Photometric microtitrations VIII.* Mercurimetric determination of cyanide using Naphthylazoxine 6S as indicator

Naphthylazoxine 6S was evaluated as a suitable metal indicator for the determination of cyanide in the concentration range 5x l ( )~ 4 to l x x K)"" mol dm" The use of photometric indication permitted titration with a dilute standard solution of mercury(II) Perchlorate (с = 0.001 mol dm 3 to 0.01 mol dm" ). Under optimum conditions (pH range 5.0 to 5.5, /«0.05 mol dm", c(ind)= K)" mol dm" 3 ; Л = 530 nm), precise results were obtained ( s r / % ^ 1). A thin layer of paraffin oil on the surface prevented loss of HCN during titration so that systematic deviations, with respect to the reference Liebig—Déniges titration with turbidimetric indication, were insignificant ( < 1 %) . Cyanide can be titrated in presence of an equal amount of chloride or thiocyanate (at p H « 6 ) ; bromide interferes, while iodide is titrated with cyanide.