Measuring charge and mass distributions in dry powder inhalers using the electrical Next Generation Impactor (eNGI)

The electrical Next Generation Impactor (eNGI) was assessed against the electrical low-pressure impactor (ELPI) and next generation impactor (NGI) for its capability to characterise particle size and electrostatic charge properties of dry powder inhaler (DPI) formulations. Following assessment, the relationship between inhalational air flow rate and drug powder charge was explored using the eNGI. At a vacuum flow rate of 30L/min, doses of Pulmicort (budesonide 400 microg) and Bricanyl (terbutaline 500 microg) were dispersed into the ELPI, NGI and eNGI, from which particle size profiles and charge profiles were ascertained. Further doses of Pulmicort and Bricanyl were fired into the eNGI at vacuum air flow rates of 45, 60, 75 and 90 L/min, and the resultant size and charge profiles were determined. Particle size profiles at 30 L/min were found to be comparable between the NGI and eNGI, while charge profiles were comparable between the eNGI and ELPI. As air flow rate increased from 30 to 90 L/min, in vitro aerosol performance improved before reaching a peak at 45 L/min (Pulmicort) and 60 L/min (Bricanyl). Net charge also increased with flow rate, the cause of which may be a combination of increased turbulence and aerosol performance. This study demonstrates that the eNGI is capable of electrostatic and particle size characterization of commercial drug-only DPI products.