Study on cyanide determination by pyridine – Pyrazole reagent and its application to evaluate some cyanide contaminated wastewater resources in Hanoi

The Cyanide compounds have been listed as one of the toxic pollutants that are usually released into environment. A study on cyanide analysis has been devised to determine the total cyanide concentration in wastewater. This work determines the concentration of total cyanide in water and wastewater collected in some metal plating factories in Hanoi. The determination of cyanide (simple CN-) is based on the chlorination of cyanide and the subsequent reaction of the product with a mixed solution of pyridine – pyrazolone to form a stable color complex. Therefore, before chlorination of cyanide, the all cyanide compounds present in samples must be broken down by an acid reflux and distillation. The cyanide distillation also removes certain interferences from water samples. The cyanide concentration in the samples was determined by measuring absorbance at λmax = 614 nm in a suitable experimental condition  such as solution pH = 6.87, chloramine -T volume = 0.5 mL, pyridine – pyrazalone reagent solution = 3.0 mL, the complex forming time = 20 min. The LOD and LOQ of the method were established being 5.1x10-3 mg/L, 0.017 mg/L respectively. The method was applied to determine cyanide in wastewater of some metal plating factries in Hanoi, Vietnam.