A new approach to characterise pharmaceutical aerosols: Measurement of aerosol from a single dose aqueous inhaler with an optical particle counter

An in-line sampling system with dilution units for aqueous droplet aerosols from single dose inhalers (Berodual Respimat®, Boehringer Ingelheim Pharma GmbH & Co. KG, Germany) for an optical particle counter is described. The device has been designed to interface with a white light aerosol spectrometer (welas® digital 2100, Palas® GmbH, Germany) that allows the time-resolved measurement of highly concentrated aerosols. Performance of the sampling system with regard to the measured particle size distribution (PSD) is compared to Next Generation Impactor (NGI) and to laser diffraction measurements (Sympatec Inhaler and open bench). Optimal settings of the sampling system lead to PSDs that correspond well to those measured by the evaporation minimising NGI approach (15 L/min, cooled) and laser diffraction. The better accuracy of the new dilution unit in presence of an additional aerosol sampling filter in comparison to a previously described aerosol sampling system is shown for different settings of the sampling system. This allows a more precise quantification of the delivered drug amount which is also well correlated to the aerosol volume measured by the welas® system. In addition, using time-resolved welas® measurements provides insight into droplet size, evaporation and size changes of aerosol clouds delivered by liquid inhalers.