Method for Collection of Nebulized Proteins

Fine particle size fractions of nebulized solutions of small molecular weight drugs are typically captured dried on microfilters for subsequent drug characterization. This procedure normally does not lead to chemical modification of small molecules. However, it may cause adhesion and denaturation of proteins. To quantitate active, unmodified protein drugs in the fine size fractions of nebulized aerosols, we developed a method to overcome these problems. A sintered glass filter funnel was introduced downstream from the aerosol generator which produced a cloud containing droplets of an aqueous solution of protein at a rate of 7 L/min. The aerosol was drawn into the sintered glass filter together with 16-19 L/min of air pre-humidified at 47°C and collected in an ice-cooled filter flask. The humid dilution air was mixed with the aerosol in an attempt to induce condensation growth of the droplets. By increasing the droplet size, an increase in impaction collection efficiency should result. To test whether this arrangement reduced the fraction of droplets that escaped impaction, a glass fiber filter was placed at the exhaust from the aerosol line. The weight of the dry material collected on this filter was only 2% of the initial load when the humid air was used. In addition, the presence of the humid air resulted in an overall aerosol recovery of 98%. Analysis of the collected protein indicated full retention of its activity and structural integrity. This setup will most likely enable quantitative collection of other aqueous protein aerosols that can then be subjected to biochemical analysis.