The use of inverse gas chromatography for the study of lactose and pharmaceutical materials used in dry powder inhalers.

Inverse gas chromatography (IGC) is a sensitive technique for the measurement of powder surface properties, especially surface energetics. Given the importance of these characteristics to the performance of dry powder inhaler formulations (DPIs), it is unsurprising that IGC has been applied to the study of these systems. Monitoring batch-to-batch variation and the effects of processing steps are established uses of IGC in this field and the relevant studies are discussed. A less established use of IGC is for the prediction of DPI performance. Although some groups have found a negative relationship between the dispersive surface energy of one formulation component and fine particle delivery, such studies often have a number of limitations. More complex approaches have failed to produce consistent results. Further, more carefully designed, studies are required in this area. In the final section of this article, some areas for on-going research are discussed, including the need to critically assess the best method for the calculation of the specific free energy of adsorption with pharmaceutical materials.