Next Generation Pharmaceutical Impactor: A new impactor for pharmaceutical inhaler testing. Part III. Extension of archival calibration to 15 L/min

An extension of the archival calibration of the recently developed 30-100-L/min seven-stage impactor, the Next Generation Pharmaceutical Impactor (NGI), has been undertaken at 15 L/min. The NGI stage cut sizes are 0.98-14.1 μm aerodynamic diameter at this flow rate. This 15-L/min calibration was motivated by the desire to sample the entire aerosol produced by a nebulizer when tested in accordance with a new international standard developed by the Comité Européen de Normalisation (CEN), as well as the need to test various types of inhalers at flow rates lower than 30 L/min for pediatric applications. Measurements were undertaken with monodisperse oleic acid droplets in the range of 0.7-22 μm aerodynamic diameter following a procedure established in the original 30-100-L/min calibration study. The NGI was found to be effective for particle size separation at 15 L/min. Users should decide the most applicable configuration that meets their needs, based on the following recommendations: (1) the pre-separator should not normally be used, as its performance is significantly degraded by the influence of gravity, resulting in interference with stage 1; and (2) a filter should be inserted below the micro-orifice collector (MOC), as the size corresponding to 80% collection efficiency of the MOC becomes excessively large with decreasing flow rate, so that this component becomes ineffective as a means of collecting fine particles that penetrate beyond stage 7.