What substance can be used to preserve urine in microbiology?

Boric acid is an effective preservative for urine samples, particularly in microbiology. It serves to maintain the stability of certain components within the urine for extended periods, which is crucial for reliable microbiological analysis. By inhibiting the growth of bacteria and preserving the concentration of analytes, boric acid helps in obtaining accurate results when the sample is tested for pathogens and other microorganisms. The grey top tube is specifically designed for urine collection with boric acid, facilitating the stabilization of the specimen until it can be analyzed in the laboratory.

Other substances listed do not serve the same purpose. Sodium chloride is often used for various laboratory analyses but is not a standard preservative for urine. Potassium phosphate is primarily used as a buffering agent and does not preserve urine samples. Calcium oxalate is primarily used as an anticoagulant in blood samples, making it unsuitable as a preservation method for urine. Thus, boric acid stands out as the best choice for preserving urine samples in microbiological contexts.