Effect of thiocyanate on nitrite estimation and the cleavage of nitrosamines.

Thiocyanate or bromide increased the colour formed by nitrite reacting with sulfanilic acid and naphthylethylenediamine. If the colour reagents were added together with thiocyanate (final concentration, M/10), the colour intensity was doubled. If sulfanilic acid was added three minutes before addition of naphthylethylenediamine, the relationship between nitrite concentration and colour production was more linear in the presence of thiocyanate. This effect was due to thiocyanate catalysing the diazotization of sulfanilic acid and inhibiting the reaction of nitrite with naphthylethylenediamine. Bromide and thiocyanate are similar in their catalytic effects on nitrosation, and hydrobromic acid in glacial acetic acid is an effective reagent for denitrosation of nitrosamine. Although thiocyanate catalysed denitrosation of nitrosamines, the effect was small except with nitrosomethylaniline, which had also been found to be denitrosated by sulfanilic acid. Thiocyanate could not be used generally for the destruction of nitrosamines; it was also found to be ineffective as an alternative to hydrobromic acid in the estimation of nitrosamines.