A new pH sensitive detector for flow-through potentiometry was developed on the basis of a graphite/quinhydrone composite electrode. The detector was constructed of two polymethyl methacrylate plates between which a 0.1 mm thick sensitive layer is situated. After drilling a hole through the plates, a ring of the sensitive layer is exposed to the solution stream. A conventional calomel reference electrode was placed downstream following the flow-through sensor. The response behavior in different electrolyte solutions was investigated. The detector shows a Nernstian behavior for injections of hydrochloric acid into a KCl background solution as well as for the steady state response in concentration step experiments using hydrochloric acid and buffer solutions. The response time is sufficiently short for FIA applications (T-95 between 3 and 5.4 s). The influences of flow rate and injection volume on the detector signal are discussed.