Phosphates To 3 ml of urine, add 1 ml of conc. HNO 3 and 5 ml of ammonium
molybdate and warm gently. A yellow precipitate of phosphomolybdic acid
indicates the presence of phosphate.
Sulphates To 3 ml of urine, add 3–5 drops of 2% barium chloride (BaCl 2 ) solution
followed by 5 drops of conc. HCl. A white precipitate of BaSO 4 indicates inorganic
sulphate.
Ammonia Boil urine with equal volume of 10% NaOH. Smell of ammonia gas
indicates the presence of ammonium ion in the urine sample.
Calcium Add few drops of glacial acetic acid to about 5 ml of urine followed by
addition of 1 ml of 4% ammonium oxalate solution. Calcium is slowly precipitated
as oxalate as enveloped shaped crystals that can be observed under microscope.
7.5 Tests for Organic Constituents
Urea Since urea is the end product of protein metabolism, urea excretion in urine is
an index of protein intake in diet. Urea in urine is increased in exaggerated protein
metabolism, fevers, and increased adrenocortical activity. It is decreased in the last
stages of severe hepatic diseases and in acidosis.
7.6 Detection of Urea
Hypobromite Test To about 3 ml of urine, add two drops of freshly prepared
alkaline sodium hypobromite solution. A marked effervescence due to evolution of
nitrogen indicates urea.
Biuret Formation Test Evaporate 3 ml of urine to dryness in a test tube to evolve
ammonia. Cool and dilute the residue in 10% NaOH. Then add 1–2 drops of 1%
CuSO 4. A red rose color formation indicates formation of biuret from urea on
heating.
Creatinine Detection by Jaffe’s Picric Acid Test Add 3 drops of saturated picric
acid solution to about 3 ml of urine. Make it alkaline with few drops of NaOH
solution. The red color formation confirms formation of creatinine picrate.
Uric Acid Detection To about 3 ml urine sample saturated with Na 2 CO 3 , add
2 drops of Folin’s phosphotungstic acid reagent. Uric acid reduces phosphotungstate
in alkaline solution and forms blue color.
32 7 Examination of Urine for Normal Constituents