GB5750-2006 provides that the concentration of sulfide in drinking water should not be higher than 0.02mg / L, free cyanide should not be higher than 0.05mg / L. Both ions have significant redox properties and are weak or unresponsive to suppress the conductance detection. Therefore, the amperometric ampere mode can be used to detect these two ions sensitively. Using Ag working electrode, Pt auxiliary electrode, Ag / AgCl reference electrode, sulfide and cyanide can be detected sensitively at a certain applied potential, and a higher signal to noise ratio is obtained. (Fluoride ions, nitrates, sulphates, etc.) or other differences in retention (such as sulfite, thiosulfate, etc.), and therefore may have a higher resistance to the presence of other interfering ions in the drinking water or to the ampere detector Selectivity.