Coulometric microflow titrations with chemiluminescent and amperometric equivalence point detection - Bromimetric titration of low concentrations of hydrazine and ammonium

A coulometric flow titration with electrogenerated bromine was combined with chemiluminescent and amperometric flow detection to determine low concentrations of hydrazine and ammonium. Hydrazine can be precisely titrated in the range between 2 mu M and 1.1 mM I with chemiluminescence detection of the equivalence points with relative standard deviations between 1.9 and 0.4% (n=5, alpha=0.05). 60 nM is the lowest concentration of hydrazine, which can be titrated. Despite quenching the chemiluminescence ammonia concentrations lower than 0.5 mM do not influence the titration results. Between pH I and 7 hydrazine can be selectively titrated in the presence of ammonium. The sum of hydrazine and ammonia/ammonium was titrated at pH 8.3 with amperometric detection. Both hydrazine and ammonia/ammonium can be determined without calibration. The amperometric detection of the equivalence points is to be preferred in the presence of ammonia. Hydrazine and ammonia were titrated precisely in their mixtures and in concentration ranges between 20 mu M and 0.5 mM. Micromolar concentrations of hydrazine and ammonia/ammonium were determined precisely and accurately in spiked water samples. (C) 2000 Elsevier Science B.V. All rights reserved.