Sequential determination of free and total cyanide by flow injection

This study presents a flow injection system for the sequential determinatio n of free (CN-) and total (CN- + HCN) cyanide using a potentiometric method which employs two different processes for the determination of these two c hemical species. The first process is based on direct detection of CN- usin g an ion-selective electrode for cyanide. In the second process, the sample is mixed with acid, and the released HCN is transferred across a PTFE memb rane. The flow system employs three solenoid valves, a gar diffusion chambe r, an ion-selective electrode, a potentiometer, and a computer with an AID conversion card. A Turbo Pascal(R) computer program automatically performs all the steps involved in data acquisition and processing. The standard dev iation far the results obtained with the proposed method was 0.5%.