Microanalysis system for pO2, pCO2, and pH constructed with stacked modules

A miniaturized analysis system for online monitoring of pO₂, pCO₂, and pH was constructed by stacking a reference electrode module, a sensing module, and a sampling module. The liquid-junction reference electrode module used durable thin-film Ag-AgCl electrodes with pinholes to use an internal solution saturated with KCl. A Clark-type pO₂ sensor, a Severinghaus-type pCO₂ sensor, and an indicator electrode for a pH sensor were integrated on a sensing module. The sampling module used reversible growth or shrinkage of a hydrogen bubble on a platinum black working electrode. The volume change of the gas was converted to the movement of the solution in a flow channel reproducibly by a silicone rubber diaphragm. An external solution could be introduced into the system successfully by the sampling mechanism. Clear responses were observed with the three sensors upon sampling of standard solutions. Calibration plots were linear in clinically important ranges for the respective analytes.