Modification of Winkler's method for determination of dissolved oxygen concentration in small sample volumes

Winkler's method is the most popular procedure for determination of dissolved oxygen (DO) concentration in water samples. However, this method requires a relatively large sample volume of 200 mL for accurate DO determination. Many alternative methods have been proposed for measuring DO concentrations in small sample volumes, but most such methods have problems of either, low accuracy, high cost, complicated instrumentation or lengthy analysis times. In this paper, a simple modification to the Winkler's method is proposed for measurement of DO concentrations in samples of 1 mL volume. The proposed method is accurate, low cost, simple and quick. DO concentrations were measured in 33 samples by both the conventional Winkler's method (WM) and the proposed method (PM). For 23 of the 33 samples analyzed, the hypothesis that the population means of the measurements are equal (mu(1) = mu(2)) could not be rejected at 95 percent confidence level and for 19 samples, the hypothesis that the population variances of the measurements are equal (sigma(2)(1) = sigma(2)(2))could not be rejected at 95 percent confidence interval. It was thus concluded that in most cases, DO measurements by WM and PM give comparable results both in terms of accuracy and precision.