Abstract: A replaceable cap assembly for use with an electrochemical analysis electrode that includes an electrode body and an ion selective portion at an end of the body comprises a housing component for releasable attachment to the electrode body and a membrane securing component. The housing component has a cavity for receiving the ion selective portion when the housing is attached to the electrode body and a port in its end wall. A selectively permeable membrane that is disposed between two juxtaposed annular sealing elements extends across the port, and the membrane-annular sealing element assembly is fastened in place with the securing component such that the juxtaposed sealing members are compressed against the membrane to seal the port with the membrane being seated against the ion selective portion of the electrode when the cap assembly is attached to the electrode body.