A modified Winkler's method for determination of dissolved oxygen concentration in water: Dependence of method accuracy on sample volume

A modification to the standard Winkler's method (WM) for measurement of dissolved oxygen (DO) concentration in aqueous samples enabled DO measurements in 1 mL sample volume. However, advanced statistical analysis indicated that the proposed method (PM) showed a small positive bias, giving results that were on average about 6% higher than corresponding values measured using the WM. In this study, DO measurements were carried out in sample volumes ranging from 2 mL to 10 mL using the PM. Statistical analysis of these results indicate that the bias reported in the PM could be eliminated (i.e., limited to a ± 2% range) using sample volumes of 7 mL or higher. Use of a larger sample volume also enables lowering the least count of the PM to 0.1 mg/L O2 as compared to 0.25 mg/L O2 reported previously.