Validating AIM-Based Instrumentation and Associated Measurement Techniques - Good Cascade Impactor Practices, AIM and EDA for Orally Inhaled Products - page 299

Fig. 10.20 Mass BDP deposited on stage 1 of the FSA configurations compared with the equiva-
lent mass deposited in the ACI ( n = 3; ±SD). mFSA modified FSA as described above ( From [ 28 ]—
used with permission )

formulations with ethanol concentrations >8% w/w. They suggested that the inclusion
of a “spacer” stage may help to attenuate some differences between the FSA and
ACI. However, it is likely that the magnitude of the effect will be formulation/
device specific.
Keegan and Lewis concluded that, in general, the FSA may provide representa-
tive values for key particle metrics that are not significantly different from the
full-resolution ACI for solution pMDI formulations. If it can be used, this abbrevi-
ated impactor offers a tool that eliminates the need for post-analysis data processing
to obtain key metrics when screening formulations.
The outcomes from all of the work reported in this section reinforce the recom-
mendation that the implementation of an AIM-based method should always be
preceded by some form of validation study with the particular products of interest,
using an appropriate full-resolution CI as the benchmark technique.

10.6 Assessing the Performance of AIM Systems

Based on the Andersen Viable Cascade Impactor

The Andersen viable cascade impactor (AVCI) is the earliest version of the Andersen
multistage CIs to be developed [ 30 ]. It is similar in operating principle to the nonvi-
able ACI, with the important exception that the stage wells are larger so that they
can each accommodate a Petri dish instead of a collection plate [ 31 ]. The Westech
fine particle dose impactor (Westech Instrument Services, Upper Stondon, Beds.,
UK) was designed as a simple two-impaction stage and filter sampler for the rapid
determination of fine particle mass from pMDIs at 28.3 L/min (Smurthwaite MJ
(2012) Westech instrument services, UK, personal communication). The design is
based on an abbreviated AVCI (Fig. 10.21 ) but incorporates some new design features