Handling of the sample is critical to this procedure. The sample must be incubated within 48 hours of its original sampling time. Analysis after this point will have significant effects on the oxygen concentration within the sample and may often lead to less than accurate results. Usually, the DO of the sample will tend to decrease.
When the sample is first brought in for analysis, it must be maintained at a temperature of approximatley 4 degrees Celsius. This is to ensure the fact that the oxygen concentration will remain constant and will also inhibit the further growth of organisms. Once in the lab, the pH of the sample must be adjusted for analysis. The desired pH for this procedure is between 6.5 and 7.5 where bacterial growth is possible. A 100 ml sample is usually adjusted with 0.1 N sulfuric acid or 0.1 N sodium hydroxide depending on the original pH of the sample. Once obtained, the sample content is checked to deterimine chlorine content. Chlorine must be removed from the sample because it introduces an interference with the dissolved oxygen.
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