If preserved with sulfuric acid, how long can a dissolved oxygen sample wait for analysis using the modified Winkler method?

When a dissolved oxygen sample is preserved with sulfuric acid for analysis using the modified Winkler method, the maximum wait time before analysis is crucial to ensure accurate results. The preservation step with sulfuric acid is designed to prevent the degradation of the sample by inhibiting biological activity and stabilizing the dissolved oxygen content.

In this context, the correct answer of 8 hours aligns with standard analytical practices for maintaining sample integrity. If the analysis is delayed beyond this timeframe, there is a risk that changes in the sample may occur due to environmental factors or chemical reactions, which can lead to inaccurate measurements of dissolved oxygen levels.

This preservation protocol allows for sufficient time to transport the sample to the laboratory or prepare for analysis while still providing a reliable assessment of the dissolved oxygen concentration within the set period.