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Abstract
The potential of the ammonia selective electrode was plotted versusiog [NH4C1] in solutions to which a tenfold excess (v/v) of 10 M NaOH was added. ‘Eisenman plots’ were obtained in the presence of ten different aliphatic amines. Corresponding potentiometric selectivity coefficients (PSC) were evaluated. These correlated as follows with the dissociation constants of ammonia (K') and of the relevant amine (K): log PSC = pK'a-pKa. Accordingly, deviations from correct ammonia electrode potentials increased with amine base strength. This effect can be compensated by adjusting the internal solution of the ammonia electrode to match the composition of the so-called ‘total basic volatile nitrogen’ in the conventional sample distillate.