Pulsating potentiometric titration technique for assay of dissolved oxygen in water at trace level

A simple but high performance potentiometric titration technique using pulsating sensors has been developed for assay of dissolved oxygen (DO) in water samples down to 10.0 μg L−1 levels. The technique involves Winkler titration chemistry, commonly used for determination of dissolved oxygen in water at mg L−1 levels, with modification in methodology for accurate detection of end point even at 10.0 μg L−1 levels DO present in the sample. An indigenously built sampling cum pretreatment vessel has been deployed for collection and chemical fixing of dissolved oxygen in water samples from flowing water line without exposure to air. A potentiometric titration facility using pulsating sensors developed in-house is used to carry out titration. The power of the titration technique has been realised in estimation of very dilute solution of iodine equivalent to 10 μg L−1 O2. Finally, several water samples containing dissolved oxygen from mg L−1 to μg L−1 levels were successfully analysed with excellent reproducibility using this new technique. The precision in measurement of DO in water at 10 μg L−1 O2 level is 0.14 (n = 5), RSD: 1.4%. Probably for the first time a potentiometric titration technique has been successfully deployed for assay of dissolved oxygen in water samples at 10 μg L−1 levels.