At what temperature should the sample for oil and grease analysis be kept?

The correct choice, which indicates that the sample for oil and grease analysis should be kept at 4 degrees C, is based on the requirement to preserve the integrity of the sample and minimize any changes in the composition of the substances being analyzed. Lower temperatures help reduce the volatility of oils and greases, preventing evaporation, which can lead to inaccurate results.

Maintaining the sample at 4 degrees C strikes a balance between preserving the sample and avoiding the formation of ice, which could impact the analysis adversely. This temperature is commonly recommended in laboratory protocols for environmental samples to ensure that the constituents remain stable until analysis can be performed.

Higher temperatures, such as room temperature or 10 degrees C, might increase the risk of changes in the chemical composition of the sample due to the potential for evaporation or other reactions that can alter the concentration and types of oils and greases present. Keeping the sample not exceeding 0 degrees C could complicate handling and analysis, as it might freeze certain components. Thus, 4 degrees C is the ideal temperature for maintaining the quality of oil and grease samples prior to testing.