Use of the aerosizer (R) 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 meas urements offers a significant advantage in terms of user convenience compar ed with aerodynamic particle size analysis by cascade impactor or multi-sta ge liquid impinger. However, the present study has highlighted a limitation in its use in the measurement of aerosols from many types of pressurized m etered-dose inhaler (pMDI) in which the measured total number concentration exceeds about 10(10) particles m(-3). The causes are complex, but appear p rimarily to be associated with the loss of electrical signals from individu al particle-detection beam interactions, associated with timer insensitivit y of the signal correlation system. This phenomenon occurs where several pa rticles 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 o f portions of the data where the AUTOCOMBINE feature is used to create the full size distribution from the low and high detection sensitivity sub-rang es. (C) 1999 Elsevier Science Ltd. All rights reserved