Importance of the impaction on agar surface.
Effect of jet velocity, nozzle size, nozzle distance from the agar surface, quality of medium, volume of medium inside the culture, expiration date of the plate, moisture content and sterility of the medium, temperature should be considered to obtain the optimization of these variables. These facts are determinative to obtain an efficient design of a microbial air sampler.
ISO-14698 standard mentions that impaction velocity should be less than 20 metres per second.
No air sampling device is perfect for all particles of different dimensions. Different organisms may be more robust than others and sizes vary widely so any design of sampling head can be no more than the best possible compromise.
An important aspect of the impaction on the agar surface is total number and the diameter of the holes in the aspirating head.
All these variables were considered in the development and production of the microbial air sampler TRIO.BAS.