What is the best preservation method for twenty-four-hour urine samples for catecholamines?

The best preservation method for twenty-four-hour urine samples for catecholamines is the addition of 10 mL of 6N HCl. This acidification is crucial because catecholamines, which include hormones like epinephrine, norepinephrine, and dopamine, are sensitive to oxidation and degradation. By lowering the pH of the urine, HCl helps to stabilize these compounds and prevent their breakdown, thus ensuring that their levels can be accurately measured.

Maintaining a low pH in urine samples reduces the risk of enzymatic activity and oxidation that could occur if the sample is left unpreserved. Acidification not only preserves the integrity of the catecholamines but also minimizes bacterial growth, which could interfere with test results.

While cooling to 4°C has preservation benefits for some urine analytes, it does not offer the same level of protection against the degradation of catecholamines as acidification. Similarly, adding boric acid might stabilize certain substances but does not adequately preserve catecholamines. Mixing with ethanol is not a standard preservation technique for urine samples and could potentially interfere with the analysis of these hormones. Therefore, the practice of adding HCl ensures the best preservation of catecholamines in a twenty-four-hour urine collection.