An interesting fact was found that the nitrite ion reacted not only with ethylenediaminetetraacetic acid (EDTA) but with most of the amines to liberate a cyanide ion, the concentration of which frequently exceeded the regulation limit provided by the Japanese law (source limit : 1ppm, environmental limit : 0.1ppm). Therefore, in the case of waste water containing a nitrite ion, a denitriting agent should be added before distillation of the sample solution. Only ammonium sulfamate was suitable as a denitriting agent, because sulfanilamide reacted with the nitrite ion to form a cyanide ion, sodium azide reacted with a cyanide ion to decompose the cyanide ion itself, and urea did not eliminate the nitrite ion sufficiently.