Abstract: A gaseous or liquid sampling collection unit designed to prevent loss of any of the matter collected and designed to prevent the accidental or intentional loss of all or part of the amount of matter collected, consisting of a filter capsule comprising a shield, and a filter, a two piece cassette containing said capsule consisting of an upper member and a close fitting lower member wherein the capsule is positioned between the upper and lower members of said cassette, the upper member of said cassette containing a valving arrangement permitting a unidirectional flow and, a tamper proofing plate preventing the accidental or intentional interference with the collection function.