Validating AIM-Based Instrumentation and Associated Measurement Techniques - Good Cascade Impactor Practices, AIM and EDA for Orally Inhaled Products - page 297

Fig. 10.18 FSA with annular
spacer stage (mFSA) used by
Keegan and Lewis ( From
[ 29 ]— used with permission )

impactor configurations are summarized in Fig. 10.19 . There was no difference
between the reported values for the glycerol-containing formulation regardless of the
impactor used ( p > 0.05). The addition of glycerol to a solution pMDI formulation
modulates the MMAD, increasing it from 1.3 m. This

effect may reduce impaction due to incomplete ethanol evaporation since the residual
droplets are larger. Significant differences ( p < 0.01) in the metrics obtained when the
ethanol concentration was at its highest (26%w/w) became evident between the
impactor systems.
The difference between the average BDP masses at each particle size fraction for
the ethanol-containing MDIs is reported in Table 10.8 . The residual values in this
table represent the absolute magnitude of the difference between FSA- and ACI-
measured values of each metric, expressed as a percentage and in micrograms.
Keegan and Lewis observed a consistent increase in the magnitude of the difference
between the FSA value and that calculated from ACI stage deposition as the ethanol
concentration in the formulation increased. Importantly, however, the inclusion of
the additional “spacer” stage in the FSA attenuated these divergence between FSA
and ACI-measured values of both CPM >5.0μm and FPM <5.0μm , as would be expected
from the earlier observations of Mitchell et al . [ 20 ]. However, this behavior was
offset by increases in divergence with values of EPM <1.0μm when the “spacer” stage
was included.
Figure 10.20 shows the effect of the “spacer” stage on deposition of BDP on the
collection plate of the first FSA stage in comparison with the calculated equivalent
from the full-resolution ACI (impaction stage mass less FPM <5.0μm ).

μ m (13% ethanol) to 2.8 μ