Abstract: A replaceable cartridge assembly for use with electrochemical analysis apparatus includes a housing of electrically insulating material that defines an annular electrolyte chamber with coupling structure at one end of the housing and a chamber port at the other end of the housing. A selectively permeable membrane extends across the port in sealing relation thereto. An elongated guide channel within the housing is surrounded by the electrolyte chamber and receives a cooperating connector stem that carries a socket-temperature sensor assembly. A cathode electrode projects coaxially upwardly from the end wall of the guide channel into the stem socket and the lower portion of the cathode electrode extends through the guide channel end wall such that its tip is exposed to the membrane. An anode electrode is disposed in the electrolyte chamber with an external contact surface adjacent the coupling structure.