Determination of Dissolved Oxygen in Water by Micro-Weighing-Titration with a Polythene Capillary Burette

In the iodometric titration of dissolved oxygen in water,weighing titration with Na2S2O3 standard solution was applied.A self-made polythene capillary burette was used in the titration instead of the complex and precise weighing titration deviced specified in the standard GB 10738-1989.The polythene capillary burette was filled with standard solution of Na2S2O3,and the total mass of the burette and titrant was weighed on a precise electronic balance before and after the titration using starch as indicator.Amount of dissolved oxygen in the sample was calculated from the mass of Na2S2O3 standard solution according to the formula given in the paper.One drop of titrant from the capillary burette was qualified to have the mass in the range from 0.005-0.010 g.Relative deviation of the titration process was controlled around 1.0%.Titration of the proposed method was made on a micro scale,thus resulting less comsuption of reagents,more rapid and convenient in operation,as well as better accuracy and precision than the GB standard method.Values of RSD′s (n=7) obtained in analysis of 4 water samples were ranging from 0.18%-0.66% which were smaller than those obtained by the GB method (0.43%-1.26%).