The development of dry powder inhalers (DPIs) and/or inhalation formulations is a laborious process which involves the determination of aerodynamic particle size distributions (aPSD), using full resolution impactors (i.e. Andersen Cascade Impactor (ACI) and the Next Generation Impactor (NGI)). Although developed to improve flexibility and precision, there is little information in the open literature regarding the benchmarking of the NGI with its predecessor, in their gravimetric form. Therefore, this work intends to compare both equipment and assess operational limits where the two techniques show good correlation. Additionally, characterization was also conducted with an abbreviated version of the NGI, the Fast Screening Impactor (FSI), to compare the results obtained via the three techniques (NGI, ACI, FSI) and, in this way, assess a potential full interchangeability.
The obtained results show that good correlations were found between the two full resolution impactors (NGI, ACI) when using fill weights of 20 mg. On the other hand, high fill weights (of 80 mg) were found to have a detrimental effect on the correlation, mostly due to an overload of the NGI apparatus. When comparing the FSI results with the corresponding full resolution results, a good correlation was found, in general; however, some loss of accuracy was noticeable, which translated into a reduced discriminative power, if in the presence of formulations of similar performance. Finally, all obtained results suggest that the use of gravimetric impactors are well suited for evaluating powders with a highly cohesive and adhesive nature, like the ones considered during the current work.