Merck offers the most complete and accurate line of microbial air monitoring systems available. The MAS-100 Microbial Air Monitoring Systems are high-performance instruments which are based on the principle of the Andersen air sampler. Air is aspirated through a perforated lid, and impacted onto the surface of growth media in a standard 90 mm Petri dish or 60 mm contact plate. Microorganisms impact the culture media and the colonies are counted after a proper incubation period. The system measures the inflow of air and regulates the aspirated volume to a constant value of 100 liters/min. All MAS-100 air samplers comply with the guidelines of the ISO 14698 part 1 and part 2.