Assessment of the need to coat particle collection cups of the NGI to mitigate droplet bounce when evaluating nebuliser-produced droplets.

The European Pharmaceutical Aerosol Group (EPAG) has been undertaking a series of investigations in support of developing robust methods for the droplet size analysis of nebuliser-produced aerosols for the proposed European Pharmacopoeia general chapter 2.9.44 covering preparations for nebulisation. The present two-centre study, which was designed to confirm whether or not coating the collection cups of the Next Generation pharmaceutical Impactor (NGI, the recommended impactor for the proposed monograph) is required, forms part of these investigations. The study evaluated NGI-measured aerodynamic droplet-size distributions of aerosols of a generic salbutamol solution for nebulisation generated by two different jet nebulisers. The results demonstrated that there was no indication of biased stage deposition when silicone oil was used to coat the impaction surfaces, as compared to uncoated surfaces. The conclusion was that there is no need to coat the NGI cups when nebulised products are investigated.