Detection
of Sugar in Urine Sugar is ordinarily not present in normal
urine. When the sugar level in blood rises above normal level, the kidney eliminates
the extra sugar through the urine. Sugar then starts to appear in urine. Generally Benedict’s
and Fehling’s tests are used to detect the presence of sugar in urine. These tests give
coloured precipitates such as: light green, green, yellow and brick red, depending on
the concentration of sugar present in urine. Benedict’s test Materials required: Urine sample in a test tube, Benedict’s reagent,
burner, test tube holder and a dropper. Procedure: Using a dropper, take a small quantity of
Benedict’s reagent. Now, add the reagent to the test tube containing
urine sample. Boil the sample over a burner for 2 minutes
holding the test tube firmly with a test tube holder.
Keep shaking the test tube as it is being heated.
A brick red precipitate appears, indicating the presence of sugar in the urine. Conclusion: On boiling the urine sample with the Benedict’s
reagent, the cupric ion present in the Benedict’s reagent is reduced by the reducing agent,
sugar, to form a brick red coloured precipitate of cuprous oxide. Therefore, sugar is present
in the urine sample. Fehling’s Test Materials required: Urine sample in a test tube, test tube holder,
Fehling’s solution A, Fehling’s solution B, dropper and a burner. Procedure: Using a dropper, take a small quantity of
Fehling’s solution A. Now, add the Fehling’s solution A to the test
tube containing urine sample. Using a dropper, take a small quantity of
Fehling’s solution B. Add Fehling’s solution B to the test tube
containing urine sample. Boil the sample over a burner for 2 minutes,
holding the test tube firmly with a test tube holder.
Keep shaking the test tube while heating. A brick red precipitate appears indicates
the presence of sugar in the urine. Conclusion: The cupric ion present in the Fehling’s solution
is reduced on boiling by the reducing substance, sugar, to form the brick red coloured precipitate
of cuprous oxide. Therefore, sugar is present in the urine sample. Precautions Handle the chemicals with care.
Thoroughly clean the dropper with distilled water before reuse.