Precise and sensitive determination of nitrite by coulometric backtitration under flow conditions

A novel method performing for coulometric backtitrations in flow channels was developed, which was applied for the precise and sensitive determination of low concentrations of nitrite. Under acid conditions nitrite is reacting stoichiometrically with hydrazine, the remained excess of which is backtitrated with electrogenerated bromine. The titration course is recorded either amperometrically or chemiluminometrically. Hydrazine can be determined precisely and accurately in the range between 0.1 mu M and 1 mM without calibration. Nitrite is reduced by hydrazine according to the reaction 2 NO2- + 2 H+ + NH2-NH2--> N2O + N-2 + 3 H2O. Applying the amperometric and the chemiluminometric end-point location nitrite was determined accurately and precisely in the ranges 0.25-65 mu M and 0.10-50 mu M, respectively. The method was applied to the determination of nitrite in tap and river water.