A method and system for collecting airborne particles and hydrating the collected particles for analysis. The airborne particles, which may be biological contaminants, are collected from a container containing one or more mailpieces. In the collection stage, a dry filter collection assembly is connected to the container and air is drawn out of the container through a dry filter. A hydration solution is then injected into the collection assembly to hydrate the collected particles. Part of the hydration solution containing the collected particles is caused to move out of the collection assembly to a test cartridge for further testing.