Which analyte requires filtration immediately and cooling, with 48 hours storage in glass rinsed with nitric acid?

Which analyte requires filtration immediately and cooling, with 48 hours storage in glass rinsed with nitric acid?

• A. Nitrite
• B. Phosphate
• C. Sulfate
• D. DO

Answer: (B)

Phosphate samples need careful preservation because phosphate can readily stick to glass surfaces and change form if left untreated. This is why the procedure calls for filtering right away to remove particulates, cooling the sample to slow any biological or chemical changes, and storing it in glass that has been rinsed with nitric acid. The acid wash reduces sites on the glass that would bind phosphate, helping keep the true phosphate concentration in solution for up to about 48 hours before analysis. This combination of immediate filtration, cooling, and acid-washed glass is specifically aimed at preventing loss or alteration of phosphate, which is why it’s the best choice for this analyte. Dissolved oxygen, by contrast, must be measured promptly because it rapidly changes with time and exposure; sulfate and nitrite don’t require this exact preservation approach.

Phosphate samples need careful preservation because phosphate can readily stick to glass surfaces and change form if left untreated. This is why the procedure calls for filtering right away to remove particulates, cooling the sample to slow any biological or chemical changes, and storing it in glass that has been rinsed with nitric acid. The acid wash reduces sites on the glass that would bind phosphate, helping keep the true phosphate concentration in solution for up to about 48 hours before analysis. This combination of immediate filtration, cooling, and acid-washed glass is specifically aimed at preventing loss or alteration of phosphate, which is why it’s the best choice for this analyte. Dissolved oxygen, by contrast, must be measured promptly because it rapidly changes with time and exposure; sulfate and nitrite don’t require this exact preservation approach.