Continuous monitoring for cyanide in waste water with a galvanic hydrogen cyanide sensor using a purge system

A continuous monitoring system for cyanide with a galvanic hydrogen cyanide sensor and an aeration pump for purging was developed. Hydrogen cyanide evolved from cyanide solution using a purging pump was measured with the hydrogen cyanide sensor. The system showed good performance in terms of stability and selectivity. A linear calibration curve was obtained in the concentrating range from 0 to 15 mg dm³ of cyanide ion with a slope of - 0.24 μA mg^-1 dm^-3. The lower detection limit was 0.1 mg dm^-3. The 90% response time of the sensor system was within 3.5 min for a 0.5 mg dm^-3 cyanide solution, when the flow rate of the purging air was 1 dm³ min^-1. The system maintained the initial performance for 6 months in the field test. The developed galvanic sensor system was not subject to interference from sulfide and residual chlorine, compared with a potentiometric sensor system developed previously. The analytical results obtained by the present system were in good agreement with those obtained by the pyridine pyrazolone method. The correlation factor and regression line between both methods were 0.979 and Y = 2.30 x 10^-4 + 1.12X, respectively. This system was successfully applied for a continuous monitoring of cyanide ion in waste water.