Use of the aerosizer® aerodynamic particle size analyzer to characterize aerosols from pressurized metered-dose inhalers (pMDIs) for medication delivery

The Aerosizer(R) aerodynamic particle size analyzer is widely used for the rapid assessment of medical aerosols. Its real-time capability to make measurements offers a significant advantage in terms of user convenience compared with aerodynamic particle size analysis by cascade impactor or multi-stage liquid impinger. However, the present study has highlighted a limitation in its use in the measurement of aerosols from many types of pressurized metered-dose inhaler (pMDI) in which the measured total number concentration exceeds about 10(10) particles m(-3). The causes are complex, but appear primarily to be associated with the loss of electrical signals from individual particle-detection beam interactions, associated with timer insensitivity of the signal correlation system. This phenomenon occurs where several particles are present simultaneously within the measurement zone. Subsequent processing of the time-of-flight data may result in significant distortion of the reported size distribution, including in extreme cases the absence of portions of the data where the AUTOCOMBINE feature is used to create the full size distribution from the low and high detection sensitivity sub-ranges. (C) 1999 Elsevier Science Ltd. All rights reserved