AAPS PharmSciTech

, Volume 10, Issue 1, pp 252–257 | Cite as

The Abbreviated Impactor Measurement (AIM) Concept: Part II—Influence of Evaporation of a Volatile Component—Evaluation with a “Droplet-Producing” Pressurized Metered Dose Inhaler (pMDI)-Based Formulation Containing Ethanol as Cosolvent

  • J. P. Mitchell
  • M. W. Nagel
  • V. Avvakoumova
  • H. MacKay
  • R. Ali
Research Article


The abbreviated impactor measurement (AIM) concept is a potential solution to the labor-intensive full-resolution cascade impactor (CI) methodology for inhaler aerosol aerodynamic particle size measurement. In this validation study, the effect of increasing the internal dead volume on determined mass fractions relating to aerodynamic particle size was explored with two abbreviated impactors both based on the Andersen nonviable cascade impactor (ACI) operating principle (Copley fast screening Andersen impactor [C-FSA] and Trudell fast screening Andersen impactor [T-FSA]). A pressurized metered dose inhaler-delivered aerosol producing liquid ethanol droplets after propellant evaporation was chosen to characterize these systems. Measures of extrafine, fine, and coarse particle mass fractions from the abbreviated systems were compared with corresponding data obtained by a full-resolution ACI. The use of liquid ethanol-sensitive filter paper provided insight by rendering locations visible where partly evaporated droplets were still present when the “droplet-producing” aerosol was sampled. Extrafine particle fractions based on impactor-sized mass were near equivalent in the range 48.6% to 54%, comparing either abbreviated system with the benchmark ACI-measured data. The fine particle fraction of the impactor-sized mass determined by the T-FSA (94.4 ± 1.7%) was greater than using the C-FSA (90.5 ± 1.4%) and almost identical with the ACI-measured value (95.3 ± 0.4%). The improved agreement between T-FSA and ACI is likely the result of increasing the dead space between the entry to the induction port and the uppermost impaction stage, compared with that for the C-FSA. This dead space is needed to provide comparable conditions for ethanol evaporation in the uppermost parts of these impactors.

Key words

cascade impactor inhaler testing particle evaporation particle size distribution 



Andersen cascade impactor


abbreviated impactor measurement


active pharmaceutical ingredient


aerodynamic particle size distribution


beclomethasone dipropionate


cascade impactor


Copley fast screening Andersen impactor


coarse particle fraction (based on impactor-sized mass)


extrafine particle fraction (based on impactor-sized mass)


fine particle fraction (based on impactor-sized mass)


mass median aerodynamic diameter of impactor-sized aerosol


pressurized metered dose inhaler


Trudell fast screening Andersen impactor



The authors acknowledge the support of Copley Scientific Ltd. for the C-FSA and the advice and support of Mark Copley and Daryl Roberts (MSP Corp., St. Paul, MN, USA) during the development and execution of this investigation. They also wish to thank Steven Stein (3M Drug Delivery Systems, St. Paul, MN, USA) for the supply of ethanol-sensitive paper as well as for additional discussions as the work progressed.


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Copyright information

© American Association of Pharmaceutical Scientists 2009

Authors and Affiliations

  • J. P. Mitchell
    • 1
  • M. W. Nagel
    • 1
  • V. Avvakoumova
    • 1
  • H. MacKay
    • 1
  • R. Ali
    • 1
  1. 1.Trudell Medical InternationalLondonCanada

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