Polystyrene microsphere spray standards based on CFC-free inhaler technology

Metered pressurized sprays were formulated containing polystyrene microsphe res (PSM) suspended in 5% w/w ethanol in 1,1,1,2-tetrafluoroethane (HFA 134 a). Suspensions with defined number concentrations, packaged in pressure-re sistant glass containers, and fitted with specified 50-mu L metering values and actuators were sonicated and fired (as if they were metered dose inhal ers or MDIs). Following propellant evaporation, PSM dispersions in air cont aining >98% singlets resulted from actuation of 3, 5, and 8 mu m PSM suspen sions containing 0.00125% w/w 3 mu m, 0.05% w/w 5 mu m or 0.3% w/w 8 mu m P SMs, respectively. Spray characteristics from these systems depended on PSM concentration, PSM size, PSM source, and actuator dimensions. Adhesion of suspended PSMs to the internal glass surfaces of the containers were easily reversed by sonication but not prevented by a wide range of surfactants. O ver a period of 6 months storage, these formulations produced reproducible PSM aerosols with known aerodynamic properties useful for calibration purpo ses.