGC technique include enthalpy and entropy of sorption, surface energy (dispersive and specific components), work of co/adhesion, miscibility and solubility parameters, surface heterogeneity, glass transition temperature, and specific surface area.Advances in Colloid and Interface Science. 10/2014; 212:21.