Nitrite tests

The nitrite test can be used to detect the presence of nitrate-reducing bacteria in the urine (such as E. coli). The leukocyte esterase test is a rapid dipstick test to detect pyuria. 

Reduction to nitrite test Nitrates are reduced to nitrites by metallic zinc in acetic acid solution the nitrite can be readily detected by means of the sulphanilic acid-a-naphthylamine reagent (see under Nitrites, Section IV.7, reaction 11). Nitrites, of course, interfere and are best removed with sulphamic acid (see reaction 3 above). 

Oxidising agents—diphenylamine test. Filter a portion of the sample md add 2 (hops of the filtrate to 1 ml of a 1% solution of diphenylamine in sulphuric acid. A deep blue colour, appearing immediately, indicates tiie presence of an oxidising agent. The test will detect hypochlorite (from domestic bleach), bromates, chlorates, iodates, nitrates, and nitrites. Tests to distinguish between certain anions will be foimd imder Metals and Anions (p.64). 

The presence of leukocyte esterase is indicative of pyuria. The detection of nitrite is indicative of the presence of bacteria that degrade nitrate excreted in the urine. The combination of the two tests is valuable in patients with urinary tract infection. The absence of both constituents is a valuable test to rule out urinary tract infection, thereby reducing the number of samples sent to the laboratory for further tests. The nitrite test may be less helpful in young children in whom the urine remains in the bladder for less time, thereby limiting the time for nitrite production. 

Cyclamate salts Nonalcoholic beverages Sodium nitrite test... 

The nitrite test of the Merck Co. detects as little as 10 pg H nitrite. It uses filter paper impregnated with an aqueous solution containing methanol, 1-2 g of a diazotizable amine, 0.1-0.5 g of a coupling component, and 2-8 g of solid organic acid per 100 ml. The paper is dried and cut into strips and is specific for nitrite independent of urinary pH. The test reveals significant bacteriuria when the bacterial count reaches 1 x lO ml of urine. 

Since all metal salts of sulfamic acid are water-soluble, this reaction is discernible through the precipitation of barium sulfate if barium ions are introduced. A qualitative test and a gravimetric method for nitrous acid (nitrite) are based on this precipitation. The converse of the nitrite test permits the detection of sulfamic acid by a spot test, provided sulfates and sulfides are absent. 

Nitrite, Test with Griess reagent, see page 364. 

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