What is the preservation requirement for Oil and Grease samples?

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Multiple Choice

What is the preservation requirement for Oil and Grease samples?

Explanation:
Oil and Grease samples must be preserved by acidification and refrigeration to keep the sample stable until analysis. Specifically, you add sulfuric acid to bring the pH below 2, then chill the sample to 0–6 °C and hold it for 28 days. The acid inhibits microbial activity and chemical changes that could alter the amount of oil and grease, while cooling slows any ongoing reactions and loss of analyte, ensuring the result reflects the original sample. Other approaches miss key parts: simply analyzing as soon as possible ignores the required hold time; waiting 48 hours or 7 days without acidification or cooling allows changes that can skew results; cooling alone without acidification doesn't adequately stabilize the sample.

Oil and Grease samples must be preserved by acidification and refrigeration to keep the sample stable until analysis. Specifically, you add sulfuric acid to bring the pH below 2, then chill the sample to 0–6 °C and hold it for 28 days. The acid inhibits microbial activity and chemical changes that could alter the amount of oil and grease, while cooling slows any ongoing reactions and loss of analyte, ensuring the result reflects the original sample.

Other approaches miss key parts: simply analyzing as soon as possible ignores the required hold time; waiting 48 hours or 7 days without acidification or cooling allows changes that can skew results; cooling alone without acidification doesn't adequately stabilize the sample.

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