Polystyrene microsphere spray standards based on CFC-free inhaler technology

Metered pressurized sprays were formulated containing polystyrene microspheres (PSM) suspended in 5% w/w ethanol in 1,1,1,2-tetrafluoroethane (HFA 134a). Suspensions with defined number concentrations, packaged in pressure-resistant glass containers, and fitted with specified 50-microL metering values and actuators were sonicated and fired (as if they were metered dose inhalers or MDIs). Following propellant evaporation, PSM dispersions in air containing > 98% singlets resulted from actuation of 3, 5, and 8 microns PSM suspensions containing 0.00125% w/w 3 microns, 0.05% w/w 5 microns or 0.3% w/w 8 microns PSMs, 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. Over a period of 6 months storage, these formulations produced reproducible PSM aerosols with known aerodynamic properties useful for calibration purposes.