Abstract: An electroanalytical electrode assembly includes an electrically conductive working electrode having a body of electrolyte material thereupon and separated from the analytical environment by a hydrophobic membrane. The membrane has an electrical conductivity greater than the electrical conductivity of the remainder of the measuring circuit and is selectably permeable for a preselected and ionic species, so as to provide a stable membrane potential. Use of an assembly of this type allows for placement of a reference electrode external of the membrane.

Abstract: Apparatus for measuring or detecting a chemical entity in a liquid sample, the apparatus including a first module operationally connected to a second module, the first module having a flow passage for the sample, the flow passage including a sensor for measuring or detecting the chemical entity and .Iadd.a .Iaddend.pump .[.means.]. for advancing the sample along the flow passage, the second module including .[.means.]. .Iadd.an actuator .Iaddend.for actuating the pump means, and the second module being connected to the first module via .[.connecting means.]. .Iadd.a connector .Iaddend.permitting disconnection of the first and second modules and connection of a replacement first module to the second module.