Which analyte requires acidification to pH < 2 and has a 28-day maximum storage time?

Which analyte requires acidification to pH < 2 and has a 28-day maximum storage time?

• A. TKN
• B. Nitrite
• C. Phosphorus, Total
• D. DO

Answer: (C)

Total phosphorus samples are preserved by acidifying to a pH below 2 and then refrigerating, with a maximum storage time of 28 days before analysis. This preservation setup helps keep phosphorus in the dissolved phosphate form and minimizes biological activity or chemical changes that could alter the measured concentration. If you don’t acidify, phosphorus can precipitate or adsorb to container surfaces, leading to biased results. Other analytes have different preservation needs and holding times, so they don’t use this exact pH and 28-day rule.

Total phosphorus samples are preserved by acidifying to a pH below 2 and then refrigerating, with a maximum storage time of 28 days before analysis. This preservation setup helps keep phosphorus in the dissolved phosphate form and minimizes biological activity or chemical changes that could alter the measured concentration. If you don’t acidify, phosphorus can precipitate or adsorb to container surfaces, leading to biased results. Other analytes have different preservation needs and holding times, so they don’t use this exact pH and 28-day rule.