Patent ID: 7790006

Claim:
An amperometric sensor for measuring free chlorine in a solution, the free chlorine being in the form of hypochlorite ion and hypoclorus acid, the sensor comprising: a sensor body; an electrolyte disposed within the sensor body; a membrane coupled to the sensor body and adapted to pass hypochlorite ion and hypoclorus acid therethrough into the sensor body; a reference electrode disposed in the electrolyte; a porous working electrode disposed proximate the membrane, the porous working electrode being constructed from a noble metal; and a solid phase long-term pH stabilizer disposed in the electrolyte, the stabilizer being an acid selected from the group consisting of succinic acid, adipic acid, suberic acid and boric acid, having a solubility in water, at about 25 degrees Celsius, between about 1.2 Moles/liter and about 0.001 Moles/liter, the stabilizer acting to maintain the pH in the electrolyte at a level to cause substantially all hypochlorite ion passing through the membrane to become hypoclorus acid.