For simplicity, the Ag/AgCl reference electrodes were incorporated into a HPLC style and sized, screw thread (figure ). Alongside the Ag wire, a tube was inserted into the screw thread to allow any trapped air bubbles to be removed during filling, and was usually sealed during operation, i.e., no flow was observed out of the reference electrode port during sensing. To simplify the number of parts and designs, the same sized screw thread was used to insert other parts and components. As shown in figure (top right image), the screw thread was used for the inlet, outlets, reference electrodes and subsequent RPS materials.