Determination of N-acetyl-L-cysteine by flow-injection potentiometry

A multi-purpose tubular flow-through sensor was constructed with an AgI-based membrane. The membrane was prepared by pressing silver salts (AgI, Ag₂S) and powdered Teflon. This membrane was incorporated in the tubular flow-through sensor body. A 2-mm diameter hole was drilled through the center of the tubular sensor and the membrane, thus determining the active sensor volume of about 4 μL. The tubular sensor with reference electrode was placed into a complex flow-injection system and used for the flow-through determination of N-acetyl-L-cysteine, (NAC), in perchloric acid medium, pH = l. Linear dependence was established between the recorded signal height and the concentration of NAC in the injected sample. The recorded change in potential for a decade change in concentration, 62 mV {p (NAC)}^–1, in the concentration range from 1 × 10^–4 to 1 × 10^–1 mol L^–1, was based on the formation mechanism of the sparingly soluble deposit between silver and NAC on the surface of the sensitive part of the membrane. Received: 7 July 1997 / Revised: 22 September 1997 / Accepted: 26 September 1997