What reaction is used to determine nitrite levels in urine?

The correct choice is the Greiss reaction, which is a chemical reaction specifically used for detecting nitrite levels in urine. This test relies on the principle that nitrites, which are formed from the reduction of nitrates by bacteria in the urine, react with specific reagents to produce a colored azo dye. Typically, the Greiss reaction involves the addition of sulfanilic acid and α-naphthylamine to the urine sample. If nitrites are present, a pink color will develop, indicating a positive result.

This method is particularly relevant in clinical settings for identifying urinary tract infections (UTIs), as certain bacteria that cause these infections can reduce nitrates to nitrites. Therefore, the presence of nitrites in urine can be a significant indicator of infection.

Other methods listed, such as Benedict’s test and the Folin-Ciocalteu method, are used for different purposes, with the former primarily detecting reducing sugars, and the latter measuring phenolic compounds. The Biuret test is used for measuring proteins through the interaction of copper ions with peptide bonds. None of these tests are appropriate for determining nitrite levels.