Combined ph and dissolved carbon dioxide gas sensor

Abstract

A combination pH and CO.sub.2 sensor employs separate sensors. Each sensor has a wire with an electrochemically active layer, an electrolyte layer and a membrane between the electrolyte layer and the fluid to be tested. Each electrolyte layer is constructed of a dried residue which can be easily stored and which must be rehydrated prior to the first use. The electrolyte layer in the pH sensor when hydrated forms an aqueous solution buffered against changes in pH due to changes in the dissolved CO.sub.2 concentration and is preferably formed of 2-(n-morpholino) ethanesulfonic acid, 2-(n-morpholino) ethanesulfonic acid - sodium salt and potassium chloride. The electrolyte layer in the CO.sub.2 sensor when hydrated forms an aqueous solution having bicarbonate ions and is preferably formed of polyvinyl alcohol, sodium chloride and sodium bicarbonate. The electrical potential at the pH sensor is proportional to the pH of the fluid. The electrical potential difference between the CO.sub.2 sensor and the pH sensor is proportional to the concentration of dissolved CO.sub.2 in the fluid. In the preferred embodiment the two sensors are formed in a sensor assembly with the fluid pumped through a channel. This invention is readily adaptable to a storage stable disposable assembly.