In relation to carrying out research the studying of the aerodynamic particle size distribution of various active ingredients in DPI and MDI, there is need for using smaller and specialist cascading impactor. Therefore it has been found much more effective in using fewer stages and there are impactors with 3 or 4 stages which can work with different active ingredients as manufactured by different pharmaceutical companies.

Instead of using ACI(8 stage) or Westech 7 which consist of 7 stages it is often good practice to use these specialist impactors which are known as FPD or AIM impactors.

This often consists of 3-4 stages. Another advantage of using these impactors, it can work with different flow rate and this can be controlled by the critical flow controllers.

Please see US or Europe pharmacopoeia for more details.