Precise determination of hypochlorite in commercial bleaches with established traceability using automatic potentiometric titration

A measurement procedure is proposed for precisely determining hypochlorite in commercial bleaches, with established traceability and a full description of its uncertainty sources. The procedure is based on automatic volumetric titration with potentiometric detection and was evaluated in the analysis of several commercial bleach samples, with Na-hypochlorite mass fractions in the range 0.002-0.027 g g(-1), with an average expanded uncertainty (k = 2) of 0.00027 g g(-1) and an average relative standard deviation between measurement triplicates of 0.36 %. Compared with a standard procedure based on manual volumetric titration with visual colorimetric detection, the improved procedure produced equivalent results with a lower average expanded uncertainty (0.00029 g g(-1) as compared to 0.0015 g g(-1) for the standard procedure). This was related to better precision of the volume measurement using an automatic buret and to better precision of the titration endpoint determination using potentiometric detection. Compared with other studies reported in the literature, the improved procedure presented a lower average relative standard deviation between measurement replicates (0.36 % as compared to 1.00-11.53 %).