Validating AIM-Based Instrumentation and Associated Measurement Techniques - Good Cascade Impactor Practices, AIM and EDA for Orally Inhaled Products - page 343

for small upward shifts in fine particle fraction observed at 5 μ m aerodynamic

diameter with the FSI.
Further work is needed to understand the relative importance of both causes,
as well as to determine how much of the divergence between abbreviated and
full-resolution DPI-based measurements is formulation based and therefore
productspecific.

3. The Twin Impinger (Apparatus A in monograph 2.9.18 of the European
Pharmacopoeia) may become a suitable candidate AIM apparatus. It already has
only a single cut-point size of 6.4 m at 60 L/min [ 5 ]. Being an impingement

device, the potential for bias from bounce and re-entrainment are eliminated by
virtue of collecting the particles in the impingement fluid, as well as having the
intrinsic advantage that recovery of active pharmaceutical ingredient from the
impingement fluid can be achieved without further work-up in some cases.
Modifications to achieve a slight reduction in the cut point to 5

μ

m at a defined
flow rate in the range within which MDI and DPI testing, respectively, takes
place (30-100 L/min) appear to be feasible.
A better alternative might be to develop a reduced (say 2 or 3-stage) version
of the MSLI (Fig. 10.70 ), which also achieves avoidance of particle bounce and

μ

Fig. 10.70 Multistage liquid
impinger: a candidate for
abbreviation? ( Courtesy of
Copley Scientific Ltd. )