Validating AIM-Based Instrumentation and Associated Measurement Techniques - Good Cascade Impactor Practices, AIM and EDA for Orally Inhaled Products - page 307

Fig. 10.28 Andersen 8-stage impactors ( a ) viable (AVCI); ( b ) nonviable (ACI) [ Courtesy of
Westech Instrument Services Ltd. ( a ) and Copley Scientific Ltd. ( b ) ]

constructed easily from existing components of the full-resolution system. In the past
10 years since commercialization, the NGI has become increasingly used to charac-
terize OIPs, especially since its acceptance as a pharmacopeial apparatus for APSD
determinations (Apparatus 5 and 6 in Chap. 601 of the US Pharmacopeia, and appa-
ratus E in Chap. 2.9.18 of the European Pharmacopoeia—see Chap. 2 ) . Abbreviated
systems based on this impactor are either newly introduced units or involve modifica-
tion of a full-resolution impactor, which is discussed later in this chapter.
The fast screening impactor (FSI) is a newly introduced one-stage impactor
(Fig. 10.29 ), importantly with no “parent” full-resolution apparatus; although its
design is based on a modified NGI pre-separator [ 34 ]. With this abbreviated impac-
tor, large non-inhalable liquid boluses from nebulizing systems and powder boluses
in the case of DPIs are captured in a liquid trap, and the sample is then separated by
a fine-cut impaction stage whose d 50 is 5.0 μ m. A filter collector below the pre-

separator body collects the fine fraction.
The stage collection efficiency characteristics of four slightly different designs of
FSI insert having a nominal cut point of 5 m aerodynamic diameter have been

reported by Roberts and Romay [ 34 ] (Table 10.11 ), permitting the FSI to be oper-
ated in the flow rate range from 30 to 90 L/min, and therefore making it suitable for
DPI aerosol characterization, as well as with the other forms of OIP.
The sharpness of cut, given by the closeness of the geometric standard deviation
( GSD stage ) to unity (see Chap. 2 ), was excellent in all the cases for which data were
presented (the GSD stage of the insert developed to operate at 35 L/min was subse-
quently also confirmed to be close to 1.10). These values compare with values of
GSD stage in the range 1.1-1.4 for the NGI [ 35 , 36 ] intentionally designed to have
optimum performance in terms of size-fractionation and resolution capability [ 14 ].
There are now inserts manufactured with 5

μ

μ m cut point for use at 5 L/min intervals