Aerodynamic particle size analysis of aerosols from pressurized metered-dose inhalers: comparison of Andersen 8-stage cascade impactor, next generation pharmaceutical impactor, and model 3321 Aerodynamic Particle Sizer aerosol spectrometer - Mitchell, J P; Nagel, M W; Wiersema, K J; Doyle, C C (AAPS PharmSciTech, 2003)